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[Articles Home]  [Add Article]  

Helically Wound Linear Loaded Magnetic Loop Antenna

from Rich Fusinski, K8NDS on August 14, 2011
View comments about this article!

Helically Wound Linear Loaded Magnetic Loop Antenna

Object of the design:

There are many designs and information available on the net concerning “Magnetic Loop Antennas.”

Even though these antennas are a fraction of the size of a full size resonant antenna, size of the lower frequency loop can still be quite large for a limited size piece of property. The object of my design is to compact the size of a magnetic loop while trying to maintain the efficiency of the loop.

Theory of Design:

Anyone that has delved into the theory of magnetic loops knows that for smaller size loops result in very poor efficiency for lower frequencies. A magnetic loop for the 80 meter band should be 15 ft diameter to produce efficiency of 88%. Using a 3” diameter copper pipe at a 15 ft diameter will only produce a 7Khz band width. This band width requires very precise tuning.

By implementing my helically wound design I have designed a 6ft diameter loop that has the characteristics of a 80 meter loop that seems to emulate a 10 to15 ft diameter loop of a single conductor. The 80 meter bandwidth of my 6 ft loop is 11Khz. The loop construction technique provides for light weight and cost as compared to a 15 ft loop constructed from copper tubing. I have implemented this design by using just enough copper to take advantage of “Skin Effect”. This allowed me to use only a thin copper with more surface area then a heavy copper pipe while providing a good surface area of RF skin depth. At the same time I have raised the radiation resistance considerably while only raising the IR losses slightly. The ratio of Radiation Resistance to IR losses equals the efficiency.

With the use of PVC tubing and flat soft copper strap I have helically wound the copper strap around the octagon PVC substrate. The result is a two part gain; I now have the same length of copper conductor as I would have on a 10 ft single conductor loop while I have also raised the inductance by using the loading technique. There are still a few factors that I have not calculated yet. The use of loading and the distributed capacitance somewhat adds a mysterious factor to this design. I am still working out all the details. The apparent efficiency and the large increase in Band Width tell the story. So far my “seat of the pants measurements” has shown a great increase in the tightness of the doughnut pattern shape. The approximate 4 degree very sharp null I am seeing to near E field noise seems much tighter then my previous single conductor loops. I have also noticed from many signal reports that I am experiencing as much as 3 to 4 S-units increase/decrease in signal strength by rotating the antenna with distant stations. This seems to be more apparent depending on the angle of radiation being utilized at the time of contact. There may possibly be more horizontal radiation off the side then a normal single conductor loop; this is just theory for explanation at this point. The reason that I am theorizing the polarization is due to the fact that I have seen stations get much stronger broadside while I have seen others get much stronger in the plane of the loop. Text book magnetic loop theory states stronger in the plane of the loop. This is definitely the case for ground wave stations; I have tested this in depth with great repeatability. I can get a 3 to 4 S unit change at 20 miles on the 20 meter band, the signal will just about completely null broadside to the loop.

Details of building this design:

The Hi-Res photos that I am attaching to this article will tell more then I can describe, so I will not go into great detail.

Starting with the PVC octagon frame, calculate your PVC parts by the size of the loop you are going to build for the particular frequency range desired. View my photos carefully to observe how I mounted the SO-239 connector; you will want to do this before gluing any frame parts.

I used a hard temper piece of copper flashing for the underlay of the SO-239 connector. Soldering this connector as the photo shows is important. You will also see in the photo how the center feed from the SO-239 was routed thru the PVC- T. You will want to finish this part carefully before any gluing. I used a short length of ¼ inch copper tubing to follow thru the PVC T for stability of the connection. If this connection breaks after you glue the frame you will be in trouble! Fill the short length of tubing with solder then heat it a push it over the center conductor of the SO-239 and heat generously. The other exiting end out of the PVC T will then be supported by the T itself, this makes for a very strong connection point.

Use cleaner and good glue and glue the frame together, use your ingenuity when assembling the frame as to what parts to glue first. Once you glue a part and it isn’t right you may be in trouble.

Make sure to use both good quality PVC cleaner and Cement for good bond and stability of the frame. The frame will need about 3 coats of high quality Krylon spray paint. I use flat black as it hides well, Krylon makes a spray paint for plastics; this is the one that I recommend. If you do not paint the frame the PVC will deteriorate fast especially in the western state where I am located.

Now it’s time to wrap the frame, this part is a bit tricky the first time you do it. The rule that I used to build both of my loops is adding 37.5 % of conductor length to the amount of conductor required for a single turn loop. I am going give credit here to “AA5TB” the work on a great loop calculator. I use it constantly, I have compared it to hand calculations and it is very exact, just search the net for his Excel program. Plug in all the factors for the loop that you want to build and follow my rule for length of conductor. Use the width of the copper strap X2 in place of the circumference (diameter X 3.14) the formula requires diameter. You will want to divide the conductor and mark the center of the length. Start the wrapping at the SO-239 and pay attention to the pitch of the material. Again some ingenuity on calculating the wrap spacing is necessary here. You want to make sure that the two ends of the material come out even at the tuner feed point. If care is not taken here you will have an unbalanced loop. Once you have wrapped the loop if it came out even, then temporarily tape the ends in place while you solder the center of the flashing very carefully to the so-239 supporting foil.

Capacitor & Drive Motor Assy:

The tuning capacitor is one of the most critical devices in this build project. If you choose to use anything but a good quality vacuum variable capacitor you can expect many issues. First issue is power handling, my loops handle SSB full legal limit (1500wts), and I rarely run them at more than 1Kw. To keep the Q high and power capability high use a vacuum cap or you will probably be disappointed in the results. Humidity will also play a role in affecting your antenna by using an air capacitor. I am using a 12 volt gear reduction motor with a forward and reverse controller arrangement. The down side is the long times required to change bands. The reductions need to be slow for precise tuning, thus a single speed geared motor is not the best solution. My next loops will use a stepper motor system which I am currently looking into. With a stepper motor control and a PIC processor you can vary the speed to jump bands quickly, you can then use a system of fine tuning buttons to move about the band of operation.

Tuning unit mounted in the operating position.

Great care must be taken with all connections; every milli-ohm that gets multiplied in the main conductor will be subtracted from the total radiated power. This results in lower antenna efficiency. All overlapping joints in my loops were tinned on the underside, and then quickly heated with a torch. After cooling they were all solder with a very hot iron all around the edges. Try not to leave any sharp edges, there can be 15 KV at the area around the capacitor connection; some corona arching could happen at sharp points.

The Gamma Match:

I have tried several different matching techniques, most of them worked although I have not observed any difference by using the simple gamma match. The gamma match also seems to be the flattest match across the entire tuning range. Once tuned to the center of the tuning range of the loop design the match appears to hold a flat match of < 1.2 to 1 @ 50 ohms across the range. It will be the farthest off at the lowest band. It takes a bit of experimentation to get it perfect. Both of my loops are 1:1 @ 50 ohms except on the lowest designed band; there it may be 1.2 or 1.3 which is negligible.

If you tune your loop in the horizontal position, do not solder it in place until you mount it in the yard complete vertical. I just use a SS hose clamp to get the match, when you are satisfied then solder it to the foil and clamp over it to keep it secure. My 80/40 meter match was twice as long until I mounted it in the vertical operating position.

Match was 1:1 @ 50 ohms here, DO NOT SOLDER YET!

Rear view of gamma match in operating position, indicating how the SO-239 connection exits from the rear of the PVC T

Front view of gamma match soldered in place; 1:1 @ 50 ohms

More photos of construction in progress

Gamma Match – 20 thru 10 meter loop

20 thru 10 meter loop under construction, this one will be painted after finished

Loop Controller, controls both loops with side switch

Finished 20 thru 10 meter loop ….. Just needs paint

Radiating the Cows! Hi Hi……….

The author/ Designer Rich, K8NDS

Thank You for reading the article.

I hope that you have as much fun with these stealth antennas as I have had. It is a way for the HOA restricted Amateur operator to come very close to the performance of full size antennas.

Please look me up if you want to see these antennas in action, I think you will be quite surprised at the functionality of these small antennas. Many on the bands have heard these already and have stated how good the signals were………… in amazement!

You can find me whenever I am active on the bands by visiting QRZ.com and look up K8NDS -- Then just click on “MY QSX” link -- It will take you to my page where you can see what frequency that I am talking/listening on. Many have already done this. You can also view your own signal strength there while you are transmitting.

Member Comments:
This article has expired. No more comments may be added.
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 14, 2011 Mail this to a friend!
The important parameter for radiation is always the in-line physical distance in space we move in-phase current over. Always. We want to move as much net current over the largest PHYSICAL volume of space.

This means if we have a three foot circle, it is a three foot circle no matter how we pack wire in that circle. If we have a 20 foot long dipole, it is a 20 foot long dipole no matter how much wire length we pack into that occupied in-line area of space.

Going around in small circles inside a larger circle adds nothing except inductance and resistance to the results. Regretfully, all helcially winding the small loop does is increase inductance and loss resistance. It is of no benefit at all for radiation.

The only things we can do with a small antenna to increase efficiency are to decrease the resistance of conductors by making them shorter and wider, and make the current more uniform over the distance we have.

Making the current move more in-step and more uniformly over the distance we have maximizes radiation resistance. Making conductors as good as possible, as wide as possible, and short as possible over the physical area occupied minimizes loss resistance.

Helical winding does nether.

73 Tom

 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by K9WJL on August 14, 2011 Mail this to a friend!
Rich, Good article. Cant remember the last one I read all the way through.
I agree with Tom on his statements, but if its something small that works (even a little bit) and it fits the space and any other limitations a ham might have why not? It looks like fun to build regardless.
Have fun and good presentation. Ill be following this to see what else the gurus have to say.
73
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N2RRA on August 14, 2011 Mail this to a friend!
Great technical article Rich!

One thing I love about these articles. The person who doesn't go just by theory or books smart knowledge aquire's something far more valuable. Rewards!

All though Tom makes very valid points it can detour someone from experiencing the thrill of the experiment and results. You have to build to your specifications and reap the benefits. If there aren't many options for you due to space restrictions the magnetic loop will do fine. Wonderful thing is there are many options out there.

Thanks to Rich he gives motivation in his master piece and a means to prove it works.

I've spoken to quite a few builders of these loops over the years and one comes to mind which can't remember his call at the moment. This gentlmens loop on 80 meters with just 100 watts worked so well I thought he used a resonant 80 meter loop.

One thing you'll have to deal with is it's narrow band width unless you use a motorized tuning unit as shown above. Other than that have fun working stations and long QSO's.

Thanks Rich! You've motivated me to build one and see for myself.

73!

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KY6R on August 14, 2011 Mail this to a friend!
One very small antenna that I had the pleasure of using on the 20 - 10M bands was the Force-12 Sigma-5 GT. The antenna was only 9' tall, so would fit in any HOA restricted back yard.

The L.B Cebik web site had the full technical explanation of how it worked.

I'll never forget the day I worked 3C0V - where there was an unruly pileup and solar flares rendering my small yagi useless. I switched over to the Sigma-5 and worked this entity through the thundering herd.

Yes - I know - this is anecdotal, but the theory of operation seemed to back up why it worked so well on W4RNL's site.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K9MHZ on August 14, 2011 Mail this to a friend!
>>>>by N2RRA on August 14, 2011
One thing you'll have to deal with is it's narrow band width<<<<


This should be a red flag.


Don't get me wrong, I admire his motivation and willingness to share. But the laws of physics just don't let us squeeze an HF antenna down very much, no matter how hard we try. "Masterpiece" is a stretch.

 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by N0DET on August 14, 2011 Mail this to a friend!
Nice work Rich. I have built two Mag-Loops, as I have been condo-bound for years. Mine are 5 feet in diameter, and I typically work 40 meter cw, at qrp levels. I am amazed at the performance of these loops; much like everyone else! I placed the loop out on my 2nd floor wooden balcony, away from the gutter. The loop is quieter than the attic dipole, and definitey quieter than any random wire, or the gutter.
I did the poor-man method and used an appropriate length of coax for the capacitor (I had some RG-213 around). I stripped the free end of the coax and tune the loop by adjusting the braid - either scrunching back the braid or lengthening the braid over the center conductor, and then tape the braid in place. Certainly not convenient for jumping around the band, but I just chose my favorive 12 or 15 khz of bandwidth and called it good. BTW, this is only until I devise a tuning method, or somebody hands me a vacuum variable cap!) ;)
The narrow bandwidth is certainly not a red flag; this is indicative of the high Q of the antenna, where Q = quality factor, which for me in the condo meant greater noise immunity. The loop is certainly a quiet antenna (noise-wise)!

 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by ZL1PB on August 14, 2011 Mail this to a friend!
I was listening to him in ZL, he was a good 5-9 signal, I was impressed.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 14, 2011 Mail this to a friend!

Tom, I was expecting exactly the kind of response from some of you hams that cannot think out of the box. It is a real shame that people will boo-whoo something before they research the subject completely. If you were to use this antennas which you haven’t you would be more then surprised of the performance of this antenna. In the first place you obviously didn't get the idea behind this article or you didn't really read it which is a bad habit of many radio amateurs. The intention was to give an antenna a small footprint that could be used by restricted radio amateurs. It may not perform as good as a full size antenna but it comes very close. A solution for HOA hams! I don't see why some people have to just look for the bad in an idea, why not open you mind and look for the good side. I sure hope that you don’t actually think that all there is to know concerning antennas has been discovered? If that were the case we would all be stagnated in technology. I have some more stuff coming soon that will really surprise you.
If you watch my YouTube video, available on my QRZ page you will see that I worked VK4TUX twice now in the last few weeks on 40 meters with no effort. Email him and ask him about the comparison of antennas and how good my signal was, he is very popular and was very impressed both times now. If you were there you wouldn't be able to state what you did, I broke the pile ups on 40 meters but I guess that isn't good enough for you. I can't wait to run across you in a plie up were I beat you out with this tiny antenna! Now thatr will be fun, I do it all the time.
There are always better antennas out there especially for the appliance operators with big pockets that have the need to be king of the hill; that is not what this antenna is all about. I have NO use for buying something that someone else designed when it comes to antennas, being innovative is what the hobby should be all about.

If you would have read the article and went to my QRZ page to link to my web site you would have learned something. You actually stated in your response the exact reasons that this design works. The flat copper strap substantially increases the RF surface area while decreasing the loop diameter by helical winding, 3 inches equals about 6 inch surface area. The RF only utilizes the 1st few thousands of the skin area. The copper was selected to be just thick enough to provide for very low IR losses. If you do the math you will see that this is true. Just like you stated is raised the efficiency for the conductor. It really doesn’t matter how small an antenna is, it is all about efficiency, which you also stated. The efficiency of this antenna is very high, check out 7195 khz some time to see the reports that I receive; I think you will take all your comments back. I compare this antenna consistently against a 2.8 full wavelength doublet while on the air. 90% of the time it is 6 to 10 db better yet I have constantly worked the world with the same doublet. I think this antenna design is more than sufficient for HOA restricted Hams to be able to enjoy what most of us with space do now.
By the way hold several antenna patents that some actually are used in the industry.


 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by NF6M on August 14, 2011 Mail this to a friend!
I wondered about using copper flashing for one of these, but as you mention, the additional distributed capacitance and inductance make it hard to predict how it would work. It seems like a wide flat conductor like flashing should have more contributing surface area (hence lower resistance) than a pipe (I'm thinking that skin effect would cause the inner surface of the pipe not to contribute). Higher bandwidth is probably a bad sign indicating there is a bit more loss somewhere in the equation though. Thanks for sharing your results!
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by W6CAW on August 14, 2011 Mail this to a friend!
Just stumbled across Rich on 40M. Wondered by his strong signal if he was running his tiny little loop? He was. Compared to his long wire they were within 3 to 6Db from his house to East San Diego County. I was impressed!
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by G0GQK on August 14, 2011 Mail this to a friend!
Looks good and well made. Its for those with antenna restrictions ? What do you tell a busybody when they see that in somebody's back yard with all that shiny copper. "Yeah its a new type of clothes horse I've invented for the wife to 'ang her knick knacks on.

G0GQK
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 14, 2011 Mail this to a friend!
I'm sorry you took my purely technical comments personally. It is just an antenna. They work they way they work, they aren't God, women, or children so there is no need to be personally offended by comments about antennas, nor is there any reason to attack others personally in a technical response.

"by K8NDS on August 14, 2011 Mail this to a friend!
Tom, I was expecting exactly the kind of response from some of you hams that cannot think out of the box."

I'm sorry you feel that way, but let's try to keep this non-judgmental about each other on a personal level.


" It is a real shame that people will boo-whoo something before they research the subject completely. If you were to use this antennas which you haven’t you would be more then surprised of the performance of this antenna."

I doubt it. Very few antennas are surprising. I spent months measuring field strength of many loops. Even a change from a round tube to a flat strip of the same surface width reduces field strength. That's because current moves to the edges of the strip, instead of the more even distribution on a round conductor.

This is why, unless there are compelling reasons mechanically, high efficiency compact loops use round conductors.

"In the first place you obviously didn't get the idea behind this article or you didn't really read it which is a bad habit of many radio amateurs."

I'm sorry you feel that way, but I read it thoroughly.

"The intention was to give an antenna a small footprint that could be used by restricted radio amateurs. It may not perform as good as a full size antenna but it comes very close. A solution for HOA hams! I don't see why some people have to just look for the bad in an idea, why not open you mind and look for the good side."

No small loop antenna works as well as a full size antenna, and that was certainly not any point I made.

However, a three foot loop is always just a three foot loop. Factually, the more unnecessary conductor length we pack into the fixed area the narrower bandwidth can go and the higher losses will go.

That's right, narrow bandwidth is NOT a reliable indicator of low loss!! By increasing series inductance we can decrease bandwidth while, at the same time, increasing loss.

To know field strength, we have to measure field strength or heat.


" I sure hope that you don’t actually think that all there is to know concerning antennas has been discovered? If that were the case we would all be stagnated in technology. I have some more stuff coming soon that will really surprise you.
If you watch my YouTube video, available on my QRZ page you will see that I worked VK4TUX twice now in the last few weeks on 40 meters with no effort."

I can work VK longpath on 40 meters in the evening with a 6 foot mobile antenna on my truck. I have worked VK's with six foot antennas on 160, I used to work VK3IM day after day on 160 while he was mobile.

Why would anyone be surprised about working VK, or anywhere else, with a small antenna?

"Email him and ask him about the comparison of antennas and how good my signal was, he is very popular and was very impressed both times now. If you were there you wouldn't be able to state what you did, I broke the pile ups on 40 meters but I guess that isn't good enough for you. I can't wait to run across you in a plie up were I beat you out with this tiny antenna! Now thatr will be fun, I do it all the time."

You obviously have a great deal of faith in your antenna, but a few real reliably made FS comparisons against known properly working references would mean a whole lot more than what you think you can do.

"
There are always better antennas out there especially for the appliance operators with big pockets that have the need to be king of the hill; that is not what this antenna is all about. I have NO use for buying something that someone else designed when it comes to antennas, being innovative is what the hobby should be all about. "

Denigration of others on a personal level is out of place in a technical discussion.

"If you would have read the article and went to my QRZ page to link to my web site you would have learned something. You actually stated in your response the exact reasons that this design works. The flat copper strap substantially increases the RF surface area while decreasing the loop diameter by helical winding, 3 inches equals about 6 inch surface area."

Sorry, but that is not how antennas work. They do not work by surface area.

Radiation comes from charge acceleration. In a simple antenna a fraction of a wave wide, it is how many charges move in unison over the widest spatial area that matter. That means current over linear spatial distance. Nothing else.

A 40 meter dipole made from #14 copper wire, for example, has negligible radiation changes from the same dipole made from five inch pipe.


" The RF only utilizes the 1st few thousands of the skin area. The copper was selected to be just thick enough to provide for very low IR losses. If you do the math you will see that this is true. Just like you stated is raised the efficiency for the conductor. It really doesn’t matter how small an antenna is, it is all about efficiency, which you also stated. The efficiency of this antenna is very high, check out 7195 khz some time to see the reports that I receive; I think you will take all your comments back. I compare this antenna consistently against a 2.8 full wavelength doublet while on the air. 90% of the time it is 6 to 10 db better yet I have constantly worked the world with the same doublet."

A 2.8 wave doublet is a terrible reference antenna.

In the first place, a 2.8 wave doublet is full of deep pattern nulls. In the second place, efficiency can be all over the place depending on what is around the doublet and how the system is constructed.

The facts are:

1.) Surface area has nothing to do with radiation resistance. It is the ampere-feet that matter, and the "feet" have to be an in-line distance in space. If we bunch a 20 foot long antenna up in a three foot length of space, it is a three foot antenna. It isn't a 20 foot antenna, or even a four foot antenna.

2.) Bandwidth is determined by the ratio of L and C to resistance. If we increase reactance faster than resistance bandwidth decreases, even if at the same time we have increased loss.

Here's an example. Take a normal small loop and add a a small very high Q inductor in series with the capacitor. You'll find bandwidth gets narrower, even while efficiency drops. This is because we increased the reactance faster than R, but we still increases loss resistance. Radiation resistance on the other hand remains the same because the area of the loop did not change.

Please don't take my purely technical comments personally. I'm happy to see anyone experiment, but only when reliable test methods and references are used can we learn anything.

Have a nice day, and let's try to leave the PERSONAL criticisms for politics, religion, or at the local bar.

73 Tom





 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 14, 2011 Mail this to a friend!
The bandwidth is not too much higher if yo run the math vs a single conductor loop. I am not disagreeing with your statement, just going by performance.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 14, 2011 Mail this to a friend!
Hi there, good question. Actually the photo that you see is before I painted the whole thing flat black. It now blends fine in the foilage.... hi hi.
Many areas especially in Arizona have block walls around the yard as much as 7 ft high, no one would even see the antenna in that situation. If a person has many trees it can easily be hidden. The small 20/10 mtr loop is only 33 inches in diamter and one meter high. You could put some plastic foliage on that one for a discuise....hi hi.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 14, 2011 Mail this to a friend!
I just think that too many people just look at these articles to pick them apart, there is no need for that! I don't think that I am the one to be apologizing here. Yes it is just an antenna but it serves a specific purpose for a specific group. More hams should do work to preserve the hobby, more hams can enjoy the hobby instead of being stiffled by HOA's.
Even though I should not be apologizing, I am sorry but I see this so much here on Eham that it gets me irritated. I know everybody here wants to show off what they know, it is human nature. Let's try to respect what other write before jumping in with both feet!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 14, 2011 Mail this to a friend!
One last comment, probably the most important one. You can throw out all the techicalities that you want but the proof is in the pudding. These antennas work great. I have had all kinds of antennas for 48 years of ham radio, thus I do know what to expect from any antenna. I have allot of eperience in this area, I do know what I can expect to work with S-9 reports. Some times people put too much faith in the math, there are always many other factors that may not be apparent. Again the proof is in the pudding and my pudding is tasting real good!
So you can also not take this too personal because I am telling you like it is even though you may not believe it.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 14, 2011 Mail this to a friend!
Thanks much, there is about one dozen stations that have already started building these antennas. All of them are building because of the repetative QSO's that we have had where my signl was booming in time after time. Like I say the proof is in the pudding or they wouldn't be building them.
I hope that if you do build one you ahve as much fun with it as I have had; any help that you need please email me, I will be glad to give you any pointers to help you avoid any pitfalls. I already did some of those in my prototypes.

Rich K8NDS
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 14, 2011 Mail this to a friend!
Ya, It's a real shame when those "techicalities" and facts get in the way.........
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N9TGR on August 14, 2011 Mail this to a friend!
Rich.

First of all great article with accompanying photographs to give a good visual on the finished product.I used a 3ft magnetic loop for a couple of years and was always amazed on the job it did even when a couple of feet off the ground.Granted it would not measure up to my 4el steppir or 4 el quad at 75ft but it definitely always amazed me.I did not have the luxury of a variable vac but used 3/4-1/2 inch copper trombone on a 12volt reversible motor.
Sad to see we get fellow hams on the attack with their unfounded criticism instead of offering encouragement and praise on a well written article.
Keep up the good work and forget about the monday morning quarterbacks.

73s Andy N9TGR/EI8IM
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N2RRA on August 14, 2011 Mail this to a friend!
Quote Rich-"One last comment, probably the most important one. You can throw out all the techicalities that you want but the proof is in the pudding. These antennas work great. I have had all kinds of antennas for 48 years of ham radio, thus I do know what to expect from any antenna. I have allot of eperience in this area, I do know what I can expect to work with S-9 reports. Some times people put too much faith in the math, there are always many other factors that may not be apparent. Again the proof is in the pudding and my pudding is tasting real good! "

No need for sorry Rich!

There are people that are technically savvy because of book smarts. I can garentee that those same people who comment in a sought of negative way thinking they know everything with out even experimenting really know nothing. Proof is in the pudding!

It is a scientific fact that you can take a full size lets say 20m resonant antenna and squash it to something like a over a quarter of it's length or more but your bandwidth is compromised greatly. When I mean greatly I mean like only getting a few kilohertz of resonance. fractal antennas are a good example and their always improving on them with much success but with some considerable difference. I hope you get the drift though.

A properly made magnetic loop will work fine and with awesome results. So build with some positivity folks because that's what ham radio is about. If you looked at modeling programs all day or listened to someone who built them only on modeling programs your in for a boring ride. ;)

73!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by VK2FXXX on August 14, 2011 Mail this to a friend!
This article implies, to my understanding ,that the author believes , he has designed a 6 ft diameter loop ,that is as efficient as a 10-15 foot diameter loop.
ie a 6ft diameter loop that is 88% efficient.?
I cant seem to do that with any of my loop calculators using real material as the element.Must they all be faulty?

If you are going to put a section in your articles titled " theory of design" you better have that theory correct. There are people here that will point out fundamental mistakes in such articles,much to the dismay of people who cant accept constructive criticism.
Nobody said your antenna does not work,they just questioned the theory used ,its implementation ,and the methods used to determine performance.



Enjoy your antenna.
Brendan

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by VK2FXXX on August 14, 2011 Mail this to a friend!
The above applies to the antenna on 80m,as it will near 100% efficiency the higher in frequency it is used.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by VK2FXXX on August 14, 2011 Mail this to a friend!
I told a lie! a 6 ft diameter loop with a conductor 50 inches diameter!! will give 87% efficiency on 3.6mhz!!
using this calc ;]

http://www.66pacific.com/calculators/small_tx_loop_calc.aspx

Damn that technicality stuff.
Brendan
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by KB4QAA on August 14, 2011 Mail this to a friend!
Rich,
Thanks for one of the best articles in a long while. Your enthusiasm is obvious.

You should not bite back at Tom and others who merely point errors in electrical theory. Sharing projects is great, but ensuring that readers understand how it actually works is too.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N7BUI on August 14, 2011 Mail this to a friend!
Very nice article Rich. I tuned across you last night on 40 meters talking to a gentleman back east. Your signal on the loop was incredible. When you switched to the longwire(?) it was obvious the loop was the clear winner.

What value of vacuum variable capacitor are you using on the loops? I didn't see it mentioned in the article.
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by W7AIT on August 15, 2011 Mail this to a friend!
A cheap dipole will work better than all of this complex, hard to build copper foils, pvc pipes, etc. And the dipole works better. Keep it simple.
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by N2EIK on August 15, 2011 Mail this to a friend!
That plastic food container will last one year, maybe two. The UV will make them disintegrate. Been there, done that. Just and FYI, nice article.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W9PMZ on August 15, 2011 Mail this to a friend!
Really if these antennas are that efficient how can they be adapated to a mobile antenna? If the antenna is 88% efficient it sure would beat any screwdriver design out there... I have a Hi-Q 4-160 mounted on my vehicle which I expect it to be no more than 5% efficient... But I get great reports as well, but if I can get an increase of efficieny from 5% to 88% how do I do it? I could get rid of my 500W amp in the car and sell it at the expense of getting a better antenna...

73,

Carl - W9PMZ
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 15, 2011 Mail this to a friend!
Carl,

A vertical of a given length, when properly constructed with a reasonable groundplane, would have far more efficiency than a small loop antenna optimally constructed.

The disadvantage of a small loop antenna is in every point of space (every direction) radiation from one area of the loop opposes radiation from another area. There is no direction where radiation is in-phase. This cause radiation resistance to fall through the floor, which is why loop currents are so exceptionally high for a given radiated power.

The sole advantage of the loop is the open ends are brought close together, so a very high Q capacitor can be used to "load" the loop to resonance. This means with very careful construction to minimize series resistances we can have reasonable efficiency. This is in spite of the poor phase relationship causing such high currents. This loading arrangement, where open ends are brought together, also lends itself to easy band changes because a high Q high current capacitor is easy to build or buy.

However, if we want a single band and have a limited physical length of space available, a short dipole or vertical (with suitable groundplane) could have much better performance. It will not have the problematic out-of-phase fields the loop has, and will have much less current to radiate the same power. This means more efficiency, and no deep azimuthal nulls in pattern. There is also less stored energy, meaning wider bandwidth, if the loading system is properly done.

It's really tough to face the reality that every antenna is a compromise on some way, and there is no magic. It is pretty easy to convince ourselves there is magic.

For example, I have worked Europe on 160 meters SSB with some regularity while driving along to and from the Dayton Hamvention. That's not 40, that's 160. I've worked all over the world, including VK6, while mobile on 160. That's 10,000 miles on a lossy propagation band with an antenna the equivalent of maybe 2-3 feet tall on 40 meters. I've beaten stations in pileups from the truck with some regularity.

Now I could get all swell-headed about this, think I was a big powerful giant slayer or that I invented some new thing, but the fact is my antenna is less than 1% efficient on 160. The only reason it beats other antennas is either propagation, location, or how poor the other antenna is.

As good and warm and fuzzy as it feels to have head-filling ego pumping reports, I have to stay grounded in the reality that my signal would be 20 dB better from home.

I would actually do worse with a loop on the truck.

I know because despite what some people GUESS at, I have actually measured antenna field strength.

What is magic is the way a weak low power signal can be so good all around the world.....not any antenna.

Good luck on getting that 88% efficiency from a small loop. It can't be done with good construction techniques like a round welded smooth surfaced conductor, let alone by adding useless series inductance and resistance to the system through helically winding the element.

73 Tom
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 15, 2011 Mail this to a friend!
now now tom, bubba gave me a 59 with my super loop, so I'm afraid I have to disregard your technical measurements.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N2RRA on August 15, 2011 Mail this to a friend!
Quote: " I have also noticed from many signal reports that I am experiencing as much as 3 to 4 S-units increase/decrease in signal strength by rotating the antenna with distant stations. "

Forgot to mention one of the resourceful features of this project. "Directivity"!

I have read and been told by many loop builders that there is directivity in these loops. It would have to be a huge asset be able to null out signals or increase them. Of course as well as your signal going out.

Can't do that with a vertical unless it's a 4-square ,trapped rotatorable dipole ,or a full size wire dipole for that matter. Another good reason to experiment.

Since I've already picked up some materials for this project and thanks to W8JI's technical input but thanks to K8NDS project for motivation as well as technical input I'm gonna compare my loop to various mobile antennas and various others. I'm even gonna video them while showing comparisons in the field. When I do I'll post where to find it.

Another good thing about experimenting is for some that comment "throw up a dipole and keep it simple" ah dahhhh! Maybe they can't? That's the reason for the loop project and experimenting.

If any antenna no matter how inefficient it may be can get an op on the air especially in an H.O.A. environment why not build it or buy it for that matter?

If you built a 160 meter loop it would deffinitly be more efficient than a mobile antenna that can work the world and beat out other base stations. With propagation or not the point is it will work and propagation has a lot to do with it in any antenna. Maybe your QTH is in a propagation sweet spot. So if you build it despite minor claimed math guru on paper technicalities based on efficiency you might be surprised. Even more so if your one not able to put up a full size 160 meter dipole due to obvious reasons ,or for any other band for that matter.

Hey! If you can work the world on a mobile 160 meter antenna then a loop of this size can't be any worse. It can only be better. Way better. ;)

73!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by AI4WC on August 15, 2011 Mail this to a friend!
The author, Rich - K8NDS, is brave. He is also bold and literate and many other descriptors can be applied. I say the same for all the commentators. I learn from all, but I appreciate most the effort of Rich to build, document and share his particular experience with his magnetic loop. The statement that "All antennas are a compromise" is certainly true. Bear in mind also the wise saying: "In the end, it matters not what you say or what you believe; all that matters is what you do!"

Rich built a helically wound magnetic loop antenna that works.

Enough said.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K5AF on August 15, 2011 Mail this to a friend!
I could not agree more. Trying stuff is always productive. I've put up antennas that were supposed to work that didn't and vice-versa, but 100% of the time I learned something from the effort.

Interestingly, the helical loop was on my list of things to try. I was intrigued by an article from Vlad, UA9JKW, who had a 1-meter diameter loop that was wound with about 200' of wire and was closed at the top. He claimed it was the best 20M indoor antenna he has used. Here is the link: http://livestre.am/Pfu4 then go to page 1-10.

Since it is electrically long, it is not technically a mag loop, but i think there is great opportunity to try shrinking loop antennas with various widths of copper foil tape, and various tapers. Imagine a 3' diameter 80M loop!

I've been working with copper foil tape for several decades, my first design being a 20' helical vertical for 160M using 1/4" tape. That stuff ws relatively expensive back then. Now, I always watch eBay for deals, and I've accumulated over a thousand feet of copper tape of various widths to experiment with.

I taped a square mag loop onto a plexiglas panel and had great success with it, suggesting that you could do the same on a large glass window. In fact, the copper tape works great for end-loaded short dipoles. When you book your next hotel room, get one with a large, wide window! You can even work around a window frame and put a dipole up on two adjacent window panels, feeding it in a way that avoids touching the frame.

Anyway, this is great work from Rich. We all benefit from others that actually DO!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K1BXI on August 15, 2011 Mail this to a friend!
Rich, did you measure any common mode current on the outside of the coaxial feedline? If you did and found some, how much do you think it may have added to the overall radiated signal.

John
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3LCW on August 15, 2011 Mail this to a friend!
Rich,

I am impressed, quite interesting shrinking the loop helically. The fact you can load 1KW+ into it without heating shows it is potentially quite efficient. I would like to see how it would perform with an extended duty cycle mode with 500+ watts keydown. If the VSWR stays relatively stable that would be interesting.

I've increased small diameter 80M and 160M magnetic loop effectiveness by adding a second or even a third turn, but doing so seems to reduce the bandwidth even further.

Nice to see some fresh ideas.

Andy
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
I do not claim that I completely understand why this antenna works as good as it does. When I designed it my goal was to shrink the standard mag loop and still be able to tune 80 meters with a small foot print. I would say it works as well as anyone else’s 80 meter antenna in my local area. That is the only way to compare is with stations close by and on the air at the same time. I have done this many times now with quite the surprised comments from locals. To answer your comment that it would seem to be 100% efficient on the higher bands of operation; Yes It seems to be close to that on 40 meters. I can actually say that I have never had a 40 meter antenna work this well at any height that I have had one mounted. Then again I have never had one at 65 ft in height and out in a straight line. I have a larger Z in a small loop area do to the loading; I also have a copper surface area of the equivalent of a 2 inch copper pipe. If you use the Z of the loop and the surface area of a 2 inch copper pipe you will start to come closer the efficiency. If you work 40 meters we could set up a schedule sometime for you to compare signals from my area to mine just to get a feel for the performance. If you know VK4TUX, Adrian please contact him and ask him how I compared to others in the USA both times that we talked, he will tell you that I broke the pile ups both times. I heard many stations calling him right after me in which he only responded to one of them after several minutes of the stations calling while I received a 5/9 + from him.
Being in the down under I'm sure that you know that it takes a respectable signal on 40 to get a 5/9 + from here; a simple antenna usually doesn't do it well. So here I am with a 6 ft diameter loop 5 ft above ground that does it on a regular basis. I guess I will wrap this up by saying that it works; the reason that I was irritated with one of the previous stations remarks is it is like calling someone a liar when you are not there or you have not heard it on the air. I had a guy drive all the way from California last night to observe these antennas. I think that he may have been a bit skeptical because he has heard me on the air many times with a big signal using the loops. He left here in amazement after demonstrating both of my loops. He is in the process of changing his call right now; in a few days it will be W6DRG. Keep in mind this gentleman was a stranger to me until we had an eyeball other than one QSO prior. Look him up and ask an outside opinion.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
Hello Andy,

Now you are a guy with an open mind! We should talk sometime, I can see from what you wrote that you have a pretty good handle on what I am doing. I ran several prototypes before I built this design. I can answer your questions already because I have ran those experiments. Copper tape will not work, it is not thick enough and does heat with key down; the resonant frequency starts to drift after a few seconds of key down. This is also directly related to the diameter of the loop vs frequency. The closer that you get to 1/4 wave the less thickness that you need without heating. One of my loops is wound with 5 mil thickness; that is what I had on hand at the time. It will take 1kw for a few minutes then starts to heat just a bit; 8 mils (1.5 times thicker) will take 1 kw key down for a long time; thus can be run at 500 watts key down for extended periods.
It is all about creating a bit more Z in a smaller diameter while providing a large skin area and also using thich enough material to lower the IR losses. The inside of a thick copper tube is just wasted copper. Email me.........
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KC8VWM on August 15, 2011 Mail this to a friend!
"I would say it works as well as anyone else’s 80 meter antenna in my local area. That is the only way to compare is with stations close by and on the air at the same time."

---------------

Anyone is entitled to express that opinion and I really like the design. It's probably difficult to subjectively compare it that way, because a lot of antennas will often exhibit lobes and nulls in certain directions.

Other considerations involve near and far field effects in the Fresnel region and similar other factors such as take off angles etc. which may affect the perception of improved performance.

That is to say, unless there is a controlled test environment involved, the results or data simply cannot be stated with any reliable certainty.

It would be interesting to subject the design in controlled A/B tests with a reference antenna for further comparative analysis in the future.

I sincerely applaud your efforts and experimentation in this area and keep up the good work.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
Yep, been there done that before. The containers are so inexpensive that I bought 5 extras for that purpose. I also sprayed them since the photos, I sparyed my last one and it lasted for 2.5 years without deterioration. Try that next time!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
Hello Carl,

There is a big difference between a loaded 1/4 wave mobile and Mag Loop antennas. I don't think the wind load would work out to well with a large minor diameter loop flying around on the back of your vehicle. I do allot of mobile work and have home brewed many mobile antennas. I think we all know what it takes, large conductors, silver plating, large top hats ect. Your question was a good one! I am working on something cocerning my currentloop design in combination with a pateneted design that I cannot discolse here right now without a friends permision (which I am working on). I have built a prototype that is very interesting for mobile use and the results on the bench are very impressive so far.If I can get his permission I might have a solution for mobile, keep an eye out on my publications.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K5AF on August 15, 2011 Mail this to a friend!
I've been using 1.5 mil copper foil tape for many years at 100W and below with no heating or detectable losses. I would not suggest anyone to use it at the KW level.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K5AF on August 15, 2011 Mail this to a friend!
Rich,

What is the diameter of the PVC you are using for you 80-40-20 version? I think it is 2" but not sure. Also, where do you get the 120 degree elbows for PVC that large?

Also, did you choose the particular pitch for any reason? What does that make the physical length of the tape turn out to be?

I hope you haven't answered these questions already, I scanned the article but didn't see this info.

BTW, great video, I recommend it to everyone!

Paul, K5AF
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KC8VWM on August 15, 2011 Mail this to a friend!
All you need to know pertaining to the theory and operation of magnetic loops is published at the link below courtesy of Mr. Glen Smith and Mr. Victor Richard of the Microwave Physics Branch, Ballistic Research Laboratories, U. S. Army Aberdeen Proving Grounds.

Enjoy.

http://members.verizon.net/~vze24qhw/smith_1971.pdf


 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
Hello Paul,
Thanks for your interest; I 'm sure that you will be more than happy with the results if you build this antenna. There are a few that will be finished very soon; I can't wait to hear them on the air. The more there are the more believers there will be.
I need to revise and put up more details, I think that some of your questions can be answered by visiting my QRZ page, then use the link to my web page which has a bit more info there.
Here are your answers:
The elbows are 45 deg: 8 elbows at 45 deg each equal 360 degrees. They are available at any hardware store, home depot and such. A good place is ACE for a fair price. You will find molding protrusions on the elbows, file them off easily with a coarse file before gluing the substrate frame. 2 inch is correct, which gives you an outside diameter of almost 2.25 inches. If you wind the foil while trying to keep it flat as possible on that outside dimension the pitch will take care of itself. Wind one side relatively loosely (not pressure formed which you will do in the final winding) just to see how you come out in the end. Start with 35 ft of this material, it will likely come out just a bit long at the ends but you don't want to be short. Mine is spliced but spiced is not preferred; I will be rewinding mine soon. Mark the center of the 35 ft piece and solder it to the feed point making sure that you are using the correct pitch; some ingenuity is required here. Now you have 17.5 feet on each side; make sure that you come out very close to the same length on each end near the capacitor when you are finished. Use the SS hose clamps to procure the foil at each end. Now you can measure the length required to connect to you Vacuum Variable and trip off the excess material. Be careful of dressing the copper near any capacitor mounting interference objects. The voltage is so high anywhere near the capacitor that you will get arcing and corona if nor careful. I had only a 2 inch piece of foil exiting the capacitor mounting, it was about 1.25 inches from the mounting bracket; it arced and almost caught the breadboard on fire. It did melt the board where the board was fastened. All I had to do was reconfigure my foil to give on more inch clearance and it stabilized all. I hope this info helps in your build process.
One last comment; don't use anything less then 8 mil thickness for your foil. Contact me if you need a source. ………… Rich K8NDS
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 15, 2011 Mail this to a friend!
To know efficiency, we absolutely must measure field strength in comparison to a similar polarization known good reference antenna. The measurement method does not have to be calibrated for absolute FS, but the scaling needs to be accurate. In other words we don't care if 0 dB is 1 millivolt, we just care if 3 dB is really 3 dB change. Then, and only then, do we know relative performance.

I realize some people just like to know how things "feel". For people interested in **really** quantifying how an antenna works, here are some important points:

1.) With a compact antenna, we have to be very careful the feedline is not acting like part of the antenna. There have been many antennas, the EH antenna, the CFA antenna, and many others that unknowingly relied on feedline radiation to be a major part of the radiating system.

This is VERY easy to have happen in a compact antenna. For example bringing the feedline past the element, especially where very strong electric fields exist, can excite the feedline. So can the slightest non-symmetry in the feedpoint system. This is why small independent coupling loops and bottom feeds with the high voltage ends up in the air are the preferred loop arrangement.

A cold feedline can be verified by measuring common mode with a clamp on meter for some distance along the feedline away from the antenna.

2.) Heat is generally meaningless because conductors have air exposure and often a great deal of surface area. Unlike electromagnetic radiation, HEAT radiation is very surface area critical.

Heat can be used, with great accuracy, if the antenna is enclosed in a very well insulated box and temperature rise over long enough time is practical.

Feeling an antenna or watching for smoke is almost useless. As little as 30 watts can melt down a lumped inductor, while as much as 300 watts or more dissipation can be missed in a spread out wide surface area antenna. Even 5 watts of heat in the wrong spot can cause damage in some cases, while 1500 watts over a large surface area might not even be noticeable! Anyone who has soldered a variety of different area objects should have a feel for thermal conductivity and surface area. No one spits on a three inch wide foil to cool it from the heat of a 50 watt solder pencil, and all that heat is one spot! Spread the heat out, and many hundreds of watts are unnoticeable.

3.) Bandwidth is generally useless. So is feedpoint impedance. The exception is if we really know the system well, and understand what is actually changing the bandwidth or impedance.

Measuring something reliably and with pretty high accuracy does not take a great deal of equipment or time. Why anyone would invest time or effort and not go that extra step really falls back on two reasons:

1.) They don't know any better, and don't realize how easy an accurate meaningful answer is to obtain

2.) They don't actually want to know the real answer, because they are getting the (unreliable) answers they want or have already decided they are beyond being asked and responding to reasonable logical questions

Both or either of the above are eventually a waste of time for everyone. For examples just look into the CFA and EH antennas. There are at least a dozen antennas that don't work as claimed, but have investors and patents. Blind faith and refusal to consider constructive comments or valid points, or to use reliable test methods, is behind every long line of disappointed cool-aid drinkers.

Think about it...

The point of all this? When any of us think we have rewritten physics or science, the burden is on us to at least use reasonable verification techniques. That would include measurement of common mode current, and reasonable reliable comparisons. It is difficult to have meaningful data, so when it is totally missing it should be a major alarm.

Notice too I am talking about data, measurements, and how easy it is. Not about any antenna specifically except three examples (EH and CFA) that are now pretty widely known to be false theories.

73 Tom
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by HAMMYGUY on August 15, 2011 Mail this to a friend!
Nothing like writing an article for eHam to beat the enthusiasm out of the author.

Even good write ups turn into pissing contests.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N4JTE on August 15, 2011 Mail this to a friend!
Rich, A fine, nicely presented article. My only concern is that your estimation of how well your antenna works is based on your contacts here and there.
I would be more convinced if I knew you have worked a few hundred stations over a few months with various propagation before annointing this antenna as an answer for restricted sites. Comparing a loop to an horizontal wire with many lulls is not useful to those of us who do this stuff everyday. Nothing you have described would surprise a casual mobile operator with a Hamstick. However, you may have created a gem of an antenna that will outperform larger designs, but to be honest based on your writing, it's too soon to really tell. Will look for you on DX Summit.
Regards,
Bob
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N2RRA on August 15, 2011 Mail this to a friend!
"Nothing like writing an article for eHam to beat the enthusiasm out of the author.

Even good write ups turn into pissing contests."

LMAO! So true!

There's ways that one really smart guy that loves to criticize everything and not even give at least a pat on the guys back for trying. Always looking to steal the lime light from someone. LOL!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KC8VWM on August 15, 2011 Mail this to a friend!
There's absolutely nothing wrong with questioning or seeking additional information pertaining to it's theory of operation.

After all, we are all radio amateurs right?

???

Otherwise, if we dont don't engage in any techical discussion, I guess that means we are merely a silent audience watching another hokus pocus magic show demonstation with free kool aid.

Amateur radio is about experimenting, ivestigating and discussing technical matters with one another during the course of any proposed technical advancements.

Everything has it's technical challenges, merits, disadvantages, theory of operation, measured levels of performance and comparitive analysis.

As radio amateurs, it is supposed to be our job to discuss these ideas with one another including the idea of utilizing any collected data to make an informed analysis.

However, when all technical data is entirely absent and when all and any discussion or questions are no longer permitted and in fact entirely discouraged to occur in any way, then what is it do we have left exactly?

I guess I would have to conclude it is no longer what most people would consider a useful experiment involving amateur radio.

Nice idea, great pictures etc. but there's apparently nothing in the article left to discuss with one another is there?

As you can see, some of us have read the article and are merely just asking questions about things that seems to be lacking or not documented.

This is not somehow the fault of those who are reading the article.

We are merely demonstrating our interest and asking such questions. Isn't this normally supposed to occur in these situations?
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by K6SBA on August 15, 2011 Mail this to a friend!
Experimentation and building are the essence of ham radio. I have built and enjoyed several loops and consider them good candidates for extremely limited space situations.

That being said, W8JI has raised several points which have not been adequately answered. To wit:

1. How can the claims for this specific design be verified? Certainly the answer cannot be "they heard me better on this antenna than on antenna X or Y or Z."

2. Has the constructed antenna been tested, at a minimum, with a field strength meter against another reference antenna?

3. Most importantly, would this helically wound antenna on 2" PVC perform any better than a loop of the same size but made of 2" copper pipe? Now it could be that 2" copper weighs and cost a lot more than the material used in the author's antenna. His claim is that his antenna, for its size, will perform like a larger loop, but what is the evidence for this?

At a minimum, a side-by-side test of the author's design alongside a standard loop of the same diameter as the author's would at least yield some information. Without such a comparison, or better, some instrumented testing, we really know nothing.

The author's antenna does, in fact, have some real attributes compared to a standard loop; mainly light weight and low cost.

W8JI is, without exception, the most valuable technical contributor on this (and many other) websites. If you think his comments are just "academic and theoretical" putdowns, your conclusions fly in the face of his well-known experience and knowledge. If your subjective beliefs make you feel good, so be it. I'll stick with Tom any day.

73 de K6SBA
David in Santa Barbara, CA



 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by NB3O on August 15, 2011 Mail this to a friend!
Theory:
1. a coherent group of tested general propositions, commonly regarded as correct, that can be used as principles of explanation and prediction for a class of phenomena.

Field Strength:
1. the vector sum of all forces exerted by a field on a unit mass, unit charge, unit magnetic pole, etc., at a given point within the field.

Compare:
1. to examine (two or more objects, ideas, people, etc.) in order to note similarities and differences

Personal:
4. referring or directed to a particular person in a disparaging or offensive sense or manner, usually involving character, behavior, appearance, etc.

I don't not understand how a genuine interest of the first three terms relative to this article can be construed into the fourth.
But then, I sho ain't the sharpest tack in this box...
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
I really don't think you get the idea, I designed this antennas for a particular group a radio amateurs that need something like this; they can't errect text book antennas do to restrictions. I can actually say after all these remarks that I really don't care what anyone here thinks , I don't plan on waisting my energy doing all kinds of measurments for someone elses benift or because they don't either believe how good it works or for the most part just want to blow their own horn by trying to show everyone what they know. If someone wants to build one for the sake of argument and do all the measurments, go for it; that is why I am giving all the details out. That is a real bad habit of some of the people here on eham. So basically if you hear these on the air and you are so inclined to build one all the more power to you. By the way there are many already building these so you will hear others on the air soon. If not, I could really care less! I did not engineer these for profit or patent, I did it for the good of many in which allot of you don't understand because you have allot of space and no restrictions. It is not the best antenna in the world which requires a 100 ft tower and big deep pockets but it works better then most dipoles as where people in resticted HOA's can't even errect a dipole. So you can try to put the blame on me for firing back but I was not too happy with the comments that particualr things can't work when I know that they do; again I'm really not interseted in someone telling me that I need to make measurements. I have thousands of hours of measurements under my belt from my career, I am now in the hobby mode; I know how to do all that stuff I'm just not interested.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
Just to answer some of your questions. Yes , yes & yes.
I have already built several loops with copper pipe, with thick and wide copper strap and other materials.
Yes , I still had one made of heavy copper strap 1.5 inches wide and 3/32nd's thick errected to compare to the new design. Yes it worked about the same with reports of no significant difference with distant stations with an A/B test back and forth several times. The only difference was that my new loop is only 1/2 the diameter of the old solid loop and worked the same. They were mounted about 100 ft apart for the testing.

I worked for years with many guys like Tom, so you are not hurting my feelings by sticking with Tom. Whether you stick with Tom or not my antennas really work great for me and whoever else builds them, so what difference does it make?
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
Just to answer some of your questions. Yes , yes & yes.
I have already built several loops with copper pipe, with thick and wide copper strap and other materials.
Yes , I still had one made of heavy copper strap 1.5 inches wide and 3/32nd's thick errected to compare to the new design. Yes it worked about the same with reports of no significant difference with distant stations with an A/B test back and forth several times. The only difference was that my new loop is only 1/2 the diameter of the old solid loop and worked the same. They were mounted about 100 ft apart for the testing.

I worked for years with many guys like Tom, so you are not hurting my feelings by sticking with Tom. Whether you stick with Tom or not my antennas really work great for me and whoever else builds them, so what difference does it make?
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
Too much BS!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
Thank you, there is a nice way to ask questions and there is a rude way to just bascially state that someone doesn't know what they are doing, which Tom basically did. that's ok as I know many like him and know how to handle it. It's sort of like politics, you just ignore it!
You are exactly correct, there was some comment concerning Band Width from someone. These antennas exibit extremly small band width , that is part of why the effieciency is so good. I think some someone took some of my comments on bandwdth out of context. When I said the bandwidth increased, what I meant was that the bandwidth for a loop of that size icreased just as if it were the text book size. The person that said that of course knows it all!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 15, 2011 Mail this to a friend!
I applaud you! Yes I am bold; my New Years resolution was NO longer to ever keep what I am thinking to myself. I call a spade a spade and forever will do it. Politcal correctness has ruined this country. If I think someone is being rude to me which I did, I will let them have it with both barrels.
Keeping stuff to ourseves it what ruined this country. That is why we have the situation that we have now. Like I mentioned in another answer I have worked with people like that during my whole career. To make it short I almost always came out on the top.

Thank you again for your support.

Rich
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N4JTE on August 15, 2011 Mail this to a friend!
Rich it's called peer review.
Bob
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by N0AH on August 15, 2011 Mail this to a friend!
Rich-

Nothing against the technical reviews, but there could be a silent majority here that may have really enjoyed the article- FB and keep up the sharing- until you live on a lot of less than 100x100 feet, it is hard to appreciate this stuff- The guys at Isotron have been hearing it for decades (-:

73 Paul N0AH

 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by K6SBA on August 15, 2011 Mail this to a friend!
Hi Rich,

Perhaps the best thing about your article is that it has generated some very interesting comments and observations. I believe we used to call that a good conversation!

Someone previously mentioned the concept of "peer review." In my career I have submitted numerous articles to professional journals which were subjected to review and critique both before and after publication. Now I realize eHam is not a professional journal, but the concept of peer review -- without personal attacks -- is still valid.

I apologize to you if any of my comments offended you. My intent was neither to offend or belittle. Obviously you have demonstated a great attitude wanting to share your investigations with other hams so that they may benefit from your efforts. I sincerely applaud you for this. In this day and age of polarization of just about everything, acts of public generousity are truly appreciated.

That being said, let me restate my concerns. I currently own a homebrew 40" diameter loop made from 1" copper tubing. It does a pretty good job on 20- and 17-m. I interpret your article to indicate that your helically wound, linear loaded loop will offer better performance than my "standard" 40" copper tubing loop.

Now any loop requires some costs for materials and lots of labor. Add the cost of a quality vacuum variable cap, we now have an investment. My question is: before I embark on the expenditure of time and money to construct a loop based on your design, how can I determine whether it will perform better than the loop I already have? To me this can only be determined if there is some objective basis to compare "A" to "B".

I still like your loop because it uses light weight, low cost materials.

Again, I apologize if I unintentionally offend you.

73 de K6SBA
David in Santa Barbara
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WA7NCL on August 15, 2011 Mail this to a friend!
"I do not claim that I completely understand why this antenna works as good as it does."

I can't understand how you can "design" something that you don't understand.

I've always thought eham articles are long on words but short on numbers calculations and data.

But numbers are rude sorts of things anyway.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3LCW on August 15, 2011 Mail this to a friend!
Sometimes you can't wrap the math around the results. It makes for very interesting extended research.


Andy
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N2RRA on August 15, 2011 Mail this to a friend!
Quote: " My question is: before I embark on the expenditure of time and money to construct a loop based on your design, how can I determine whether it will perform better than the loop I already have? "

Build your own and find out. That will answer all the questions you have. Isn't that the point of experimenting?

Plus! Why can't most of you just build it and see if it works for yourself and compare it to what you have now on your property. All these technical variables do include location, location, location.

If some of you built several of them then you can afford another variable vac or just use one you have present. What's all the big deal people? Grow up already and stop competing who's penis or brain is bigger.

Gezz!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by ZENKI on August 16, 2011 Mail this to a friend!
I have heard Richs signal from that loop, his signal is a very good signal for such a small antenna.

I wonder if the ground conductivity or terrain profile is adding a boost to his signal. There is always a logical explanation why such a small antenna performs so well.

The claim and counter claims remind me a lot about the HB9ABX mobile antenna. This antenna is shrouded in mystery. At least there are no hidden secrets and payments up front required for the information in this article.

Anyone tried or built the HB9ABX antenna?

http://home.datacomm.ch/hb9abx/ant--abx-e.htm

I am not willing to pay for the construction article.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W5DXP on August 16, 2011 Mail this to a friend!
I don't know if anyone else has asked - but isn't this the same concept as the hula-hoop antenna from the 1970's? There was even an IEEE paper on the subject:

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1141158
--
73, Cecil, w5dxp.com
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 16, 2011 Mail this to a friend!
Cecil, I do think I've seen an antenna with wire or copper tape wound on a hula hoop.

But the IEEE paper you linked to is describing the antenna we would probably call a DDRR:

http://goo.gl/2ltv0

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
Answer to common mode current:
I am using an unbalanced match so it sould not be an issue. The antenna analyzer indicates a flat match at 50 ohms resistive plus of minus just an ohm or two.
If you noticed I have a coaxial choke on the large loop and a ferrite on the small one. This is always a habbit of mine no matter what antenna I build.
With a RF sniffer probe I have checked the coax and don't see much at all. Besides when the antenna is rotated there is a large difference in signal strength thus indicationg that most of the radiation is leaving from where it is intended to. My current shack is about as RF free as any other one that I have ever had. Always a good question.....Thanks for the curtious way of asking. Rich
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
W7AIT
If a cheap diploe is good for you, that is what you should be using! Simple antennas from the dark ages don't intrest me, they also aren't allowed in an HOA restricted environment. Again I will say that many are not getting the point of this article. Have fun with your cheap dipole!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
WB4JZY
Yes it is, just like politics everyone is correct in their thinking; they are always right!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
W8JI
Speaking of a big ego....Wow! Check out your mirror lately?
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
Not to worry Ham guy! Thanks anyway but I am used to this kind of stuff from people that think they know it all. My blood pressure is staying stable, I wonder about them? My friends that have all seen these antennas in action warned me about the remarks that I would get here, to me it is just comical.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W4AMP on August 16, 2011 Mail this to a friend!
I tend to agree with W8JI over the negative ones that have no understanding of electrical physics whatsoever. For someone with restrictive covenants this might be a workable antenna. But it will never come close to a simple half wave dipole. Not at 7 mhz anyway. I have always wondered why a ham would move to a property with home owners associations anyway. Several commercial antennas of this type have been marketed in the past by MFJ and others, but they all were for 14 mhz and up. I have noticed the strange trend of hams reviewing antennas by the stations they have worked. I do not know when this started, but stations logged really does not offer any evidence whatsoever to the efficiency and performance of an antenna. Antenna modeling and rf field metering can reveal the lobes of an antenna and give verifiable results.
I enjoyed the article, and encourage the poster to do more in the future. I also enjoyed W8JI's antenna theory references which I thought were given in a positive, constructive manner. Others that posted in this thread should have been banned years ago, and I believe they hurt eham in terms of financial support. Just one persons opinion that has been with eham since the beginning.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
Thanks Paul,

At least you understood the intent of this article. I have many stations building these antennas now just do to that fact of small space. I have allot of space; I am on a committee in Arizona to fight HOA restrictions on antennas. I despise HOA restrictions even though I am not impacted by them I wanted to help out the many that are impacted. I can guarantee you that this is one of the most efficient solutions to their issues. While designing these I realized after months of testing that in most cases I get better reports then on my large antennas; I use these all the time now and I switch every time I am in a contact; 90% of the time the loop is better. The loop is especially better on receive; signal to noise is considerably better every time. I know what some of the critics will say to that so I will head them off right here and now. Not only is the S/N better but the signal on the S-mater DOESN"T drop; in fact many times it is better. I have done subjective testing on antennas in my career for many years before taking measurements; I know how to do it so for those of you doubting Thomasas, you have NO idea of my experience.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K5AF on August 16, 2011 Mail this to a friend!
Have we forgotten who we are? I believe the term is AMATEUR Radio Operators.

That term affords us a certain freedom, we are not the IEEE or any other professional engineering group. In fact, I doubt that the majority of us holds any kind of engineering or technical degree.

Our amateur descriptor is not a liability, it is an asset. Our member include artists and engineers, musicians and mathemeticians. In almost any endeavor, both hard science and creative design complement each other.

To those who dismiss the performance of magnetic loops, I would argue that they don't appreciate their special properties. I've tried many small antennas in my 50 years as a ham, and I've yet to find anything that works better for its size than a mag loop.

Broad acceptance of this antenna category is understandibly limited because of narrow bandwidth, but performance capability is certainly documented. I recall several years back when the ARRL Sweepstakes low power category was won by a station with a single antenna, a mag loop. It is only a matter of time before someone will develop a matching network that will track a transceiver's frequency and maintain a low SWR instantaneouly.

Even performance is a relative thing. One man's "go-to" antenna is another man's dummy load. The amateur community is increasingly facing restrictions on antennas, and the capability that a mag loop can provide may be the difference between enjoying the hobby or giving it up.

"Seat of the pants" comparisons and personal observations don't pass the muster as scientific data. Today, however, we have tools like the Reverse Beacon Network, where we can get real-time results and use a comparison tool to evaluate different antennas. Even though there are slight time differences between readings between test antennas, I find the results to be remarkably consistent. But what I ALSO KNOW is that the readings merely confirm what I have already learned from the seat of my pants and personal observations.

When someone like Rich tries a novel approach that reduces the size/weight of an already small antenna, and appears to achieve comparable results, don't shoot the messenger or belittle his scientific method or lack thereof! Before taking him to the woodshed, replicate what he did, and prove or disprove his claims to your own standard of proof.

We wouldn't be where we are as Amateurs without folks Rich trying stuff and being bold enough to make a performance claim. We support Rich whether we prove or even disprove his concept, let's just have the decency to test or at least model his effort.










 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
Hello David,

I don't mind answering your questions as you have asked them very curtiously. Just for a bit more subjective information, there has been too much assumption here on this blog, you what they say about ASSUME?
If I were to write everything that I have done to verify the performance of these antennas I would have to write book, that was not my intention. I would rather keep working on my project as I have some valuable ideas to add to this project. I did not write this article to educate everyone on all the details. I was hoping that the antenna savvy people would pick up on what I have done. The not so technical in need of HOA antenna might just build one and be quite surprised by the results.
To get back on track here let me tell you that I have MANY times now been in LARGE groups on a frequency on both 80 & 40 meters. I am talking about stations in the numbers of one dozen. Ok now, they were in all directions around me, north, south east and west. Scattered around the western USA, almost as good as an antenna range (which I ran one for years). Yes this is not definitive data but more than good enough for Ham Radio HOBBY! (Not commercial) Antennas are sort of like vehicles to me. I like to drive a dependable vehicle that doesn't cost me an arm and a leg. You can buy a Chevy Cruise like I have and get 38 MPG like I am experiencing or you can buy a Large SUV or pickup gas hog. All I care about is that it functions and is dependable. Just like all my antennas, they all get me an answer almost every time that I call CQ, and most of the time 5/9, that is S-meter reading. I always ask? Is that with the preamp on or off, is that an honest report or is a stupid DX report 5/9 73 CUL.
Well back to the large circular group of my antenna range people; several times now I have done this with a large group. Every skeptic didn't know what to say as I received reports of a better or as good as anyone else in the entire antenna range. I have done this several times now, it is NOT a fluke. I am very capable of subjective testing and I may at sometime in the future actually take FS measurements. I am not interested in that at this time as I have already proven to myself the performance of these antennas.
I hope that this long drawn out explanation puts a bit more light on my claims. Of course the doubting Thomasas won't believe it. I say oh well!
If you want to build one of these I would be glad to discuss it on SKYPE or the land line, it takes much less time then writing on this blog, my email is avaiable. I would be glad to point you in the right direction and tell you a bit more of why I think this design works so well.

Rich
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
K5AF

Well Stated my friend!

By the way, you have read my mind.
I am currently working on stepper motor control that utilizes rs-232 output from the transceiver. This would be a great addition to the system. You could still fine tune with my button system once even close. This is a time consuming effort but I am making headway.

Rich
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 16, 2011 Mail this to a friend!
====================
W4AMP writes:

"For someone with restrictive covenants this might be a workable antenna. But it will never come close to a simple half wave dipole. Not at 7 mhz anyway."
====================

I don't think that's a reasonable critique. First of all, an unloaded 40m dipole is huge by comparison and isn't self supporting. 80m of course is worse. Second, if this antenna was built of smooth two inch copper pipe, it would be about 63% efficient on 40m according to EZNEC if I assume the joints add negligible resistance (possibly a bad assumption) and the capacitor ESR is around 20 milliohms (Q around 10,000). The comparison with a half-wavelength dipole is complicated when a loop in the vertical plane is used, because of the problems with ground reflection losses that have nothing to do with losses in the antenna.

I estimate that a conventional copper tube magloop of this size would probably be around a couple dB weaker than a quarter wave vertical in the loop's stronger direction. That's a more reasonable comparison if you insist on a "full size" comparison, because you can probably put a quarter wave or somewhat loaded 40m vertical anywhere you can install this loop, up to issues of stealth. A magloop would be stronger at high angles than a vertical which would be good for all-around communications including nearby stations.

The most important issue about this particular design, IMO, is to establish in some detail how the helical winding and single copper strip compares to a more conventional construction technique. In particular, I want to know what would happen if the loop was covered in copper tape running around the perimeter of the octagon and joined at the edges to form kind of an inexpensive copper tube. An apples-to-apples comparison of this against a more conventional magloop of similar cost would establish the advantages K8NDS claims, and that would help people make decisions better. Does "helically wound linear loading" really make that much of a difference? Is it really an advantage? Or is it actually a disadvantage or neutral?

The broader question of what the BEST antenna is for someone with limited space is also important in practice, and much more complicated. But the ANSWER to that question is never the same antenna for everyone. So it's not really a reasonable critique of an article like this to point out that this very electrically small antenna is going to be compromised compared to a full sized half wavelength dipole.

=========================
K8NDS writes:
" I am very capable of subjective testing and I may at sometime in the future actually take FS measurements. I am not interested in that at this time as I have already proven to myself the performance of these antennas. "
=========================

The thing I'm skeptical of is the claim that the helical winding improves the efficiency of this antenna in comparison to an ordinary magloop.

I'm fine with the idea that your tests establish that your loop is an antenna that performs well in a lot of ways. But you're making some strong, specific claims about the radiation resistance. I don't agree with the argument you're making about the radiation resistance from a theoretical perspective. And it seems to me that you don't give us direct evidence supporting your assertion that the helical winding is more efficient than not having the helical winding. I think you establish that your antenna is a good antenna, but that doesn't surprise me. Even if the helical winding ADDS loss as W8JI predicts, a six foot magloop built with copper strap and a vacuum capacitor with good attention to the connections will probably blow many peoples' 40m/80m magloop attempts out of the water!

I have a four foot magnetic loop constructed of 7/8" copper tubing with wide, heavy soldered strap connecting the tubing to a vacuum capacitor. (http://n3ox.net/files/magloopnew_lg.jpg) It is a pretty great antenna for a four foot loop used on 40m. I get good reports on it and people are legitimately surprised when I tell them what I'm running. I've worked a couple Field Days with it and it's great for that. Nevertheless, it's predicted to be maybe 25% efficient with respect to a lossless loop of the same size, and I have no reason to think a lot of aspects of my on-air success would be that much different with 25W radiated vs. 100W radiated, or even if my estimates are high and I'm only radiating 10W or so.

Given that you're completely satisfied by your results, I'm not going to try to convince you to make measurements on helical vs. not helical at the same size. But I'd guess the difference is small (and actually worse with the helical winding), and therefore you NEED careful FS measurements to show that. I think your claims of higher radiation resistance and more efficiency totally hinge on that measurement. I don't want to try to convince you to do anything at all. But I'd encourage ***potential builders*** to be skeptical that helical winding is better and directly test it at home.




 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by NU1O on August 16, 2011 Mail this to a friend!
"I have noticed the strange trend of hams reviewing antennas by the stations they have worked."

They do it in QST antenna reviews all the time and they should know better than to use anecdotal evidence.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W5DXP on August 16, 2011 Mail this to a friend!
> Cecil, I do think I've seen an antenna with wire or copper tape wound on a hula hoop. But the IEEE paper you linked to is describing the antenna we would probably call a DDRR: <

Thanks Dan, my memory is a little hazy on the subject of hula hoop antennas. I do remember the DDRR. I also remember a hula hoop antenna with a doorknob cap in the center but I can't find it on the web.
--
73, Cecil, w5dxp.com
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K1QAR on August 16, 2011 Mail this to a friend!
Rich

I've done a few loops ( http://x44.cc ) and would like to add a point that hasn't been made. They may actually have an advantage over a dipole due to the near field being primarily magnetic (H) which gives reduced ground losses.

I ran a 16 footer on 160 hung from a tree 15 feet off the ground. Using 3 inch aluminum, it was calculated to have 25% efficiency. It was in an average ham location with several houses, powerlines, and trees within 200 feet. However, a dipole at 30 feet also has 25% efficiency when considering losses from heating an "average" 5 milliSiemens/M ground.

Over the course of several hundred contacts over a year comparisons were made with others here in New England, with its mostly 2 milliSiemen ground. No surprise, it seemed to run with the "mid range" dipoles -- full size up 30 to 60 feet. It smoked the guys with 80 meter dipoles using a tuner, and guys with loe antennas. It was a couple S units weaker than the guys with dipoles or full wave loops up 90-120
feet.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K1BXI on August 16, 2011 Mail this to a friend!
This one from the QST archives is "something" like the authors......

Feb 1959 - QST (Pg. 46)
Hula-Hoop Helical Halo

One may have to be a member to view this. Just do a search for "hula hoop antenna" here:

http://www.arrl.org/arrl-periodicals-archive-search

Seems not much has changed in 60 plus years!

John
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by VE3EFC on August 16, 2011 Mail this to a friend!
When you shrink the size of an antenna something has to give. You give up efficiency or you give up bandwidth. The fact that this antenna gives up so much bandwidth probably means it has not given up much efficiency.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 16, 2011 Mail this to a friend!
===================
K1QAR writes:
"However, a dipole at 30 feet also has 25% efficiency when considering losses from heating an "average" 5 milliSiemens/M ground. "
===================

I just want to clarify for the sake of others following this discussion: you're talking about a **160m** dipole 30 feet above the ground, correct?
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
Wa7NCl
Isn't it nice to just take a bit out of someones writing completly out of context because you don't understand what you are talking about?
:)
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
Zenki
My ground conductivity here is very poor, all rock and sand. You are very correct that it may work differently for other surfaces.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
VE3EFC
Correct! BandWidth is not a concern with this type of antenna. In fact it is a large plus to have narrow bandwidth. When I tune anywhere else other then where I have resonance the antenna is dead, no detectable noise at all on the receiver; just as if you had the coax switch shorted out.
On 80 meters where the 2:1 bandwidth is only 11 khz I have excellent receive with great attenuation just a bit on either side of the operating frequency. Just like haveing a great filter out in your yard. I see so many hams striving for large BW when that always equals poor efficiency. When I am finished with this project my transciever will track the frequency of interest. Even as I have it, there is little issue in changeing frequency. I know that this seems difficult for some but simple for me and many others. I can change frequency within a band of operation from one end to the other in seconds or if changing in a portion of 40 meter phone 2 seconds or less.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
VE3EFC
Something else to consider: many of these mag loops are constructed from 3/4 inch hard line utilizing the circumference of the copper jacket. It is a good plan, cheap and sometimes available for the grabs.
If you calculate the circumference of the jacket it is: 2.355 inches of RF skin area. Using my design you have 3 inch open copper strap utilizing both sides (because it is not closed like a tube) you now have 6 inches of surface area. This is equivalent to a 2 inch diameter copper pipe but mine is very light weight. The slightly added Z do to helical winding tunes resonance with a smaller diameter then required with a single conductor, like a pipe or hardline.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K5AF on August 16, 2011 Mail this to a friend!
W8JI Comments:

The important parameter for radiation is always the in-line physical distance in space we move in-phase current over. Always. We want to move as much net current over the largest PHYSICAL volume of space.

This means if we have a three foot circle, it is a three foot circle no matter how we pack wire in that circle. If we have a 20 foot long dipole, it is a 20 foot long dipole no matter how much wire length we pack into that occupied in-line area of space.

Going around in small circles inside a larger circle adds nothing except inductance and resistance to the results. Regretfully, all helcially winding the small loop does is increase inductance and loss resistance. It is of no benefit at all for radiation.

My Question:

I've been reviewing all the information presented on this interesting topic but it boils down to this:

Tom, what you are saying is that no matter how we configure wire in a given space, there is no change to the radiation. So if I have a 20' dipole with densely packed coils at the feedpoint, or in the center of the conductor, or at the end points, or a distributed inductance (a helix) along the entire length, or even doubling the wire back and forth to create linear loading, the radiation will not change?

I'm not trying to challenge your expertise, but I find myself gasping for oxygen trying to comprehend what you are saying. Please help me understand!

Paul, K5AF

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
K1QAR
Well there is a guy that gets it!
Right on the money; exactly my thoughts and point to a tee!
As I have stated, not many have their diploes high enough to reap the efficiency that one would get on 160 to 40 meter using a dipole. Right on again; due to the relativly low ground effects compared to a dipole makes these loops shine in a direct on the air comparison.
Not many have the luxury of towers like a broadcast staion where they can achieve the height necessary for low angle radiation. I think we all know who I am referring to here!
Thank You! Rich
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 16, 2011 Mail this to a friend!
=====================
VE3EFC writes:

"When you shrink the size of an antenna something has to give. You give up efficiency or you give up bandwidth. The fact that this antenna gives up so much bandwidth probably means it has not given up much efficiency."
=====================

Unfortunately, that doesn't necessarily follow. It's possible to do things to antennas that reduce both the efficiency and the bandwidth at the same time, or that leave the efficiency exactly the same and reduce the bandwidth.

Simply adding inductance to a magloop is one example of this. Adding a lossless loading coil and reducing the capacitance to re-resonate results in a tuned circuit that has a higher Q and therefore a narrower bandwidth!

Here's an example of the VSWR of a series LCR circuit modeling a 160m magnetic loop with either 14 microhenries or 20 microhenries of loop inductance:

http://n3ox.net/files/magloopVSWR.png

The total resistance (Rrad+Rloss) in both cases is fixed to 50 milliohms, which makes the VSWR bandwidth unrealistically tiny (this is like a 16 foot aluminum octagon in free space run on 160m with no joint loss and no additional capacitor ESR, 2:1 VSWR bandwidth is around 400Hz, simple LCR model and EZNEC model more or less agree on that point), but the conclusions are valid for any situation where R is held fixed.

Because of this, it would be possible to add a low loss inductor in series with a magloop and simultaneously end up with less efficiency and narrower VSWR bandwidth. If the inductor loss is modest, the narrowing of the system bandwidth from the extra stored energy in the inductor and capacitor is enough to mask the extra loss from the inductor wire's resistance.

You should absolutely expect narrow bandwidth out of a small antenna, but you need to be careful thinking that narrower is better. Surprisingly WIDE VSWR bandwidth, much wider than you expect from your predictions and estimates, is an important warning sign that you've got extra loss that's crept in somewhere. This is a really important idea and helps you to catch problems.

But it's dangerous to conclude that NARROWER bandwidth IMPLIES efficiency, because it's not too hard to cook up situations where that's false. Another easy to understand example is just adding a high Q series resonant circuit to the feedpoint of a dipole. A concrete example from EZNEC: a 20m dipole 30 feet above "average" ground might have 1MHz between the 2:1 VSWR with respect to 75 ohms. If you add a 5 microhenry inductor and a 26 picofarad capacitor in a low loss resonant circuit in series with the feedpoint, the efficiency doesn't change in a way worth talking about (0.25dB if the coil Q is a measly 100) but the 2:1 VSWR bandwidth narrows to about 640kHz.

This isn't a very realistic example in practice, but it certainly could apply to antennas that use extra stubs, traps, or complex matching networks for other reasons... bandwidth and efficiency can easily both go down when there are extra tuned circuits in the antenna.
 
Magnetic Loop Antenna wins 1993 LP CWSweepstakes-  
by N0AH on August 16, 2011 Mail this to a friend!
My first antenna in 1995, bought the same day as my Cushcraft AP8A, was an AEA Isoloop 10-30M loop- it was fb but after time, I moved on- created too much QRM but worked fb-- first ever QSO from Colorado was with a KH6 station- then 5 minutes later, neighbor knocked- he had strung uninsulated wire throughout his house framing for rat shack stereo speakers- seems the circular pattern got into everything -

For our club station, KD0NIV, I got the MFJ 15-40 meter loop because I know the kids will really learn antenna theory from using it-

We'll see how it goes- If you have ever used a loop- they have a very high Q, that is, a narrow bandwidth- I believe this relates to efficiency-
-
In the May 1994 QST, (pg 21,22,23) Chip Margelli, K7JA, wrote of his "operating" experiences using the AEA 10-20M Isoloop antenna in Puerto Rico for the ARRL 1993 November CW Sweepstakes. He described to his enjoyment over-coming prior printed materials basically comparing the loops to low dipoles. He further went on to explain he was interested in results. This three page article is really amazing. HE WON THE 1993 LOW POWER CATAGORY ON A FT-1000, AN AEA 10-20 M MINILOOP ANTENNA, AND THE QTH OF NP4A.
-
"Stings Like A Bee" is how he put it comparing his win over the big guns- I really admire the fact that the point the author has tried to make over and over is when this antenna can be used and under what situation. There are three pages of how a magnetic loop antenna, with all of its flaws, can win SS. I don't keep every 16 year old QST in the shack, but I'm glad I had this one around!

73 Paul
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
K5AF
Hello again,
If you have a match on an antenna in which the analyzer says that you are 50 ohms resistive @1/1 swr only two major things are going to happen.
Either the power will be radiated or some will be lost as heat. There is very little IR loss in this antenna due to both large RF skin area and the thickness of the material. Thus high efficiency. Combined with very low ground effect equals the signal going somewhere. I wonder where it went?
there is very little heat loss as I stated earlier the current is so high do to the compacted area of the radiator with the conductor large enough for low losses. What I need is a thermal infrared camera to view this antenna at night. I don't have a good way to measure the voltage across the vacuumm variable although I know it is in the range of 15KV just because of the incident that I had with the mounting bracket being too close to the copper strap. It was about 1.5 inches away and still it managed to ark over until I moved it another 1/2 inch.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K6JPA on August 16, 2011 Mail this to a friend!
K5AF, I'm no antenna expert by any means, but I must admit that I've been asking myself the same questions, so I'm glad that you proposed the questions.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 16, 2011 Mail this to a friend!
=====================
K5AF writes:
"Tom, what you are saying is that no matter how we configure wire in a given space, there is no change to the radiation. So if I have a 20' dipole with densely packed coils at the feedpoint, or in the center of the conductor, or at the end points, or a distributed inductance (a helix) along the entire length, or even doubling the wire back and forth to create linear loading, the radiation will not change?
"
=====================

I know you're asking Tom and hopefully he will chime in, but the radiation resistance WILL change if you move coils around in general on a dipole, like if you go from center loading to end loading.

That's why top loading a vertical is much better than base loading it. On a 20 foot dipole even on 80m or another low band, you probably can't move coils around without changing the way the current distribution along the length of the 20 feet changes.

However, if you run an antenna like a really short dipole with big capacitance hats on the ends (http://n3ox.net/files/short_80_dipole.jpg) , the current in the radiating section will be nearly constant. At that point, it doesn't really matter wher e you put your loading inductors (if you even still need them) in terms of the radiation resistance. In a short hatted dipole, pretty much all that matters to the efficiency then is the loading inductor Q, because the radiation resistance just doesn't change much as you mess with the type of coils.

The same goes with a small magnetic loop, because it has nearly constant current around its circumference.

In GENERAL, changing the loading configuration changes both the radiation resistance and loss resistance, so it's important to look at the details, but you can be sure that constant current along the axis of the dipole is the best for maximizing the radiation resistance.

Putting compact loading coils and capacitance hats has been shown by a lot of people to outperform linear loading and helical loading in real life. That suggests something like this may be the best way to build a dipole:

http://n3ox.net/files/shortdip.jpg

It's impossible to PROVE that the above is the best way to load a dipole, but I would say there's rather good evidence that it's extremely hard to do better, and the only way to do better is to lower the loss resistance while keeping the favorable constant current along the dipole.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 16, 2011 Mail this to a friend!
============================
K8NDS writes:
"What I need is a thermal infrared camera to view this antenna at night."
============================

It would be a neat photograph, and would work okay on the one where you spray painted the copper flat black (wouldn't work worth a damn on the shiny copper one)

But it would be hard to turn the temperature of the keyed-down antenna into a dB power loss. You have to know how much heat is leaving the antenna due to the wind, and conduction to the substrate and you have to know that the cooling conditions are constant.

It would be a neat qualitative visualization of the heating on the antenna, but it would still not give a clear number for the efficiency.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 16, 2011 Mail this to a friend!
N3OX

Yep it would not be perfect although if you didn't see much heat while using a reference temperature in the same frame you could get a ballpark idea.
It would also show any places where improvemets in the conductor might be made.

Now this stuff is something that I could get into!
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by VE3EFC on August 16, 2011 Mail this to a friend!
N3OX has really got me thinking when he said "... it's dangerous to conclude that NARROWER bandwidth IMPLIES efficiency...". A dummy load has wide bandwidth and low efficiency. Now it would be possible to add capacitor and coil at the dummy load so it fakes razor sharp bandwidth. So I need to erase from my brain my rule that sharper always means more efficient. I learned something here.

Now let me ask about the opposite situation. I know a company is selling a screwdriver type vertical that claims once you have tuned the screwdriver for 20 MHz, the antenna will be flat (<2) all the way to 30 MHz. Am I correct in stating this antenna is behaving like a dummy load above 20 MHz and must be terribly inefficient?
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KC2KCF on August 16, 2011 Mail this to a friend!
K8NDS wrote:
"I call a spade a spade and forever will do it. Politcal correctness has ruined this country. If I think someone is being rude to me which I did, I will let them have it with both barrels.
Keeping stuff to ourseves it what ruined this country."

It would seem to me that being threatened with "both barrels" might be a strong incentive to "keep stuff to ourselves". Arguably, the "double barrel" approach could thus contribute to "ruining this country".

Just as well as the political correctness. I can imagine a parent complaining to teacher who corrected a child (no, 1+1 is NOT 5)... "But 1+1=5 is sooo creative and out-of-the-box thinking! If you keep insulting my child I'll get my double-barrel shotgun."

Thanks to Tom W8JI for sticking out his head and calling a spade a spade, despite a double barrel being pointed at him. It attests to his integrity as an engineer if he feels compelled to speak up against misinformation under such hostile conditions. (In turn, the word "always" in his explanation could be challenged, but the possible exceptions are somewhat esoteric.)

The irony is that the article would hardly lose anything if the one statement about "raising the radiation resistance considerably" was corrected. After all, antennas can work fairly well even without invoking supernatural powers.

Peer review is not an instrument to shoot down the author(s) (double-barrel or not), but to genuinely help improve and strengthen an article. It might be easier to swallow one's pride if the review process is not public. But if one is not comfortable with a public discussion, then why publish on a public discussion forum rather than a blog or a non-interactive medium like a traditional journal? (Nothing wrong with that, most respectable scientists and engineers go this way. They tend to be interested in correctness and insight and frequently don't fare well in discussions with opponents whose primary objective is "winning at all costs".)

The other thing to realize is that science and engineering are not democratic. Whether we like it or not, Mother Nature does not care about the popular vote what we would like to work, but unilaterally dictates what we can or cannot do. In a diverse discussion group such as here, the points of a few people who have a somewhat better understanding of Mother Nature than the rest may be worth paying more attention to than a majority of supporters who just happen to "like" a proposition.


 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 17, 2011 Mail this to a friend!
===========
VE3EFC:
"Now it would be possible to add capacitor and coil at the dummy load so it fakes razor sharp bandwidth.
===========

Exactly. Well... it doesn't FAKE it in the sense that the VSWR bandwidth is actually really narrow :D But yeah, a dummy load with a series resonant circuit has pretty bandwidth and radiates nothing.

To take it a step further, imagine building a PARALLEL resonant circuit inside a shielded box and looking for a 50 ohm tap on the coil. You can probably find one, just by transforming the loss resistance of the coil to 50 ohms. Or short circuit the output connector of a T-network tuner and twiddle knobs and see how many frequencies you can get a 50 ohm match on (do this with an antenna analyzer!) You can probably do it. There will be a narrow bandwidth 50 ohm match and absolutely no way for power to get out of the box :D

In those two cases, you're taking a fraction of an ohm of wire loss resistance and handily transforming it up to 50 ohms by using tuned circuits. So arguments like "there's nothing lossy in this antenna, just heavy copper conductors" can fall apart when even moderately complex LC networks are used!

===========
VE3EFC:
"Am I correct in stating this antenna is behaving like a dummy load above 20 MHz and must be terribly inefficient?"
============

There's an extremely good chance of that. You're absolutely right to start with a working assumption that the wide bandwidth is because the antenna is especially lossy. This is especially true if the antenna is very small and the match is good over **the entire range** from 20-30 MHz, instead of a SWR dip in each ham band in there.

A low-loss match over a broad swath of frequencies is harder to achieve than a bunch of low loss matches of narrow bandwidth. Think a 6BTV or something, which is a decent antenna with low SWR on many bands but is far from having low SWR from 3-30MHz. That's much easier to than making a no-tune match work from 20-30MHz.

Essentially every time a small ultra-broadband antenna like that has been on the market, it turns out someone stuck a resistor in a box or used a lossy ferrite transformer or used a coil winding technique with exceptionally low Q or something like that. However, I do think it's important to keep in mind that the existence of sham artists and resistor-in-a-box antennas does not mean that it's a scientific fact that every very broadband small antenna MUST have a resistor in the box.

In PRACTICE this is not very important (in practice it usually turns out that there's a resistor in the box) but there's an issue that people should keep in mind, at least in a philosophical sense. I doubt you can PROVE that you can't get less than 2:1 VSWR with high efficiency from 20-30MHz unless you know a lot about the details of the antenna. It would be difficult or impossible to establish that such a broadband match is absolutely impossible for EVERY POSSIBLE small antenna of a given size, even if you stay comfortably within the framework of well-tested physics.

There are some fundamental limits (Chu limit, Bode-Fano limit on matching) But they are fairly restricted in their application because it's difficult to say much about solutions to Maxwell's equations for a "general" antenna. In the end, as long as you're not violating a fundamental limit, what you really have to do is try many antennas looking for the one that gets closest to the limit. Some of the best bandwidth "small" antennas in the literature are particularly weird:

http://n3ox.net/files/goubaupic.png

(same Goubau as the single-wire transmission line: http://en.wikipedia.org/wiki/Goubau_line)

I don't really know much about the above antenna and won't unless I can get the proper paper (not the referenced one, which just reproduces that figure) in the library or inter-library loan, but it's cited widely in the small antenna literature and seems to be a gold standard for getting close to the Chu limit and has a very broad VSWR bandwidth for its size. You ever seen a ham using one of those?

There's never going to be a time when we've said "we tested all 20-30MHz antennas that fit in a five foot sphere and all matching networks of arbitrary complexity" That's literally impossible. So even when our intuition tells us to be deeply skeptical, it's good to keep a moderately open mind (REAL skeptics always do). Some really smart people with some computer optimization software to run through a hundred possibilities per second might cook up something that defies our usual useful intuition. Someone with DEEP intuition about correct EM theory and a careful protocol of painstakingly tweaking and taking field strength measurements might even cook up something really incredible in their garage.

If your interest is selling antennas, it's a lot easier and cheaper and probably makes about the same amount of money to just stick a resistor in a box, so many small, extremely wideband antennas end up owing a lot more to P.T. Barnum than they do Chu, Goubau, or any other solid scientists, mathematicians and engineers that appear in the history of and literature on antennas.

If you're just playing around with different small antenna configurations in your backyard without theoretical guidance and without making real field strength measurements, it's possible to trip into a bad situation where you've found a usable match and ***assume*** that you can't have much loss because you're using fat wire or other low-resistance conductor, like the parallel circuit or shorted tuner I mentioned before.

============

If you stick to antenna designs that are well understood, you can avoid most of the pitfalls of small antennas. Sometimes that's no fun, and it's good to get creative and experiment freely if you want. And if you want to present the results of your experimentation to others without a lot of hard data, that's fine too.

What I don't like is explaining how our unusual creation MUST work better than a more conventional antenna without showing hard field strength data or solid, detailed theory. For some reason, it seems that backyard experimenters mimic the actions of commercial antenna marketers and patent seekers; showing people a new weird thing and saying it works better seems more important than making sure it actually DOES work better and presenting strong evidence to that effect.

There's a lot of excellent guidance around about what's good and what's bad in straightforward and well-tested practice. I think W8JI's website among others lays "best practices" conventional loading techniques out very well.

I just wish there were more online examples of completely characterized designs that call out the antenna and coil dimensions and state clearly what the efficiency is on each band, preferably from direct measurements on the finished antenna. I'm working on one (similar to this: http://n3ox.net/files/shortdip.jpg) but I think I've got a really big stovetop and finishing this antenna is on the sixth burner back.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by ZENKI on August 17, 2011 Mail this to a friend!
There is a nice Automatic Magnetic Loop Antenna tuner project article in the August issue of Radcom. The article is by G3LDO.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K9MHZ on August 17, 2011 Mail this to a friend!
>>>>by KC2KCF on August 16, 2011
Peer review is not an instrument to shoot down the author(s) (double-barrel or not), but to genuinely help improve and strengthen an article. It might be easier to swallow one's pride if the review process is not public. But if one is not comfortable with a public discussion, then why publish on a public discussion forum rather than a blog or a non-interactive medium like a traditional journal? (Nothing wrong with that, most respectable scientists and engineers go this way.<<<<


Perfectly stated. And to note, not a single person was rude to this thread's author. His reaction to genuine debate and opposing opinion was that of feeling personally attacked. Seems strange for a debate over just an antenna.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K1QAR on August 17, 2011 Mail this to a friend!
In answer to the question, yes, a 160 meter dipole at 30 feet.

I did an infra red temperature scan of that 25% efficient 160 meter magloop antenna mentioned earlier.(the big hexagonal one on http://x44.cc ). Even with 500 Watts for several minutes, there was no measurable heat rise using an infra red thermometer with a 10:1 "cone of sensitivity", except one spot where a mounting bracket was. Turned out it needed tightening. Also tried unsuccessfully to deice it using what should have been about 375 Watts of I**2 R losses (75% of 500 Watts)

Incidentally, efficiency and bandwidth do appear to be related: the 2.5:1 SWR bandwidth (which happens to be the inverse of Q) went down from .105% to .085% (2kc to 1600 cycles at 1885 kc) after that bracket was tightened.

Surprisingly, it gave a decent sound on 160 AM, where my modified ricebox put out about a 6500 cycle bandwidth
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 17, 2011 Mail this to a friend!
=====================
K1QAR:
"Incidentally, efficiency and bandwidth do appear to be related: the 2.5:1 SWR bandwidth (which happens to be the inverse of Q) went down from .105% to .085% (2kc to 1600 cycles at 1885 kc) after that bracket was tightened. "
=====================

Sure, absolutely. If you hold inductance and capacitance fixed, or close to fixed, and you reduce the resistance, the Q will increase and the bandwidth will decrease. I'm certainly not saying that there's not a relationship between efficiency and bandwidth if you're careful about the details. If you add and subtract even small loss resistances from a magloop you should be able to see a clear relationship between bandwidth and added resistance.

But it's important to understand that you can change bandwidth without changing the efficiency at all even if you just add lossless reactance...

Q = 1/R * sqrt(L/C) for a series LCR circuit. If you keep the same resonant frequency 2*pi*f = 1/sqrt(LC) but add some extra lossless inductance and reduce the capacitance to re-resonate, the Q of the system will go up (sqrt(L/C) gets bigger, R does not change), but the total resistance (radiation+loss) will stay the same, so the efficiency stays the same.

In real life there's no such thing as adding a lossless inductance, so what will really happen is that bandwidth will go down and loss will go up slightly if you add more ***non-radiating*** extremely high Q inductance to a LCR circuit.

The reason why magloop efficiency and bandwidth both go when you build a physically bigger magloop is because the radiation resistance grows very fast with loop size (fourth power of the loop size in wavelengths). Loss resistance only grows linearly with loop circumference. The fast growth of the radiation resistance means that the Q goes down despite the increased L and reduced C of the bigger loop and the efficiency goes up because the radiation resistance grows faster than the loss.

But you have to actually make the loop physically bigger. Adding MORE stored magnetic field energy in the form of a compact inductor is bad, and there are special conditions on the loss in that added "lumped" inductor that lead to the counterintuitive result that loss goes up but bandwidth goes down.

Later today I'll try to write down and make some plots about the conditions where adding compact loading inductance to a small loop will make the VSWR bandwidth go narrower while reducing the efficiency.
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by N0CU on August 17, 2011 Mail this to a friend!
K8NDS: Rich, I have three questions:
1) from what has been stated in some of the posts, the gain of a loop is proportional to the area of the loop. Is this due to the decrease in efficiency (due to the constantly decreasing radiation resistance) as the size is reduced, as occurs with a vertical monopole?
2) Does the pattern change much with size?
3) Do you have any idea what the efficiency of your design is? A/B tests with skywave signals are interesting, but can be misleading since so many variables are involved.

Bill N0CU

P.S.: Thanks for taking the time to share your design with us, AND being willing to put up with all of the BS that can show up in the replies. The last artilcle I wrote for eHam resulted in me being ripped for working on my own equipment- that will probably be the last article I write.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W9ZSJ on August 17, 2011 Mail this to a friend!
I am enjoying this thread, alternately agreeing, then disagreeing, then becoming annoyed with how obtuse half of you are, then rejoicing in how insightful the rest of you are. I think I'd like to reread the whole thread again.

BUT, can I do that so that the rejoinder comes after the message which it counters? Do I have a preference set wrong? This is highly non-linear communication as I am seeing it on the screen at the eHam website.

Some may see a connection between "the other guy's position" here and the Dilbert strip for today, Wednesday, August 17.

George, W9ZSJ
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 17, 2011 Mail this to a friend!
Maybe it is OK to state again how all antennas radiate. This is a universal truth, looking at small antennas of any type.

Radiation occurs from charge acceleration over physical linear distance between two points in space. It always comes down to ampere feet over actual distance in space. Always. Unfortunately for small antennas, that rule is unbendable.

It is never surface area. Although there are antennas that claim this, none hold up under independent verification. The CFA and EH antennas are prime examples, and Isotron and others are included.

When spatial length (not conductor length) is decreased, current has to increase to make the same ampere-feet integrated over the same linear distance over space. This is why current increases as we shorten a vertical for the same total electromagnetic radiation. This applies to every antenna.

Packing extra conductor surface area or length in a given spatial area does not make decrease net current for the same electromagnetic energy. This is why helical mobile antennas never win mobile shootouts for the same length when compared to identical size lumped loading.

As for bandwidth, it is not an indicator of efficiency unless we understand the system and how the system works. Incredibly narrow antennas can have terrible efficiency, as can very wide bandwidth antennas. Very wide bandwidth antennas can be efficient, but they generally are large.

The important thing often forgotten is because a theory is wrong, and because a design is not optimum, it does not mean the antenna will not radiate and make contacts. It would be nice if we could talk like adults, and avoid the drama-queen responses. In the clear a poor efficiency loop antenna might be -10 dB from a well constructed full size 1/4 wave vertical monopole, while a great antenna might be -3dB below the monopole. The missing 7 dB is easily lost in propagation, or can be made up for with a slight increase in power.

This small difference is why, when we measure things, we need a good reliable reference antenna of similar pattern and polarization. With small antennas we have to be especially careful to ensure the feedline is not acting like the antenna, because it is pretty easy for a 50 feedline shield to out-radiate a two foot antenna. This is actually how the CFA and EH antennas worked, and why they mislead experimenters into thinking they invented a new form of electromagnetic wave creation.

Arguments about the EH and CFA were long and heated, and no amount of conversation could sway some people, but in the end we look back and after 20 years no commercial stations, besides those directly controlled by or involved with inventors, are using the antennas. No independent person with reliable experience has ever seen one that actually works.

By the way, I spent months measuring field strength of small loops. This is not all "theory". In my experience they work exactly like good engineering textbooks predict, as has every antenna I have ever measured (and I have measured hundreds). If they ever don't, it always turns out I overlooked something like feeder radiation.

Propagation and how well some pretty low powers will propagate are where 99% of the magic is, not antennas. That's why I can work Japan on 160 meters with a <1% efficient mobile antenna from Georgia.

73 Tom
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N0YXB on August 17, 2011 Mail this to a friend!
ZSJ and Dilbert (on 8/17) have summed it up pretty well. It's too bad some have had their feelings hurt and resorted to personal attacks because this is a very interesting thread.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 17, 2011 Mail this to a friend!
What is your name by the way?

Please let me know what screwdriver ant that is?
First of all < then 2:1 makes me wonder a bit.
I would have to say that I am very skeptical about that spec.
I doubt if the antenna is very efficient.

These guys that I call professional critics among other names really try to pick out points that don't really pertain to
my design just to pick it apart. I think it is just like on guy on the blog stated "it is a penis measuring contest"
I'm not into that so I am not answering any more questions on that blog that I feel fit that bill.
They can argue among themselves...Hi Hi..............

Yes a dummy load is a good example of a broadband antenna, purely resistive.
My antenna is exactly the opposite, very high Q: almost to the limit of Q that can be obtained unless you used good quality
silver plating.

Rich K8NDS
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by N0AH on August 17, 2011 Mail this to a friend!
More information on the AEA Isoloop, MFF loops, and magnetic loops in general:

http://frrl.wordpress.com/2009/03/21/limited-space-antennas-the-small-transmitting-loop-antenna/

several references, charts, etc.....52 links to magnetic loop websites-

Of note, The capcitor is covered as it can create a mess of any bird, dog, bat......etc that decides to sit on it during tx- hihi

 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by W1CTN on August 17, 2011 Mail this to a friend!
Rich,
A very well thought out and nice article to read. Too bad you are being flamed for your research.

I worked you recently and was impressed with your signal. As an active ham for over 40 years I think I know what a good signal sounds like.

As I had commented to you, I thought you were in W8 land and not Arizona, with the commanding signal you have. I have listened to you since that QSO and your signals are consistantly good here in Connecticut.

Your antenna is perfect for HOA's, nosey neighbors and PITA wives.

You have outlined the parameters of the loop very well in your article...

Thanks for sharing your antenna with the ham community.

73
Dave
W1CTN
Radio Ansonia
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 17, 2011 Mail this to a friend!
================
K8NDS says:
"These guys that I call professional critics among other names really try to pick out points that don't really pertain to
my design just to pick it apart."
================

Let me ask a very focused question about your design, one that is very pertinent:

Setting the cost of copper aside, why should I helically wind it with flashing instead of using a regular copper pipe loop?
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 17, 2011 Mail this to a friend!
N0CU

Hello again, one of the few people here that know how to have a debate with out a "penis measuring contest"!
You seem to be fairly intersted in this antenna. Why don't we talk, I can then tell you many details that are far too time consuming to try to write it all here. I think the rest of the doubting Thamasas can either build one to disprove my theory or wait until they see these poping up all over the air with big signals. Every day I work stations on 40 meters that keep repeating (without my asking) how strong my signal is considering band conditions. I guess acording to all the know it all critics here that doesn't really matter; what matters is the calculations that they are making while probably missing some impportant issues that hey are not intelligent enought to comprehend.I tried to share something here that I have had VERY good results with and I will state again that I probably know more concerning subjective testing then most on this blog. I did it for years in my career with great results. Then followed it up with antenna range measurements that almost always depicted what I already learned in th e field testing.The HOA hams that build these are going to be extremely satisfied and that was the whole point of the article. I have other normal antennas but I keep using these on the air because they are working so well. As one great actor used to say "Alice I don't give a Dam" Send me an Email direct and we will decide how to communicate at that point.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 17, 2011 Mail this to a friend!
K9MHZ

I didn't publish this article for a debate, I published it for a certain group of needy hams, you can deabte it yourself if you like. All that matters to me is that it works and it works well!
Is anyone reading? How many times do I have to say the same thing?
For those of you that think it doesn't work, again I really don'e care. Go away and read something else. For those hams that want an antenna for a resticted space situation you will love it!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 17, 2011 Mail this to a friend!
Thanks much Dave, I remember our QSO as it was poor conditions and a bad time of the day for AZ to Conn on 40.
Hope to run across you again soon and TNX much for the compilments! Rich
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 17, 2011 Mail this to a friend!
"Perfectly stated. And to note, not a single person was rude to this thread's author. His reaction to genuine debate and opposing opinion was that of feeling personally attacked. Seems strange for a debate over just an antenna."


spot on....there is only one person who has not acted like a gentleman in this discussion...and it is clear to see.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KU5Q on August 17, 2011 Mail this to a friend!
"RE: Helically Wound Linear Loaded Magnetic Loop Antenna Reply
by W8JI on August 17, 2011

Propagation and how well some pretty low powers will propagate are where 99% of the magic is, not antennas. That's why I can work Japan on 160 meters with a <1% efficient mobile antenna from Georgia.

73 Tom"

===============================================

Excellent wisdom
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 17, 2011 Mail this to a friend!
WB4JZY

Are you a CB'er ????
Your call sign is not listed, or are you just a red neck boot legger?
How big are the wheels on your pick up?

You wouldn't know the definition of rude if you fell on it!

What part of " I didn't put this up for a debate didn't you understand", I put this up for information of something that I already know works for what it was intended!

My QUOTE of the day for you:

Nothing in the World is more Dangerous then Sincere Ignorance!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K1QAR on August 17, 2011 Mail this to a friend!
Why helical winding? What I like about the design is you'd likely use less copper,and thus less $$ to build than one made the conventional way with pipe.. The efficiency depends on the surface area of copper, due to skin effect. Cost depends on the weight of copper, so the substantially greater thickness of pipe is a disadvantage.

It appears to my eye that the pitch of the helical winding is such that it may have minimal effect -- the genius in this design is using the inexpensive PVC instead of copper as the structural support.

An interesting application was a magnetic loop way up at 136 Kc, using thick wire hung between telephone poles. As I recall, it worked quite well.

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 17, 2011 Mail this to a friend!
K1QAR

You are very observent.
I actually measured the Z of a same size loop of a single conductor before I made the current design.
The Z of the 80/30 mtr heical winding is only about 10% larger then the Z of the single conductor loop of the same circumference. At the same time I have a wide suface area with little use of heavy copper.
The Z equates to about the Z of a 10 ft loop. (diameter)
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 17, 2011 Mail this to a friend!
"Are you a CB'er ????
Your call sign is not listed, or are you just a red neck boot legger?
How big are the wheels on your pick up?
You wouldn't know the definition of rude if you fell on it! "
What part of " I didn't put this up for a debate didn't you understand"

there you go, your true colors showing though. Name calling and innuendo, all symptoms of someone who can't put forth a coherent argument. Do yourself a favor and look up the word "debate". And if you want to participate in a public forum, grow up and act like a man.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 17, 2011 Mail this to a friend!
I am finished with this article, this is my last post.
Anyone interested in building one of these antennas are welcome to contact me via email like many are doing already. I will be glad to give you any pointers so you can enjoy the performance that I am doing with mine. Don't bother contacting if you are out to argue of whether this works or not. When I buy a product that I have read on reviews that works well, I usually am quite satisfied with it. I'm not selling this antenna, it is intended for a particular group of interested Radio Amateurs particularity designed for HOA hams. By the way that was the title of the article! There are allot of commercial antennas out there that I have seen people erect that cost allot and don't work worth a dam. This one is fairly reasonable and you will be very happy with it. I will leave all interested in debating this to debate with each other....Have fun!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N4JTE on August 17, 2011 Mail this to a friend!
Tough crowd here Rich, nicely documented and tnx for presenting a great article and most of the comments shared interesting thought provoking ideas that real antenna buiders appreciate.
Best regards,
Bob
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W5DXP on August 17, 2011 Mail this to a friend!
Seems the unanswered question is whether it works better than an all copper loop of the same size and, if so, exactly why? What term(s) in Maxwell's equations would account for that?
--
73, Cecil, w5dxp.com
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W4AMP on August 17, 2011 Mail this to a friend!
By K8NDS:
"WB4JZY

Are you a CB'er ????
Your call sign is not listed, or are you just a red neck boot legger?
How big are the wheels on your pick up?

You wouldn't know the definition of rude if you fell on it!

What part of " I didn't put this up for a debate didn't you understand", I put this up for information of something that I already know works for what it was intended!

My QUOTE of the day for you:

Nothing in the World is more Dangerous then Sincere Ignorance! "





Totally uncalled for.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K5AF on August 18, 2011 Mail this to a friend!
From W5DXP

>>>Seems the unanswered question is whether it works better than an all copper loop of the same size and, if so, exactly why? What term(s) in Maxwell's equations would account for that?>>>

Cecil, thanks for reintroducing some objectivity into the discussion.

I've reviewed the original article and realize, as have others, that there has been some very good work done here in terms of this being perhaps a practical alternative to a much larger, heavier and more expensive design. Rich deserves a lot of credit for that.

As I re-read the article now that all the rancor has died down, a couple of things jumped out at me.

First of all, the title seems incorrect. There is no linear loading involved in this design as far as I can tell.

Secondly, Rich discusses the 80M bandwidth and compares the newer, smaller helical design against a much larger 80M design, in other words a 6' diameter loop against a 15' diameter loop. He discusses bandwidth of the two loops on 80M, but then proceeds to confine his testing to 40M!

Please correct me if I'm wrong, but mag loops are generally defined as .1 wavelength or less in circumference, and most designs I've seen are in a range between .05 and .1 WL.

A 15 foot diameter loop would have a physical length circumference of approximately 47', so it would be approaching a .1 WL design, depending on what portion of 80M was used. On 40M, however, this design would be approaching a quarter wave, and would be physically large for that band, and not represent performance of a typical mag loop.

On the other hand, the 6' diameter design has a circumference of about 19 feet, which is about .075 WL on 40M (again depending on where on the band you are operating), which is a pretty typical size, well within the "norms" of Mag Loop design.

If this mag loop could be used efficiently on 80M, this design would truly be a "reduced size" loop. The increased bandwidth seems to suggest otherwise.

On 40M, it can hardly be considered reduced size, it is an expected size, and should perform as a typical mag loop. To determine if the helical winding is contributing anything to the performance, it should be compared to the same-sized (6') loop that uses the same copper strap material but is not helically wound (Again, thanks W5DXP).

In the area of subjective testing, I would cut Rich some slack. First of all, few of us have access to a perfect antenna test range or to a perfect reference antenna. This leaves us with on-the-air testing. Rich has an abundance of subjective and anecdotal evidence, and welcomes others to work him and observe his comparisons. He obviously has a powerful presence on the band with this antenna. Any field strength testing he might do over imperfect and inconsistent ground with other objects and structures in the way would be every bit as flawed as on-the-air tests. Perhaps we could leave it at that.

So, with the focus of testing centered on 40M, this design is hardly a breakthrough. Nonetheless, the construction detail, the reduced cost and weight, and a lot of on-the-air success with this design cannot be dismissed. Thank you, Rich, for preparing the article. Regretably, civility became the victim in what should have been enlightened discussion.



 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by RADIOPATEL on August 18, 2011 Mail this to a friend!
Dear OM K8NDS

Where do we get the capacitor? any RS catelogue no.?

Describe alternative arrangement if the same capacitor is not available.

Regards

VU2DCI
Dinesh Patel,
Mumbai India
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 18, 2011 Mail this to a friend!
The only contentions or claims I have read that seem strange are that winding a helical winding, which this antenna clearly is, packs more conductor surface area into a given volume of space and this somehow enhances radiation.

I've intentional avoided focusing on the actual design and stayed with those claims, because those ideas rewrite everything ever known about antennas.

First, antennas have been around since the 1800's. There has been nothing since the very beginning, well over 100 years ago, that has shown surface area or the length of a conductor packed in a volume of space has anything to do with radiation.

Hundreds of people far better equipped, far more knowledgeable, with far more time and funding to look at this than anyone present here today has never found anything that disagrees with the basics, that for short antennas it all comes down to the in-line ampere feet where in-phase charges are moving.

This is why dipoles are 1/2 wave long, and why specialists in electromagnetics, aside from the occasional hoax like an EH or CFA, knows we want maximum current over a linear distance through space.

When, after nearly 200 years, we make a counter claim, a reasonable burden of proof falls on the claimant to show what part of established theory was wrong, or at least that the device works as claimed.

K5AF said it is difficult or impossible to measure relative performance, but that notion is clearly very wrong. It actually takes less time to measure relative performance with reasonable accuracy then it does to collect random meaningless reports. Not only that, it can be VERY accurate. It should easily be possible to get within a fraction of a dB without a test range. I could measure, within a fraction of a dB, the relative performance of this loop to a 1/4 wave monopole with only an S meter, step attenuator pad, and a little clear room around the antennas. The very worse requirement would be physical space and the effort to install a good predictable reference antenna. Soil would not matter at all, so long as both antennas were over the same soil.

Some of us might be excluded because we live on city lots or have no clear space, but many are not excluded. The real lack is in will to really know, or lack of understanding in how to actually do a valid comparison.

The excuse that relatively accurate comparisons cannot be done does not wash, not by a long shot.

What we really have here is a claim that spiraling a conductor inside a given loop perimeter makes the loop work like it is physically larger. That claim is supported by honest well-intentioned claims similar to this:

"I am loud for such a small antenna"

"the antenna usually beats my 2.8 wave doublet"

"the impedance is the same as a larger antenna"

"the bandwidth is reasonable"

"I beat people in pileups"

None of those claims, no matter how well-intended, actually mean anything so far as verifying the idea that Maxwell and the rest (like Kraus, Jasik, and so on) over the past 150 years or so were wrong.

I've avoided talking about the actual antenna design, because ultimately it is the **theory** that is detrimental to our population, but let's look at designs in general.

Many times when a small antenna **ACTUALLY** works far better than it should act, the reason turns out to be feeder radiation. The EH antenna and the CFA antenna, as well as antennas like the Isotron, all make extraordinary claims. In all of these antennas, exceptional performance for size has been traced back not to a change in theory but to design errors. The feedline radiates, and thus the antenna is much larger than claimed.

We can go beyond theory and look at this particular design, but since just trying to start a healthy productive debate about measurement methods and how radiation works was taken personally, we probably better avoid specifics.

73 Tom





 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 18, 2011 Mail this to a friend!
====================
K5AF writes:
"Secondly, Rich discusses the 80M bandwidth and compares the newer, smaller helical design against a much larger 80M design, in other words a 6' diameter loop against a 15' diameter loop."
====================

That was the thing that I worried about. In the comments, it's said that the "Z" of the helical 80/30m 6 foot loop is 10% larger than that with a straight conductor, and that it's then the same as a 10 foot loop, but in the article it says the 6 foot loop is acting like a ten to fifteen foot loop.

I can't even make these comments consistent with each other unless I make some very strange assumptions about the measurement of "Z." Unless K8NDS decides to come back, we can't ask more detail about that, but if he just measured the loop impedance by connecting an analyzer where the capacitor went, the impedance is entirely dominated by the inductance of the loop.

A ten foot loop has roughly double the inductance of a six foot loop, not an inductance 10% higher. Both EZNEC and AA5TB's loop formulas agree with that. The impedance Z = R+jX should have R very very small because the radiation resistance and loss resistance are both so tiny you could barely measure them. Then The magnitude of Z |Z| = sqrt(R^2+X^2) is approximately |Z| = X, and Z = jX. X = 2*pi*f*L, so if the measurement was done at the same frequency, the size of Z should be proportional to the size of the inductance L.

So a ten foot loop should have a "Z" 200% larger than a six foot loop. The comments about how the loop "acts" like a ten to fifteen foot loop have, IMO, zero evidence to back them up unless I'm deeply misunderstanding the scant information that K8NDS presents here.

========================
K5AF writes:

"Any field strength testing he might do over imperfect and inconsistent ground with other objects and structures in the way would be every bit as flawed as on-the-air tests. Perhaps we could leave it at that.
"
========================

No way! Field strength testing is **nowhere near** as bad as subjective over-the-air tests in terms of the dB numbers that come out if you use some care.

The flaws that arise in controlled field strength testing are there, but they're much different than the flaws you will get over the air subjective testing.

Sometimes people act like a cluttered backyard is a magical place of special horrors that makes it IMPOSSIBLE to predict what an antenna is going to do and totally mess up ANY measurements you could EVER make. That CAN be the case. If you've got a bunch of grounded 30 foot metal poles in your backyard, trying to measure a 40m vertically polarized antenna there is going to make you tear your hair out and get bad answers. If you are so constrained that you always have to have your antenna within five feet of a house or something, it's probably going to lead to fundamentally flawed FS results.

=================
K5AF writes:
"To determine if the helical winding is contributing anything to the performance, it should be compared to the same-sized (6') loop that uses the same copper strap material but is not helically wound (Again, thanks W5DXP)."
=================

That's the central question that needs to be addressed with objective FS measurements, because the article makes a strong claim that will get many people excited. A 15 foot loop is not exactly a stealthy object. If a six foot loop can be made to work as well as a 15 foot loop, that would be great.

So the central issue is establishing that the difference in performance between a six foot octagon with helical copper tape vs. one with a straight copper tape conductor, and you can probably do that in a small cluttered backyard.

The key is to CHECK to see if SMALL changes in your measurement setup cause BIG changes in the results and to conduct several trials replacing one antenna with the other. That's how anyone would do it anyway for this particular question given that a second vacuum cap just for testing would be insane :D

Because the antennas are similar in size and design and operation, they will have pretty similar near field configurations. The interaction between both antennas and the earth and surrounding objects will be very similar. The only major huge errors would arise if the re is major coupling to a nearby resonant structure or if the field strength measurements change a lot when you move and rotate things a couple inches or a few degrees.

You don't know how badly these things will affect you until you start measuring, but you can MEASURE the ERRORS too! If you keep the field strength meter a fixed distance from the loop and move it in a circle while you rotate the loop, and then move the whole setup, loop plus meter around the yard in several different orientations, you can figure out if the loop is interacting strongly with anything.

If the FS reading doesn't change much when you re-orient and move around the whole test setup, all the stuff in your backyard is pretty transparent to RF at the frequency you're testing. Flip the position of antenna and meter and see how that changes things.

If you've more or less established that you can put the FS meter and antenna some distance apart and get answers close to each other, you can just set up the meter and loop and just swap the two different loops back and forth a bunch of times without changing anything else. That holds all other variables constant and you'll get results that are as good as your FS meter can be trusted to be. As long as it doesn't rain in the middle of your tests, you'll get quite accurate results.

A small backyard will mean you're doing near-field measurements, but that's okay to establish losses in the loop, etc.

=====================

In the end, this kind of testing is difficult and boring and time consuming. But it's never HOPELESS to try to get a good dB number on the difference between two similar antennas. Even if you DON'T do any checking of the backyard for sensitivity, you'll get an answer that is better established than "I get good signal reports from my many contacts." or "This antenna works better than this other antenna I haven't tested and you haven't used." Right now, the subjective testing in this article is fine for saying "this helically wound loop is a GOOD ANTENNA and one worth trying." I'm fine with that. But the article also claims it's working like a bigger loop, and there's no theoretical justification or experimental justification for that, and you can't test that just by making contacts. I would be fine (or at least better) with subjective A/B testing of the two loops, but we can't expect anyone to buy TWO vacuum capacitors for that, plus two magloops in one backyard is exactly the same as those wireless power transfer devices that have been talked about in the tech press in the past few years ;D

=====================

Anyway, it seems to me that some hams think that theory is flawed because they're surprised at how well their antenna works on the air. I think that the people who go on and on about theory in the forums often ADD to this problem by using deep hyperbole to describe everything.

They predict that something is 6dB down from a dipole and they immediately pronounce that it's a "dummy load." They say things like ridiculous things like "CONTACTS are MEANINGLESS," or "GOOD SIGNAL REPORTS are MEANINGLESS" when even the most theory-geek of us usually care about making contacts on the antennas we make and getting subjective reports that we have a good signal. Every one of us, no matter how much we like to calculate things, uses on-air signal reports as part of our test procedure and we all know something is wrong if we're suddenly getting S6's instead of S9's.

The fact of the matter is that if you're 6dB or 10dB down from a dipole or quarter wave vertical, you're still 60dB up from a dummy load. And contacts and good signal reports mean a LOT in the broader context of what we're doing in ham radio.

The thing we need to look at, though, is what are the ERRORS in comparing two antennas on the air vs. comparing them in the backyard or on a better test range **when you're trying to confidently say one is better than the other.**

Like I said to K8NDS (never receiving any response) I built a 4 foot copper pipe magloop, have used it a fair bit on 40m, and got good reports and surprised hams on the other end. But I have no idea (aside from some qualitative predictions) whether or not a helical one would be better or worse. You can't test that without trying them against each other, and for many reasons (accuracy and cost most importantly), the best way to do that is to set up a test where you swap out the helical one for the ordinary one while measuring the difference with a field strength meter.

 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by VE3EFC on August 18, 2011 Mail this to a friend!
Tom states "There has been nothing ... that has shown surface area ... has anything to do with radiation."

At near DC frequency, everyone knows that a thicker wire can carry more current because it has less resistance (less loss) compared to a thinner wire.
The loss is proportional to the cross sectional area of the wire. When we move to RF frequencies, only the outer skin of the wire is used to conduct the current.
Thus the amount of USEABLE copper is proportional to the surface area of the wire, not the cross sectional area. High school calculus tells me that the circle has
minimum perimeter when compared to any other shape of the same cross section area. Thus a round wire or tube is the least efficient (most lossy) shape when it comes to conducting RF current. If you take a round copper wire and pound it into a flat ribbon shape, it will have much more surface area and less loss for RF. Less loss will result in better efficiency and increased radiation. With large antennas, a few ohms improvement in loss does not have much effect. However with small loops, fractions of ohms can be very important. Some magnetic loops are made with flat bar instead of round pipe.


 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KU5Q on August 18, 2011 Mail this to a friend!
"RE: Helically Wound Linear Loaded Magnetic Loop Antenna Reply
by N3OX on August 18, 2011 Mail this to a friend!
====================

N3OX-In the end, this kind of testing is difficult and boring and time consuming.

====================

Like ur post?

=====================

N3OX-Like I said to K8NDS (never receiving any response)....

=====================

Maybe he didn't know or care?

You have PHD in physics?

N3OX-http://www.n3ox.net/About Me

I've held an amateur license since February, 1995, and upgraded to Amateur Extra in 1999. I got the vanity call N3OX in January, 2006. I've been more or less active the whole time I've been a ham. I've been somewhat more active lately now that I'm out of apartment status and into a house where I am permitted some antennas, but I'm leaving all the apartment-specific information up for the cliff-dwellers out there.

I recently finished my Ph.D. in Physics and am working as a post-doctoral researcher at University of Maryland, College Park.

=============================================

Christ man, give it a rest, it's only a hobby!

Quit making yourself look silly.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 18, 2011 Mail this to a friend!
ku5q says: Christ man, give it a rest, it's only a hobby!

Quit making yourself look silly.

sure, we all would much rather read drivel from ku5q than interesting and stimulating posts from n3ox, w8ji and w5dxp.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 18, 2011 Mail this to a friend!
KU5Q: "BSEE UT Arlington, TX-1986. Morse is the only interest that keeps me in ham radio. For me, music is much more fun, interesting, and profitable."

you have a BSEE??

go play your banjo and leave the amateur radio technical discussions to others.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K1QAR on August 18, 2011 Mail this to a friend!


By the way --

The program rjeloop2.exe calculated ground loss resistance as being more than the ohmic conductor resistance when using 3" aluminum tubing with the bottom up 15 feet. Calculated radiation resistance of a 12 footer was .05, ohmic .04, and ground resistance was .06 ohms.

It gets better. With a vertical loop above ground, does it make a difference if the high voltage part (capacitor) is at the top or at the bottom? Measurements on 75 meters, using my mobile as a standard, indicated a 12 footer with the cap on top was consistently 3-4 S units better than the mobile, while the 15 footer in the tree was barely 3 S units better. Both loops' bottoms were about 15 feet up. Use of the mobile nearby each loop should largely have cancelled any site differences, such as ground conductivity, obstructions, etc.

So builder beware! Height and cap placement apparently matter.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 18, 2011 Mail this to a friend!
"by VE3EFC on August 18, 2011 Mail this to a friend!
Tom states "There has been nothing ... that has shown surface area ... has anything to do with radiation."

At near DC frequency, everyone knows that a thicker wire can carry more current because it has less resistance (less loss) compared to a thinner wire.
The loss is proportional to the cross sectional area of the wire. When we move to RF frequencies, only the outer skin of the wire is used to conduct the current.
Thus the amount of USEABLE copper is proportional to the surface area of the wire, not the cross sectional area. High school calculus tells me that the circle has
minimum perimeter when compared to any other shape of the same cross section area. Thus a round wire or tube is the least efficient (most lossy) shape when it comes to conducting RF current. If you take a round copper wire and pound it into a flat ribbon shape, it will have much more surface area and less loss for RF. Less loss will result in better efficiency and increased radiation. With large antennas, a few ohms improvement in loss does not have much effect. However with small loops, fractions of ohms can be very important. Some magnetic loops are made with flat bar instead of round pipe."

xxxxxxxxxxxxxx

Your answer is meaningless in the context of what I said. I specifically said ***radiation***, and now you are talking about ***loss resistance***.

So let's look at loss resistance:

Loss resistance is proportion to length, resistivity, and the cross section carrying current.

What happens at radio frequencies when we change from a round smooth conductor to a wide strip? Current moves toward the edges of the strip, making the center areas have less contribution to cross section. This why a loop with a round conductor of the same surface area and material has a little less resistance per unit length than the flat strip.

The AEA loop using a flat strip, for example, measured higher loss resistance than the MFJ loop. (I actually measured both.)

Second, a longer conductor of a given current distribution, material, and cross sectional area will have more loss resistance.

What does NOT increase, in a given spatial perimeter as we wind a conductor into more length, is the very desirable ***radiation resistance***. This is because electromagnetic radiation in not tied to surface area or cross section, it is all about the ampere-feet over linear spatial distance.

Surface area has no bearing on EM radiation and true radiation resistance. Radiation comes from the linear area of space and the current distribution in that area. If we pack more and more conductor length into a given spatial area, we still have the same area so far as radiation is concerned.

If it was any different than that, we would find coiled up dipoles and verticals in common use. Why waste the space? Over the past 100 years or so, that has not happened for good reason.

What we do find, for the true high efficiency compact antennas, are the most uniform current and minimum conductor lengths in an area of space.

Packing 500 feet of conductor in a three box gives us the EM radiation of a three foot box, and potentially the heat losses of 500 foot of conductor. It is never better than a 3 foot box for EM radiation, although we sure can move bandwidth and loss resistance all over the place, and generally the bad things get worse rapidly when we use more conductor length than needed.

73 Tom
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by VE3EFC on August 18, 2011 Mail this to a friend!
Thanks Tom. I have always believed a flat shape has less loss than a round shape. I thought that is why some high Q coils are wound using flat copper. I see what you are saying - the skin effect chases the useable copper into the corners of the rectangle, so the round shape is actually better. My belief that flat is better will now be deleted from my internal hard drive. I have learned a lot from this discussion.

Just curious, how did you measure loss on the two mag loops? Did you look for heat?

73, Doug
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by AE6RV on August 18, 2011 Mail this to a friend!
W8JI posts: "1.) With a compact antenna, we have to be very careful the feedline is not acting like part of the antenna. There have been many antennas, the EH antenna, the CFA antenna, and many others that unknowingly relied on feedline radiation to be a major part of the radiating system."

Tom, given the parameters of the audience for this antenna: CC&R restricted hams, what would likely be the best tunable contraption to stick on the end of the feedline when the feedline is about all you can put up. Yeah, I realize it's sort of a silly question, but often the feedline doesn't get noticed; it's the antenna that causes the problem.


 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 18, 2011 Mail this to a friend!
by VE3EFC on August 18, 2011 I thought that is why some high Q coils are wound using flat copper. I see what you are saying - the skin effect chases the useable copper into the corners of the rectangle, so the round shape is actually better. My belief that flat is better will now be deleted from my internal hard drive. I have learned a lot from this discussion.

Just curious, how did you measure loss on the two mag loops? Did you look for heat?

73, Doug>>

I measured relative field strength of both antennas, then I replaced the round conductor of the MFJ with a welded in flat strip the identical surface area as the outside of the MFJ loop tubing. This used the same capacitor and feed system with only the conductor changed. As I recall it was just over 1 dB less field strength but that was 20 years ago(???).

The results tracked with calculations of resistance increase with a flat strip. A flat strip decreases inductance but increases resistance.

As for flat vs. round and resistance, textbooks dealing with skin effect repeatedly state current is distributed in a way that encircles the current path with the fewest flux lines. When we think of a flat thin strip very wide strip, that would move current out toward the edges. A round conductor is more evenly distributed provided nothing is close to push current away (parallel flow) or move it closer (opposing flow).

A flat strip at higher frequencies starts to behave more and more like two parallel conductors with wide spacing, or at least a current null, in the middle. I believe Terman has details on this early in his Radio Engineering, and perhaps Kohler and others.

As for high Q coils, edge wound inductors I have measured are very high Q. The interactions in an inductor are quite complex with distributed capacitance, flux coupling between turns, and many other things having an effect. I'm not sure how valid any round to flat comparison would be because several things would change at the same time. Plus the effect that causes current bunching is related to distribution of the magnetic field, and I'm just not sure how that works in a complex system like a large inductor. I do know copper tubing coils are just as good or potentially better. I have seen some copper tubing coils over 1000, and some edge wounds in the 600-800 range (well below self-resonance).

The main reason I use edge wound is because I either have them, or it is easier to get a tap on them without shorting to the adjacent turns.

I think the telling thing is all of this is where we see helically loaded antennas, and how well they really compared to more optimized lumped loading.

When the Navy wanted the most efficient compact monopole that was frequency agile, General Dynamics came up with a hairpin monopole loaded with vacuum variables. We really don't see helically loaded antennas except in rubber ducks, CB antennas, and some Ham antennas.

My guess is that's because antenna designers understand the science better than most home experimenters, and commercial designers also verify results with reliable test methods not found in home, Ham, or especially CB applications.

73 Tom



 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 18, 2011 Mail this to a friend!
by AE6RV on August 18, 2011 Mail this to a friend!
Tom, given the parameters of the audience for this antenna: CC&R restricted hams, what would likely be the best tunable contraption to stick on the end of the feedline when the feedline is about all you can put up. Yeah, I realize it's sort of a silly question, but often the feedline doesn't get noticed; it's the antenna that causes the problem. >>

If I wanted a compact single band antenna I would use a capacitance-hat terminated element with a good lumped inductor.

If I wanted a multiple band continuous tuned, I would use a loop. The loop would be the largest physically enclosed area I could manage using a traditional style conductor with the lowest self-inductance and loss resistance. I would not gamma match it unless I wanted feedline radiation problems, and I would keep the high voltage end up in the clear away from the mast and feedline.

I played with several feed methods in the MFJ loop and the small "link" loop had the least common mode on the feeder by far. Shielding it made no difference. A direct feed with a gamma was far too critical for electrical balance around the HV end of the antenna, where the capacitor is.

As for intentionally exciting the feedline shield, why do it accidentally? Just make it the antenna if that is what it has to be. Doing that, there is some option of controlling where current actually goes.

73 Tom
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 18, 2011 Mail this to a friend!
AE6RV
I said that I wasn't going to answer any more of these unqualified remarks but you don't have an email posted so I just couldn’t resist this one.
I am trashing most of the responses because they are so ridicules.
I am not pointing this at you, you quoted one of Tom, "the know it all" claims that I couldn't help respond to.

Feed Line Radiation:
I can't help it but a whole group of us on the air are still laughing at that one; thank you Tom for making my day! I may be laughing for many days to come now.
I am going to run out in my yard tomorrow and put up a 7 ft piece of feed line running up a 7 ft pole with a dummy load at the end. Tom you just solved all the antenna issues in the world. Man you can put all the antenna manufactures out of business, talk about a cheap solution! If you observant critics haven't noticed there is only about 7 ft of coax cable in the vertical position then it is chocked off with a coaxial balun; by the way I already answered this in the past posts. I have put a very accurate sniffer (calibrated in a TEM cell) on the end of a long arm. There is very little radiation from the 7 ft part and none detectable from the coax by the way that is BuryFlex and goes directly into the ground below the antenna. Man I have really stumbled on something here with this coaxial antenna in which 95% of the coax is buried while it works DX with 5/9 reports on a regular basis! I have to contact VK4TUX and tell him that when I called him and he gave me an S-9 + 10 signal report on 40 mtrs (twice now) that it was mostly radiating from a 7 ft piece of coax (.007 wavelength on 40), he is really going to be impressed now! I might contact a few of the KL7's in which I had the same experience with; everybody needs to know about this. I will direct them to you TOM because I can't explain it, it is beyond my comprehension.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by AE6RV on August 18, 2011 Mail this to a friend!
"If I wanted a multiple band continuous tuned, I would use a loop. The loop would be the largest physically enclosed area I could manage using a traditional style conductor with the lowest self-inductance and loss resistance."

Thanks for reminding me. I had a chance to meet Clarence Moore at his home in Elkhart, Indiana back around 1975 or so. He gave me a 4:1 balun and advised me that the best all around antenna I could put up, given housing restrictions, was a loop of wire around the house as large as I could make it. In those days we called that a lazy quad. I'm sure he was prejudiced, and it's not practical for everyone. I have no way of comparing it to Rich's antenna.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 18, 2011 Mail this to a friend!
K8NDS "you quoted one of Tom, "the know it all" claims"

You are incapable of comprehending tom's point. You are unable to stop the name calling! You are unable to make a cogent argument. You said you were going away, so please just go away.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W7SMJ on August 18, 2011 Mail this to a friend!
KU5Q Says:
Christ man, give it a rest, it's only a hobby!

Quit making yourself look silly.

-----------------------------------------------------

Some of us are trying to learn something and appreciate the discussion...

73,
Scott
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by KG4BFR on August 18, 2011 Mail this to a friend!
Very well done Rich.
Please check out my Loop @ qrz.com
73
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 18, 2011 Mail this to a friend!
K8NDS said:

"I have to contact VK4TUX and tell him that when I called him and he gave me an S-9 + 10 signal report on 40 mtrs (twice now) that it was mostly radiating from a 7 ft piece of coax (.007 wavelength on 40), he is really going to be impressed now! I might contact a few of the KL7's in which I had the same experience with; everybody needs to know about this. I will direct them to you TOM because I can't explain it, it is beyond my comprehension. "

Let's ignore the unnecessary personal insults and misquotes, and look at what you (K8NDS) just wrote. You said 7 feet was .007 wavelengths on 40. It is not. A wavelength on 40 is not 1000 feet.

7 feet on 40 meters is .05 wavelengths. You are off by a factor of 7 times. .05 wavelengths is about 18 electrical degrees long.

http://www.w8ji.com/radiation_resistance.htm

The radiation resistance of 7 linear feet of conductor on 40 meters, top loaded, is about 4 ohms.

The radiation resistance of a 6 foot diameter loop on 40 meters is about 0.07 ohms. Rrad = (3.38×10-8)*(f²A)^2

Note the formula for radiation resistance is based on area enclosed by the loop, NOT conductor length. This goes back to how antennas work. Radiation is by spatial area, not by how much wire we pack into that area.

For the same applied current in each, a 7 foot long linear conductor end-loaded will radiate 57 times the power of the six foot loop.

Further, I never said YOUR antenna is mostly feedline radiation. If you actually read what I wrote, I was discussing EH and CFA antennas. My point was this; it is very easy for any small antenna to have more radiation from common mode on the feeder than it is actual radiation from the antenna.

I do think this radiation resistance comparison is worthwhile in demonstrating how we should to be careful what we do with feedpoints on small antennas, because with the SAME 40 meter band currents, a 7 foot long feedline shield will radiate 57 times the FS of a small ~6 foot diameter loop.

By the way, I can regularly get over S9 reports at 10,000 miles from my mobile on 40 with an 8 foot tall antenna. I'm not amazed by a S9 plus reports from small antennas.

73 Tom




 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 18, 2011 Mail this to a friend!
Your very sharp and definetly correct on that one.
I guess you never slip with the calculator; all my calculations must be wrong. Sorry, I won't do it again. A bit too much caffeen this morning.

Since 7 ft of coax can radiate so well from a shield, I guess it would be fair to make an antenna like that to use for a comparison.

I guess the fact that mine may be raditaing substantually from the coax, that must be why I notice a 3 to 4 s unit difference when I rotate it (not much just 18 to 24 db)?
I guess that if I have such a poor match and cable radiation that would tend to mess up my pattern?
That must be why I get a 40 to 50+ db null (measured by the way) off broadside to the loop in only a very narrow beamwidth. Darn all these confusing technicalities!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 18, 2011 Mail this to a friend!
==========================
WB4JZY says:
"go play your banjo and leave the amateur radio technical discussions to others. "
==========================

No need for that.

I don't mind criticism. Maybe my posts are boring KU5Q; they're probably boring others (and making some people mad) and they're probably too long. Most importantly, KU5Q is absolutely right that I shouldn't have added the remark about K8NDS not responding to whether or not I should swap my copper pipe for a helix. K8NDS has no obligations to respond to any comments. My remark about K8NDS's lack of response was, in fact, made partially out of annoyance about how K8NDS was responding in this thread. As such, it's a backhanded personal attack. And it could be construed as some sort of condescension on my part, like his arguments are invalid if he doesn't respond, or like I'm too important to respond to. It was not meant that way.

I apologize if my comments seem condescending or nitpicky or disrespectful. They're not intended to be that way. Internet forums are tough for this stuff. Easy to get wrapped up in some combination of a technical point you're trying to make and annoyance with other comments, etc.

A magloop is otherwise a really good multiband choice for the HOA crowd. I just expect that a helix winding probably hurts a magloop's performance, not helps it.

If people want to criticize me for saying that without having actually done the measurements myself, that's justified. If they want to criticize me for taking my hobby too seriously, that's fine too. I'll consider the comments and act accordingly.

I've seen worse. Sometimes people tell me to stop living in theory-land and go build a couple of things. Once someone told me I probably can't wipe my a** without the instructions on the toilet paper; that I'm very good at throwing out mathematical equations but can't put anything together and make it work. I can't understand why someone would say stuff like that without first looking at my webpage to see all the stuff I've built in the last five or six years.

Being told I'm writing things that are long and boring and that I take things too seriously is at least kind of useful to me and I can see why someone would write that. There's evidence that's consistent with that idea sitting right here in this thread. It's a valid opinion offered about something that's actually a matter of opinion. Seemed a little harsh, but it seems to have been triggered in response to something that I said that was pretty rude. I should make it clear that I think innovation and learning are completely stifled if we can't talk candidly about disagreeing predictions and observations, so I don't think that chiming in here was FUNDAMENTALLY rude. But certainly some of the other stuff I said and the way I said it was rude.

For the rudeness, I certainly apologize.


 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 18, 2011 Mail this to a friend!
by K8NDS on August 18, 2011

"Your very sharp and defentely correct on that one.
I guess you never slip with the calculator; all my calculations must be wrong. Sorry, I won't do it again. A bit too much caffeen this morning."

Let's not be overly dramatic. :-) Calculators, spell check, who really cares?

"Since 7 ft of coax can radiate so well from a shield, I guess it would be fair to make an antenna like that to use for a comparison."

That comment doesn't sound like we are communicating. I'm not sure at this point if you didn't read carefully, I wasn't clear, or you are just kidding around with me.

"I guess the fact that mine may be raditaing substantually from the coax,"

Of course you know I NEVER said that. As a matter of fact I took extra time to remind you I was talking about the EH and CFA antennas. So again I'm not sure if you are not reading carefully, I'm not writing clearly, or you are just kidding around.

My point is it is pretty easy, when we have small antennas, to have the feedline radiate more than the actual antenna.

"that must be why I notice a 3 to 4 s unit difference when I rotate it (not much just 18 to 24 db)?
I guess that if I have such a poor match and cable radiation that would tend to mess up my pattern?
That must be why I get a 40 to 50+ db null (measured by the way) off broadside to the loop in only a very narrow beamwidth. Darn all these confusing technicalities!"

As I said to another person, we need to be careful of common mode when evaluating small antennas. I wasn't even talking to you or about your antenna.

As for your antenna, I have no idea at all how well it really works. I don't know if it is 10 dB down from a good small mag loop, or 1-2 dB up from one. Nothing you said indicates anything other than it radiates and obviously makes you happy.

As for the null depth, the typical skywave null depth I measured on small loops with clean feedlines was about 10 dB. Groundwave null was very deep, but not sky wave. 3 dB beamwidth is pretty wide on a small loop, and the null is not deep except through the axis (which is generally at zero degrees elevation).

When you measured nulls on groundwave, what angle were the nulls at in relationship to both sides of the antenna?

The only thing I really pointed out was the helical winding and surface area has nothing to do with making the loop look larger from the standpoint of radiation. Why all the fuss?

73 Tom
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 18, 2011 Mail this to a friend!
N3OX "I don't mind criticism. Maybe my posts are boring KU5Q; they're probably boring others (and making some people mad) and they're probably too long....."

oh man, it saddens me to see this post. Please don't take to heart some of the nonsense on here. You are one of the best purveyors of technical knowledge on eham. No one could find any rudeness in any of your posts. Don't change anything! 73
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 18, 2011 Mail this to a friend!
=====
WB4JZY writes:
"No one could find any rudeness in any of your posts. Don't change anything!
"
=====

Look, I've seen Terry KU5Q rip into other people and at those times I didn't necessarily agree with his approach but I probably agreed that the person deserved it in one way or another. I don't mean to upset people and if someone gets upset, communication breaks down.

In a lot of ways this is a TERRIBLE medium for technical discussion because once you start on the discussion you can't just let things sit for a week or two while you think and work quietly on your argument a little at a time, not if you want to contribute anything further. You feel like you're tacitly agreeing with something you don't agree with if you don't contribute something else. Add to that the weird social situation we're in because we're missing so many important cues we'd have face to face but don't have time for editing and private discussion to help catch problems in our tone. It's just a recipe for making people mad and shutting down discussion.

On the other hand, an open forum is a GREAT medium for discussion and disagreement because it allows mildly interested people to lurk and read and think. It also compels people to keep talking, to keep publishing stuff, to keep thinking, and to keep working. It's a very vital medium. Because it's a public discussion, it potentially introduces you to things you never would have gone to look for or were too timid to ask about. It drops new ideas in your lap.

I think that there's a lot of weirdness but a lot of promise in this medium and it's worth thinking about how to maximize the good discussion while minimizing the bad effects. Some people will occasionally get mad at something too weird or trivial to prevent, but sometimes people get understandably ticked off at the tone of discussion and the things that seem to be implied. Public criticism in instantly published print is a really thorny thicket. Some of the problems could be prevented if people were quicker to critique themselves in terms of how they said things and all the possible interpretations. Some people probably think that's a waste of time, but I don't.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 19, 2011 Mail this to a friend!
n3ox:

reading between the lines I sense some angst in your comments and I hope it does not influence your postings. I have an advanced degree in computer science and have met many of the same ilk as the main offender in this thread. In my opinion, the resentment and negative personal attacks stem from an inferiority complex due to the lack of education. Any in depth discussion about the "technicalities" brings out their worst. Its best to ignore them, but the way tom has been attacked in this thread moves me to respond.

Anyway, please don't expend your energies trying to tiptoe around these types, cause I fear it may stifle your technical contributions. 73
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB4JZY on August 19, 2011 Mail this to a friend!
this is interesting:
http://www.hlmagneticloopantennas.com/

wonder if this threads technical discussion has affected any future plans??
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 19, 2011 Mail this to a friend!
It's too bad things are not peer reviewed before publication. That would prevent any perceived or real embarrassment.

Post-publication review creates a lot of ill will, and also once bad information is published it lasts forever.
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by NV6R on August 19, 2011 Mail this to a friend!
I have worked Rich on 40m from my mobile a couple times now. I am very impressed with the performance of his loop. I know to say anything about signal levels is relative, but his were quite strong -- 20dB over 9, which is very strong on my TS-480's conservative S-meter. I have a very good mobile installation -- Scorpion screwdriver with a monster caphat/cage loading; producing around 40% efficiency on 40m -- but to take my S-meter much beyond 10dB over S9 is not easy, no matter what you are using!

Any-which-way, Rich, your loop works, so that is what counts. I am always surprised at how well the magnetic loops perform.

73, John, NV6R
East Central Nevada
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by STRAIGHTKEY on August 19, 2011 Mail this to a friend!
W8JI: You're asking for technical peer reviews? Articles don't even get spell-checked here.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by DJ0IP on August 19, 2011 Mail this to a friend!
I have used magnetic loops, both home brew and commercial versions, on and off for 25 years. To everyone who says the laws of physics can't be tricked, I would suggest you take your nose out of the books long enough to make a trip to your local hardware shop and build one of these. AFTER your have tried it, you might just have a different opinion. They work. They are no substitute for a full size antenna, but a vast number of hams would not be on the air with good signals if not for antennas like these.
With the magnetic loop, there is really no excuse for not getting on the air due to antenna restrictions.
73s; Rick, DJ0IP
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 20, 2011 Mail this to a friend!
"by DJ0IP on August 19, 2011 I have used magnetic loops, both home brew and commercial versions, on and off for 25 years. To everyone who says the laws of physics can't be tricked, I would suggest you take your nose out of the books long enough to make a trip to your local hardware shop and build one of these. "

I'm not sure what you are saying. Are you actually trying to say the small loop violates the laws of electromagnetics and circuit theory governing all other systems in the world?

You are saying that the masters from the 1800's until today never caught the idea they are wrong?

Or are you saying Ohm's law and other things are invalidated by magic?

"AFTER your have tried it, you might just have a different opinion. They work."

You won't find a single post here, NOT one post, where anyone said they can't or don't "work".

" They are no substitute for a full size antenna, but a vast number of hams would not be on the air with good signals if not for antennas like these."

You won't find one post here where anyone disagreed with this, except the author. The author at:

http://www.youtube.com/watch?v=2YpyLAULKqg

posted this:

This magnetic loop antenna is about 50% smaller in diameter then a text book magnetic loop. The performance is outstanding, it compares or is better then a 1/2 wave dipole mounted 1/2 wave above ground. It is also directional, when turned with a rotor it quite often changes around 10 to 12 db from the plane of the loop to broadside.

He also claims he can reduce size without loss in efficiency.


It is not the fact small loops work that is the issue or error. The error is the author thinks, by spiraling a conductor, something half size diameter (1/3 the volume of space) of a traditionally size small loop will work the same OR BETTER THAN something properly constructed that is a full size dipole.

His comments disagree with your comments, so it appears you disagree with the author's exaggerations.


"With the magnetic loop, there is really no excuse for not getting on the air due to antenna restrictions.
73s; Rick, DJ0IP"

That's correct. But anyone who things he can reduce diameter by half, or that a small antenna will beat a half wave dipole at 1/2 wave above ground, is mistaken.

Anyone who also claims by coiling up more conductor area in a smaller enclosed volume of space is also mistake. That is NOT how electromagnetic radiation works.

As a matter of fact, the claims and test methods are very unscientific at best and borderline hoax at worse.

Note none of this is saying a small loop can't make contacts, just that the claims, theory, and test methods are false.

73 Tom






 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KC8VWM on August 20, 2011 Mail this to a friend!
Just made a cheap HF vertical from some wire and a 20 ft. long crappie pole. Seems to exhibit predictable results.

What performance advantage results would a mag loop exhibit over this by comparision?

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 20, 2011 Mail this to a friend!
Just to finalize this post, I received a response from a gentalmen that I beleive knows more concerning magnetic loops then any other infortmation that I have evre run across. In fact if you read his articles they mimiic the results that I have been getting eith my loop design. The foolowing is the QUOTE from VK5KLT:

Dear Rich,

Thank you for your kind words about my mag loop paper; much appreciated. I receive a good deal of nice feedback on that tutorial style article and folks regularly tell me they value the kick-start in the right direction by focusing them on the salient points of loop design and construction, and sorting the “wheat from the chaff” with assimilating the immense abundance of mag loop info’ on the internet.. My primary objective in writing the plain language overview paper was to dispel a lot of the myths and folklore mystery in ham radio circles surrounding the oftentimes underrated and maligned STL antenna.

I presume you have read the latest pdf version of the paper that’s posted on our club web pages:

http://www.ahars.com.au/

http://www.ahars.com.au/htm/Papers.html

Your will also enjoy the excellent slide presentations from my old friend Mike Underhill G3LHZ also posted on the above pages.

I really thoroughly enjoyed looking at your wonderful qrz.com page and your associated STL web page / http://www.hlmagneticloopantennas.com/

Many thanks for bringing them to my attention……it is the first time I’d heard of somebody deploying helical linear loading / distributed inductance techniques on an STL, although I’d often contemplated trying it!! It is a great means of further compacting their diminutive size compared to that achieved with conventional copper tube without significantly compromising efficiency….in fact the pragmatic trade-off in IR loss for an increased BW is beneficial. I concur that you have evolved a legitimate practical technique for compacting an STL particularly beneficial on the lower 40/80/160m bands; great stuff! Your reported Q values speak for themselves…..I like the way you have cleverly exploited conductor skin effect and RF skin depth of flat planar Cu strap. That associated distributed inter-winding capacitance is storing a lot of Q boosting reactive energy and likely flattening out the circumferential current distribution and tending to raise the loop’s net radiation and thus offsetting the rise in IR loss. This probably explains your observation of there apparently being no discernable performance difference vis-à-vis the larger loop diameter with conventional solid Cu tube construction.

Whenever we make an antenna shorter, antenna current has to increase to radiate the same power. If we spiral a full-size antenna up in a tight helix or fold an antenna back on itself, current has to increase to radiate the same power. If we compress the current into a small linear physical area, current has to increase to radiate the same power as that of uniform current flowing over the same area. This is because we have fewer spatial metres, so we need more Amperes of RF current to radiate the same power level. I’ve attached a couple of posts to the Yahoo Magloop reflector forum that touches on this subject that you may find pertinent.

As regards to localized E field noise immunity one has to be very careful to control / choke-off common-mode currents on the feeder coax producing spurious pattern lobes which might be giving misleading impressions of the loop null sharpness that you report. In theory the loop’s distributed capacitance ought to impart a worsened rejection of largely vertical polarized local E field noise….that aspect puzzles me somewhat.

If not already familiar, you might also find it interesting to navigate around the Ciro Mazzoni / I3VHF website of compelling interest: download his STL pdf manual; serious mag loop antennas aimed at amateur and professional radio comms applications.

http://www.ciromazzoni.com/English/Loop%20Antenna.htm

I’d made extensive in-depth studies of electrically small antennas over many years. In case you’re wondering I obtained my longstanding interest in and understanding of electrically small and magnetic loop antennas during an earlier part of my illustrious career after graduate school in the 1980s I used to work with the late and great John Dunlavy Jnr. founder of Antenna Research Associates (ARA) in Beltsville Maryland . John was a terrific mentor in my electromagnetics education and I cut my teeth on antennas of a diverse kind during that formative phase. Among other things, we used to design and build magnetic loops and all kinds of esoteric antennas for the US defence department / NASA / NSA / military / signals intelligence / ELINT / TEMPEST signal reconnaissance community. At Duntech Technetics group we even designed and sold bespoke antennas to Defence Signals Directorate / DSD in Canberra as well as Foreign Affairs Dept / diplomatic embassies.

Like Mazonni’s company in Verona Italy , ARA still to this day produces STL products for military / Navy ships, satellite back-up long haul backbone government HF comms, etc. Some models are rated to kW power levels and designed to be field-deployable and withstand hostile battlefield tactical conditions. I then acquired a PhD and designed and deployed novel magnetic style and other efficient “miniature” H-field antennas for the next 25+ years in the field of radio frequency identification (RFID) passive transponder systems, an area in which I specialised in and still work in with my Adelaide based international R&D company, Invertech Electronics Pty Ltd. This period included a stint as an expatriate visiting professor at the University of Singapore during which time I was also consultant to the Singapore government in defence signal electronics and secure communications and was subsequently appointed Technical Director with defence electronics R&D contractor Singapore Technologies for a while before returning to Australia in 1999 to focus solely on RFID technology and CMOS IC design / development which became my professional forte.

Ham radio is a fun hobby pursuit I occasionally mess around with for relaxation in my precious little spare time. That balance will eventually swing around when I eventually transition into semi-retirement one day; I see that you have already acquired that status of having plenty of time to play with antennas :-) I’m pleased to hear you report your practical experiences with small loops are consistent with that behaviour described in my paper.

I’ve cc. copied this communiqué to fellow AHARS club member Jim Tregellas VK5JST/TR who has developed a keen interest in STL construction and has consequently done some great work on simple but efficacious stepper motor based loop automatic tuning systems for achieving rapid tuning in mono-band configurations. You and he might wish to compare notes

Anyway Rich I hope that my brief comments are helpful / food for thought. Thanks for reaching out and providing the feedback and alerting me to your novel design approach.

73

Leigh
VK5KLT
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8NDS on August 20, 2011 Mail this to a friend!
I wrote this for a to reply to another stations questions, although it fits to answer yours:

Thank You, and all your assumptions are correct.
Some of the many reasons that I state that it works better then a 1/2 wave dipole at 1/2 wave height are:

+ MOST stations cannot rotate a 40 meter dipole at 1/2 wave off the ground, thus not capable of the two s-units that mine almost always (at low angles of radiation) gets.

+ Plus the two S units allows for a good side to front reducing QRM, that again you can't do with a non rotatable dipole.

+ HOA hams usually can't even erect a dipole at even an 1/8 wave above ground.

+Broadside near E field rejection has been a blessing to me, I experience random times of 30 db noise; when I turn the antenna broadside I can completely null it out.

+ My noise floor is always at least 3 to 4 s units lower then any other receiving antenna that I have, making it a pleasure to use. The resulting SNR is always better allowing me to
utilize both of my pre-amps; pre-amps are useless if you are amplifying noise.

+ Lightning strikes which I always have this time of the year do not overload the receiver front end, the power bandwidth of the energy is limited to the narrow bandpass of the antenna. This makes or breaks many of my QSO's on the low bands when there is lighting in the area surrounding a 100 miles or more.

+ The Magnetic loop exhibits both high and low angle of radiation, thus I notice and receive stations notice less QSB.

+ Low angle of radiation is in the vertical polarization while high angle is mainly horizontal, sometimes rotating the antenna gives a better signal within 500 miles when the antenna is not in the loop plane due to this.

+ I can work on these antennas on a 8 ft step ladder.

+No extensive ground radial system is necessary for good performance.

+ relatively inexpensive compared to many commercial verticals and such.

+ last but not least my XYL loves these antennas, being stealth; I know some of the hams here don't care what the XYL likes although many do!

I hope this helps,
Best Regards,
Rich K8NDS

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 20, 2011 Mail this to a friend!
Hi Rich,

The only problems I see with you claims are:

1.) You think packing more conductor into a given space improves performance. That appears to be something with increased inductance, or increased surface area. The exact reason sort of "skips around" to various causes.

2.) Your test methods are meaningless so far as substantiating your primary claim. That claim is the helical winding makes the loop work like a much larger loop.

I really don't understand what there is to get excited about, because it is pretty easy to prove or disprove your primary claim using valid reliable techniques.

As for the VK5's comments....I'm sure you if enough people are solicited, there will be some who will not openly disagree with you.

Let me leave you with a thought......

If packing more conductor into a small space really made a compact antenna better, why are log periodics, beams, verticals, dipoles, and the rest better performers when they employ linear straight full size elements? Why, if helically loading antennas is a good loading method, has it not become mainstream since experiments started in the mid to late 1800's?

I'm not saying small antennas "don't work". I'm certainly not saying your antenna, or any other small antenna, won't make contacts.

What I am saying is your measurement methods are meaningless for proving your major claim, and EM radiation does not work as you claim. It's always a good idea to measure what we claim, especially when an idea disagrees with well-established science.

73 Tom
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W5DXP on August 21, 2011 Mail this to a friend!
EZNEC will supposedly model small loop antennas. A quick simulation of a 6' diameter, 2" copper loop, at 20' on 80m yields a maximum gain straight up of about -15 dBi and pretty much omnidirectional.

Question: Can NEC/MOM be trusted to model small loops (or not)? Here's the EZNEC file.

http://www.w5dxp.com/smalloop.EZ
--
73, Cecil, w5dxp.com
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 21, 2011 Mail this to a friend!
=========================
W5DXP writes:
"Question: Can NEC/MOM be trusted to model small loops (or not)? Here's the EZNEC file. "
=========================

Cecil, I think it's fine. I sent you an email.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by G8JNJ on August 22, 2011 Mail this to a friend!
Hi All,

I’ve also played with various loops (and other compact antennas) , and agree with the many valid points that Tom, Dan and Cecil have made.

Most loops work reasonably well.

Under normal ‘on air’ conditions the difference between a ‘good’ loop and a ‘bad’ one would be very difficult to spot.

The difference between a ‘good’ loop employing good engineering practice and a ‘bad’ loop may only be 2 or 3dB, perhaps 6dB at most.

One of the main points raised in this discussion was the ease of construction and cost saving relative to a copper tube loop. I’m not sure this is valid. If I’d spent $300 or so on a decent vacuum variable capacitor I’d want to squeeze every dB of gain possible from it.

A few additional dollars spent on large diameter copper or aluminium tube with welded joints is the way to do it.

Rich - It’s not that difficult to make field strength measurements so why not try it ? A proper comparison between a helically wound, and copper tube loop of the same physical dimensions would seem to be a valid test.

But be warned - this does carry the risk that you may discover that your new design is actually less efficient than you would like it to be – I know as I’ve personally experienced this many times !

However a quick dose of reality helps stop you (and others) from following false trails, even though sometimes it would be much more comfortable to do so………

I'd say to anyone please experiment, but always endevour to back up your findings with proper valid data rather than hearsay evidence. That's how science works.

Regards,

Martin – G8JNJ

www.g8jnj.webs.com
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by AC5XP on August 22, 2011 Mail this to a friend!
I agree with everything Tom W8JI wrote in the beginning of this thread: the objective is to keep the conductor on the loop circumference as short as possible (as this impact loss resistance of the loop which you want to keep as low as possible), while keeping the loop area as large as possible (as this is responsible for the radiation resistance of the antenna which you want to be as high as possible)

So a "thick", as short as possible conductor in a form that resembles a perfect circle as close as possible meets these objectives the best.

But there are other factors that can have a substatial impact on the performance of these loops. For starters; surface roughness of the conductor. Keep in mind all the RF current is flowing at the SURFACE of the conductor due to the skin effect. So if the conductor has a high surface roughness (even when this is a kind of roughness with a fine granularity), this can considerably lenghten the distance the current needs to travel. So make sure you use something that is "shiny", which is a good measure for low roughness.

The other one is the actual surface material. Copper appears to be the material of choice for our loop, but there is a drawback here. When the surface oxidizes, it turns into copper oxide which is a semiconductor, meaning the surface resistance will increase significantly (and the roughness as well!) So the best way to go here is to have highly polished shiny copper, which you then should degrease and paint. This will keep the surface as pure copper, not copper oxide.

Another way to go is to use aluminum. Most people do not realize it, but when compared to WEIGHT, aluminum is actually a better conductor than copper. As an example, if you take two equal wires (equal in length and mass i.e. weight), the aluminum wire will have the lower resistance. If you take two wires equal in length and diameter, the copper wire will be better because it is a better conductor by volume than aluminum. These unknown characteristics of aluminum are also the reason why free hanging high tension wires are made of aluminum, not copper. Weight is a bigger issue in that application than volume.

Aluminum has another advantage: When it oxidizes, the resulting Al2O3 aluminum oxide becomes a perfect insulator. So the surface current will always flow through pure aluminum, even when there is oxidation at the surface as the aluminum oxide cannot conduct anything. This is a huge advantage over copper. (But keep in mind that aluminum oxidation WILL increase roughness of the remaining aluminum surface that is conductive, so that is still a disadvantage)

As we all know, aluminum has a huge disadvantage as well though: Very difficult to solder. Welding is possible but this needs specialized welding equipment emitting noble gasses around the molten aluminum in the weld to keep the oxygen away. This is equipment normally not available to hams.

Another material that would do well is silver. Silver oxide is just as good as a conductor as pure silver, so this would be perfect for an untreated, weather exposed loop (this is also the reason why professional microwave cavities are always silver plated; it is the best material for keeping the Q of the cavity high over time)
Problem with silver is of course the cost and the technical hurtles to silver-plate a large conductor.

So adding it all up, I would go with polished, painted copper.

Let’s now talk about the shape of the loop conductor. After reading the above, one could conclude a large diameter, hollow conductor like a copper or aluminum pipe is the best.
This is only true up to a certain point. If the "pipe" diameter gets too large compared to the loop diameter, magnetic fieldline components start to become perpendicular to the loop surface, instead of parallel to the conductor, the latter being desired, the former not. Magnetic fieldlines perpendicular to a conductor result in eddy currents being generated in that surface, which translates to losses in the antenna as a whole, thus lowering antenna efficiency.
A circular diameter of the conductor will suffer this fate the least, a tape-shaped conductor will do much worse in this aspect (remember the AEA isoloop with the tape-shaped conductor? NOT good!). If you have finite analysis modeling software, you can model this eddy current phenomenon for different conductor shapes in a loop (which is what I once did for the job I had in those days which required us to design effective loop antennas for RFID applications operating a 13.56MHz).

So considering all the above, what would be the best practical design for an effective loop?
Take a large diameter plastic tube (yes, plastic, stay with me!) and form it in a loop shape that is as close to a perfect circle as possible. Then cover the surface of that plastic with as many individually insulated copper wires that will fit on the pipe surface, that all are parallel to each other. Don’t twist them in any way, keep them parallel (and in a single layer) so they each run the shortest distance across the loop from one end to the other.
Lot's of work, but rewarding - and do-able without the need for specialized tools or equipment.

This concept will do several things: We used the ENTIRE surface of the pipe for the conductor; the wires are pure copper but the insulation will protect them from oxidizing, and the "litz" nature of the surface (created by using many parallel, individually insulated wires) will prevent eddy current on the loop surface as a whole.
This should create a loop that will come as close as possible in Q as what the theory prescribes.
Creating multiple layers of the wire surface (in other words, using real Litz wire) won’t bring anything extra because the RF proximity effect will limit the current in the lower layers, so they would be a waste of copper. Keep the wires in a SINGLE layer on the tube surface.

People will say – "All nice and dandy, but Rich, K8NDS antenna seems to do the job! How do you explain that?"
The answer is: I am not saying Rich's antenna won't work; I am saying, it is far from the best that could be done for a loop design in general.
A very well designed loop (for frequencies at 80 and 40 meter) will have an efficiency that is not much better than 25% (it will be higher for 20 and 10 meters).

So let' say I would design a 40-meter loop and my design gets me 25%: 100 watt in gets me 25 watt on the air. Let' say Rich's design gets 10%, meaning he gets 10 watt out into the air. A difference of 4 dB. Less than an S-point....

And there is another thing at work here. Most hams do not realize it, but they are lucky if they actually get 50% of their power into the air even with "normal" antennas like wire dipoles, verticals or even beams. Feedline losses; ground/radial losses; antenna tuner losses; resistive losses; deteriorating coax and joints; it all holds you back. So if I would make a perfect loop antenna for 80 meters having 25% efficiency, my fellow ham is getting at best 50% efficiency with his dipole or long wire. A meager difference of only 3 dB. If you then also consider the fact that the loop antenna works as a perfect high-Q RF pre-selector for your receiver AND is not sensitive to E-field interference (the kind of interference mostly emitted by power lines and electrical equipment), this puts the magnetic loop suddenly in a class of its own.

Loop antennas are fun, when I was younger I made many of them. And Rich K8NDS did a great job exploiting this fun. So this was not written as criticism. But hopefully my thoughts gave you grounds for making an even better loop antenna.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W5DXP on August 22, 2011 Mail this to a friend!
> Then cover the surface of that plastic with as many individually insulated copper wires that will fit on the pipe surface, that all are parallel to each other. <

This may be a stupid question but would the fact that the individual outside wires are longer than the individual inside wires tend to broaden the bandwidth over a single conductor?
--
73, Cecil, w5dxp.com
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K8JD on August 22, 2011 Mail this to a friend!
I can see why you designed this antenna to hold up with a 1.5 KW power input ! With a KW, almost anything metalic will have a great signal on the air.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by NN6EE on August 22, 2011 Mail this to a friend!
Magnetic Loops are rather a life-saver for us! I recently purchased a "Mag.Loop" from "Pixel Technologies" and it's only about 12 ft. above ground and hooking it up to our K3 it has the ability to NULL OUT NOISE here locally which has made all the difference in the world for our enhanced enjoyment of listening on the HF bands especially 160/80/40/ & 30 meters. It is to be used for (receive-only) but with the quick-switching that the preamp has there's no problem with my using for xmit my 80m inverted L and the loop even running 1kw. The size is rather small, being only 1m.in dia.

Considering the past dealing with horrendous NOISE (typical-daily S-8 to S-9) using the loop on receive we're now only bothered by an "S-3" noise level on all of the aforementioned bands!

It's made all the difference in the world on bring back the JOY of using HF on the lower bands and it "hears" GREAT!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K5AF on August 22, 2011 Mail this to a friend!
W5DXP Writes: >>This may be a stupid question but would the fact that the individual outside wires are longer than the individual inside wires tend to broaden the bandwidth over a single conductor?>>

I just purchased a bunch of PVC and 45 degree elbows and was planning to do just what has been suggested. I was going to start with just one #18 silver plated stranded copper teflon jacketed conductor, and then add more one at a time to observe the impact on radiation efficiency and bandwidth. Obviously, the conductors will not all be the same size, but since we're dealing with high and consistent currents, the variations in length probably will not impct bandwidth, or will they?

Excellent discussions and ideas, gents!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W9ZSJ on August 22, 2011 Mail this to a friend!

On Aug 22, 2011, at 4:43 AM, Articles@eham.net wrote:

Quote from Martin G8JNJ: I'd say to anyone please experiment, but always endevour to back up your findings with proper valid data rather than hearsay evidence. That's how science works.

***

From George, W9ZSJ:

I’ve written several responses to this thread, then thought better of posting them. But now that the sound and fury are dying down, I will chip in with my 2 cents.

It seems to me that what we had here was a failure to communicate. What was missed for a long while and which may not have sunk in yet are the last sentences in the post by Martin, G8JNJ, quoted above. Also, the comments by N3OX regarding the peculiarities of this form of communication were quite spot on. The terseness of scientific and engineering discourse without cues or appropriate introduction can steer things off course.

At the risk of making this post too long and boring I share an anecdote. In the early days of packet radio as fostered by TAPR we had a bunch of very competent folks in the Chicago beta test. I was in awe of their competence and enthusiasm. Perhaps our most competent person was one who had a perpetual smile and often chuckled when spoken to face to face. He was an engineer who spoke what he thought but always had technical data or references to back it up. Just for reference, let’s call him Don.

After the local packet network was up and running, lots of less informed folks, ordinary hams, joined the fun. Anyone on packet in Chicago at that time would read Don’s ideas and proposals. I learned a lot from Don. One day a newby appeared on the digipeater with exchanges typed with the caps lock on. (Recall, this was long before email and the web.) Don, in a message I reread for hidden meanings and finding none, sent a message to the newby (for all to see since there was no other way at that time) not to do that and that it looked like he was shouting. The newby took it personally and went away mad and apparently told his friends that Don was a jerk. The ensuing communications for the whole group were muddied by this innocuous event., which certainly would not have happened if the typing advice had happened at a local meeting.

***
I was enamored by the Ted Hart articles on small magnetic loops back when they appeared and I built one then. (Ted’s original article in QST came from his placing in an ARRL antenna contest tor which the final entries were tested on the Hy-Gain antenna range. See QST, February 1985 and June 1986. Also, see the flurry of short articles in Sprat, the GQRP mag, around that time for accounts - no, anecdotal evidence, that small loops work. (My gosh, I just found that old copies of Sprat are actually available! Now I can chuck mine.)

I pulled my loop out of the basement yesterday and set it up, ignoring all rules of good engineering practice. I would like to say that I immediately made several contacts on the front driveway with my 4 watt Ten-Tec rig. Alas, it didn’t happen. It wasn’t a fair test, but I was suckered in by the numerous Youtube videos of hams, mostly in Europe but a notable one in Brazil, casually having SSB QSOs with small loops. I ignored several caveats in my zeal to experiment, but I did identify what I need to do next to save the copper loop. (Nowadays I might have to paint the loop to keep scavengers from realizing that it is copper. And, a later post advises painting anyway.)

In my attempt back then I tried a bazooka capacitor one half of which was integral to the loop. The other side was a smaller tube which slid inside the loop. It worked, giving a capacitance of just a little over 200 pF at max, and my MFJ SWR Analyzer (first generation, not really up to the task) showed me that it tuned on 40 through 20 though the adjustment was so finicky as to be almost useless unless one were at the antenna to adjust it. I did have QSOs with it, all at very low power. Yesterday, by Googling *small loop capacitor* I found half a dozen better ideas to avoid buying an expensive vacuum capacitor for this project. I also found some butterfly and other caps of the right range in the basement which I never tried in the first round of explorations. Time to dust them off. Maybe I will actually get “small magnetic loop” out of the “To-do Queue.”

***

If I were to be involved in a course on the philosophy of science, which easily could have been in my bag of tricks professionally, I might assign this entire thread for analysis and comment, totally apart from its technical content. I might also assign them to look up the thread on eHam about the Crossed Field Antenna and the EH antenna, a somewhat more civilized debate along the same lines. (No surprise to see the name of one of the naysayers there.) That would make for a good “compare and contrast” exercise.

But that wouldn’t be as much fun as checking out those capacitors that I picked up at various hamfests over the years. And it certainly wouldn’t stand up against a few DX QSOs with my 4 watts now that conditions are on the rise. I’ve been getting them with a random long wire made of plastic coated single conductor #20 wire, 7 feet off the ground at one end, that occasionally breaks. I just strip it at the break, tie a knot, and move on. I use a tuner and have never measured any feature of it. It works and I urge it to anyone who doesn't have another antenna to try one like it. But if you have a small yard, try a small magnetic loop.

***
Finally, for those who haven't read it, I recommend the paper by VK5KLT for a good, overall. practical survey of small magnetic loops. There are nice photos and diagrams. It's 22 pages long and is available from the already cited http://www.ahars.com.au It is apolitical. Since the URL is unwieldy, I submit this instead: http://tinyurls/SmallLoops.com Much recommended. for folks who want to build their own.

Also at http://www.ahars.com.au/htm/Papers.html are many earnest, informed, and interesting opinion and some data about similar subjects, mostly the CFA and EH debates alluded to above.

George W9ZSJ
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W4HV on August 22, 2011 Mail this to a friend!
This is the very typical response from TOM. I am not involved in very much restricted space work, but I can clearly say that if it works it must work!.. i got the same response from several E-Ham Guru's when i first started marketing my cage designs.. i am glad that sensible people still exist who want to try new slants on old ideas.. Surprisingly you don't have to conter-market against your competitors to succeed.. But some people think its the way to go.
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by VE3EFC on August 23, 2011 Mail this to a friend!
When discussing the merits of helical wound magnetic loops, it is important to consider the effect of inverse reactive current, which would likely result in unilateral phase detractance. If the helical windings are tighter than the Milford threshold, this would cause a situation where the magnito reluctance will exceed the capacitive detractance. The modial interaction of conductors and fluxes could possibly be reduced by employing the normalized lotus O-deltoid configuration, but this may increase the problem of sinusoidal depleneration. Conductors made from prefamulated emulite would solve most of these problems.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W5DXP on August 23, 2011 Mail this to a friend!
Actually, a small super-conducting loop would beat the socks off of prefamulated emulite. I just haven't figured out how to keep the cooling system from affecting the radiation pattern but I am working on it. In the meanwhile, all I have to show for my effort is a loop with 24 dBi omnidirectional gain.

http://www.w5dxp.com/SUPRGAIN.EZ

Let's see anybody beat that!
--
73, Cecil, w5dxp.com
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 23, 2011 Mail this to a friend!
Cecil you could probably just use styrofoam to hold liquid nitrogen if you used a YBCuO superconductor.

Good luck finding a superconducting capacitor though :)
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 23, 2011 Mail this to a friend!
===================
VE3EFC writes:
" The modial interaction of conductors and fluxes could possibly be reduced by employing the normalized lotus O-deltoid configuration, but this may increase the problem of sinusoidal depleneration. Conductors made from prefamulated emulite would solve most of these problems. "
===================

Prefamulated emulite is so expensive that I would do field strength measurements on unfamulated emulite compared to copper, and then I'd try a home famulation kit if it needed it.

Remember, the skin effect means you only need to have the emulite famulated in a thin layer, not all the way through.

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W9ZSJ on August 23, 2011 Mail this to a friend!
In the interest of precision and since these postings are likely to be here forever, I suggest that some typos in the recent posts be corrected:

Modial - don't you mean modal? Or, is there yet another new conductor interaction to be considered?

YBCuO - don;t you mean YbCuO? I ask because I am considering investing in ytturbium futures. Or, is there a new element, Y, which has just been discovered? Anyone remember Tom Lehrer?

I am biting my tongue to avoid commenting further on what I regard as serious misrepresentations of the technical content of these messages.

George W9ZSJ

Jane, you ignorant slut.
Dan, you pompous ass.
SNL, ca 1978

 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by W0BTU on August 24, 2011 Mail this to a friend!

I may very well build an STL (small transmitting loop) for 40 through 15 meters. I've been modeling different sizes and shapes at various heights in EZNEC+, and plugging different numbers into AA5TB's spreadsheet.

I've waded through this discussion, and one very important thing I haven't seen discussed here was the STL's radiation angle advantages (in many cases), compared to a low dipole or vertical.

Anyway, I'd appreciate some advice. I'm trying to figure out what the current would be through the capacitor on 40 meters on an octagonal STL made from two 10' pieces of 1" Type M copper water pipe. To determine that, I THINK that we need to add the radiation resistance and the copper losses together. (We can then find the square root of P divided by the sum of those two resistances.)

In the spreadsheet at the top of
http://www.w0btu.com/magnetic_loops.html, RR= .084 ohms and Rloss= .047 ohms, total .131 ohms. The square root of 1500/.131 = 107 amps. Is that the current that the vacuum variable will have to handle, or am I doing something wrong here?

(Just ignore the other images on that page.)

TIA.

73, Mike
www.w0btu.com
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 25, 2011 Mail this to a friend!
Mike, I think your math is fine, and that current is what I get from EZNEC for your proposed loop too if it were in free space but I think you probably don't need to actually shop for a 107A-capable capacitor.

If you install it at a small height above ground (say one to two loop diameters) with the loop in a vertical plane, the radiation resistance goes up quite a bit.

You also add in some loss resistance from coupling to the earth.

An EZNEC prediction over "Real/High Accuracy" earth with 0.005S/m conductivity and dielectric constant 13 with the bottom of the antenna up six feet gives about double your resistance number (0.26 ohms) for the total feed resistance of the loop. About 0.045 ohms is extra radiation resistance from putting the loop over ground, and about 0.087 ohms is from nearfield ground loss.

This is the prediction with the feedpoint at the bottom. With the feedpoint at the top, like in K8NDS's loop, the radiation resistance is increased even a little more. However, it appears that low angle radiation is unaffected by that change... just adds or subtracts a couple dB of high angle radiation, but it does affect the total feed resistance and the current. The difference in top feed vs. bottom feed seems to depend heavily on the loop size in wavelengths, because it relies on the loop departing from constant current all the way around. The effect is much smaller on 80m.

Anyway, the added radiation resistance and induced ground loss resistance are probably going to reduce your current pretty substantially... I'm getting like 70-85A depending on soil condx etc. Would be really interesting to directly measure it on the finished loop... though I think the typical toroidal transformer you'd use for current measurements might perturb the loop too much.

Also, unless you plan on running full legal limit RTTY bulletins, you probably can reduce the current rating of the cap.

This might all be moot because a cap big enough to stand off the incredible voltage might easily take 100A+ on a continuous basis anyway ;D



 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W0BTU on August 25, 2011 Mail this to a friend!
Thanks, Dan! :-)

I really appreciate your taking the time to model it in EZNEC. I'd love to have your .ez file, if it's not any trouble.

73 Mike
www.w0btu.com
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W0BTU on August 25, 2011 Mail this to a friend!

> by N3OX on August 21, 2011
> =========================
> W5DXP writes:
> "Question: Can NEC/MOM be trusted to model small loops (or not)? Here's the EZNEC file. "
> =========================
>
> Cecil, I think it's fine. I sent you an email.

I've seen that file before, and I've always wanted to know what W7EL would have to say about that. It certainly shows that EZNEC has its limitations, but loops of the sizes we are talking about here absolutely CAN be trusted, if we keep the limitations in mind.

Here's what the EZNEC 5 manual says:

"NEC-2 is unable to accurately model small loop antennas. If this is attempted, a zero or negative feedpoint impedance and accompanying error message may result. NEC-4 is more tolerant, but problems might still be encountered with very small loops. Double precision versions of both engines permit smaller loops than the standard or single precision versions. Tests with a square loop in free space, one segment per wire, showed reasonably accurate results with loops down to the following minimum circumferences:
NEC-2: 0.05 wavelength
NEC-2D: 0.0005 wavelength (Available in EZNEC+, EZNEC Pro/2 and
EZNEC Pro/4 only)
NEC-4: 0.001 wavelength (Available in EZNEC Pro/4 only)
NEC-4D: 10-7 wavelength (Available in EZNEC Pro/4 only)
These should be used as guidelines only, as accuracy can depend on a number of factors."

I would add that as we approach very close to the ground, the accuracy would be compromised (to some unknown extent), even though our loops here are not small enough to generate an error message in EZNEC.

To me, not modeling a small STL here in EZNEC+ before I actually build one is unthinkable. :-)
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 26, 2011 Mail this to a friend!
"I'd love to have your .ez file, if it's not any trouble. "

http://n3ox.net/files/eznec/magloop_6ft_1in_typeM.EZ

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB6ZRP on August 26, 2011 Mail this to a friend!
Right on Rich!! To many ppl wanna be a smarty pants. I've worked you on that loop and I've listened to your QSO's And the proof IS in the pudding.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB6ZRP on August 26, 2011 Mail this to a friend!
Hi. You missed the point, the loop is for limited space hams and restricted by lame HOA places.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB6ZRP on August 26, 2011 Mail this to a friend!
Aw com-on smarty pants, the loop is just another way of doing it. loosen up, have some fun. I live in a apartment, I use the metal strip around the eves of my building. It realy works great. I get great DX.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB6ZRP on August 26, 2011 Mail this to a friend!
Amen!!!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB6ZRP on August 26, 2011 Mail this to a friend!
Hi. Keep it up Rich. I worked you and have listned to your QSO's. The loop works great in real life. Like my antenna situation. I'm using the metal strip on the eves around my apartment building. I get real results and great DX. I have no idea about the math of why it works or radiation angle or pattern. It has a less than 2:1 swr on all bands on hf. Lame HOA and any antenna restrictions are stupid, in the face of natural disasters ppl will think differently when Hams are the only communications left, ie; Katrina. Us hams have to keep being innovative and always think out of the box. Proof in the pudding is always what counts.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB6ZRP on August 26, 2011 Mail this to a friend!
I got your point totaly. Keep up the good work, many of us do realy apreciate hams like you!!
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W0BTU on August 26, 2011 Mail this to a friend!
by N3OX on August 26, 2011
> "I'd love to have your .ez file, if it's not any trouble. "
>
> http://n3ox.net/files/eznec/magloop_6ft_1in_typeM.EZ

Thanks, Dan. I don't see how you used it to find the current and RR at different heights. Guess I better read some more in the EZNEC manual.

I ordered a big NOS vacuum variable a few minutes ago. I just need to find a toothed pulley for its 12mm shaft.

=========================

by WB6ZRP on August 26, 2011
> Amen!!!

Amen to what? You seem to be talking to yourself. :-)


 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WB6ZRP on August 26, 2011 Mail this to a friend!
Amen!! As I said before, I get your point. I'd build your loop if I could put it up at my apt. Like my ant. situation, using the metal strip around the eve of the building, I would assume it is very ineficient and lossy as it is very broad banded at a 2:1 swr on all HF bands, but like your loop the proof is in the pudding. I get great reports and work alot of DX. I'm sure the math and theary of it's operation is terrible. :=) Hi Hi
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on August 26, 2011 Mail this to a friend!
For the current, the ultimate fate of the power entering the loop doesn't matter. If it's 0.26 ohms over Real/High Accuracy ground with wire loss set to "copper," and you look at the current through the capacitor load, that's the end of it. That's your prediction.

Whether or not it's an *accurate* prediction is another thing: since a healthy fraction of the total resistance is due to induced currents in the soil, and soil is a poorly characterized thing not well described by infinite homogeneous stuff. But that's always a problem with modeling antennas that interact heavily with the dirt, and a very compelling reason to do solid objective measurements.

Trying to figure out the radiation resistance over DIRT is more complicated to explain.

I did a bunch of calculations with copper loss turned on and off, over perfect, MININEC, and Real/High Accuracy ground, and after some accounting, found that the radiation resistance over the Real/High Accuracy dirt agrees with that predicted over a perfectly conducting ground plane. I'd be happy to explain what I did in detail but I don't think a big monoblock of text written this late at night is the right format for it. Basically you have to look at the formula

Eff = Rrad/(Rrad+Rloss) * Fresnel zone loss

for several different cases of Rloss (dirt nearfield loss vs. none, copper vs. none), and it turns out in the case of a small loop Rrad is always the same number, the same one as the loop at that height above perfect ground.

Constant radiation resistance with changing soil parameters isn't a given, so you have to check it. But it works out very well in this case. This isn't too much of a surprise because the current distribution on the loop is simple and just doesn't change much as the soil is changed.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K7DAA on August 26, 2011 Mail this to a friend!
Rich:

Remember this important advice:

ILLEGITIMI NON CARBORUNDUM

See: http://en.wikipedia.org/wiki/Illegitimi_non_carborundum

Don't let 'em tear at your spirit, and make you regret posting this fine article! The world is full of self-important jerks who don't produce original material, but who love to try to aggrandize themselves by riding on the backs of others. I'm sure they are very, very impressed with their own cleverness. The rest of us understand them for what they are.

I am in an HOA restricted neighborhood as well, and have built several mag loops. I've also purchased and sometimes use the MFJ loop, with its neat little control box, and have quite a bit of experience with mag loop design. I fully agree that the proof is in the pudding with these types of antennas. They DO work, and surprisingly well. Would I rather have a full-size dipole at 75 feet? SURE! But I can't even dream of putting one up. Instead, I load my seamless rain gutter or use one of my mag loops.

Thanks for the ideas and photos you presented on mag loop construction--I may try some of your advice on my next design!

In the mean time, those of us who HAVE actually taken the time to BUILD and USE these antennas can just wink and smile at the folks who haven't, but who insist that they are only slightly better than a dummy load.

73, and I mean that sincerely!

Dave - K7DAA
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 28, 2011 Mail this to a friend!
Some of the responses are very odd. Nowhere in this did anyone ever say a small loop cannot radiate, or is "barely better than a dummy load".

Almost anything radiates, and as someone else pointed out the difference between a good loop design and a poor one (like this) can be only a few dB.

The claim however, is that helically winding the element in a loop greatly increases performance. That claim disagrees with long established science.

Not one thing in any article details, or in the ranting that follows, supports the extraordinary claim that helical winding makes a given size loop antenna radiate like it is much larger.

Anyone making an extraordinary claim has some obligation to make some coherent reasonable effort to support their extraordinary claim.

A three foot loop is a three foot loop, and will never act like a six foot loop just because we pack six feet of conductor in a three foot area. Anyone who thinks differently should prove it, because Kraus, Jasik, and all the rest over the years way back to the 1800's should have more than some sloppy S meter reports against unknown reference antennas to prove all the science wrong.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by NN5AA on August 29, 2011 Mail this to a friend!
William, like you I am following this article and the follow-up comments with interest. Your comment about the 'gurus' made me think: If we only did what the 'gurus' said would work, or never tried anything not 'guru approved', where would we be? Not just in the field of Amateur Radio, but in many other areas of scientific endeavor and experimentation.

Can't tell you how many times I've been told through the years, 'Can't be done!" ,'Won't work!", "Doesn't work!"
But stubbornly trying anyway, amazing how many times it did work, could be done, although not 'guru approved'.

 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on August 29, 2011 Mail this to a friend!
Anyone can momentarily look like a level-headed "thinker" or "winner" by inventing an outlandish statement that was never made, and ridiculing what was never said, and attributing his fabricated statement to unknown straw-men called "gurus".

The facts, however, are entirely different. :-)


73 Tom
 
Helically Wound Linear Loaded Magnetic Loop Antenna  
by N0GV on August 31, 2011 Mail this to a friend!
Hello folks,

Here is my take on this.
1) Small loops can function.
2) A small loop that can be erected beats a beam that cannot.
3) There has been no quantative performance testing performed.
4) Directionality is a given for a small loop.

The only documentable advantage in the described construction is that it is considerably easier to add the tuning cap when using a foil than a pipe. Covering the entire surface of the PVC with flashing would have worked even better.

Radiation Efficiency is defined to be the ratio of the radiation resistance to the resistive losses of the entire antenna structure including the matching network. Rad. Resistance of a small loop is really, really tiny! For a 1m per side 1" diameter perfect conducting loop at 14.140 MHz the Rad Resistance is about 0.234 Ohms!!!! For the same diameter Copper pipe you have 0.269 Ohms of total Resistance -- Max efficiency would be 86% IF the feedlines, matching network and ground losses are IGNORED. Use 2mm diameter Copper wire and this goes to 1.052 Ohms total and a MAXIMUM efficiency of about 22% even if everything else is PERFECT!

Effective Aperture -- A 1/2 wave dipole has an effective aperture of about 0.13 Lambda Squared. A small loop has an effective aperture of 0.12 Lambda Squared.... Hey -- that is pretty decent; I guess it is OK there... ;) (http://www.ece.msstate.edu/~donohoe/ece4990notes5.pdf)

Hmmmmm..... Well, lets see, If the loop is fed from the bottom and the plane of the loop is vertical it will be vertically polarized.... The ground losses will be a significant problem..... True -- but all low antennas have that problem so that is a wash....

Now about matching -- we need to get 50 Ohms to match to 0.234 Ohms -- a ratio of 213:1 in Z or 14:1 in terms of turns..... Losses here are going to be significant since we also have about 200-500 Ohms of inductive reactance to tune out. Let's hope that we can match with less than 1dB of loss (fantasy for certain but even 2dB is survivable at 100 watts). Still not too different and sure won't be showing up on an over the air "can you hear me?" test.

Now about the "linear loading" -- does it work? Well 7 Turns of "flat" copper 0.5mm thick on a 2" diameter form will be about 5uH or about 50 Ohms of inductance at 1.8MHz. 4 of those will get you about 200 Ohms MAX! This could help you match. It won't replace the matching network but will help.

Net result -- it will work OK but the result is neither better nor worse than the copper pipe loop. About the same as a short fat dipole....






 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on September 1, 2011 Mail this to a friend!
Effective aperture is a product of gain and frequency.

As such, it must include losses.

Since effective aperture includes losses, it cannot be a constant value for any one size real antenna.

http://www.w8ji.com/capture_area_ae_effective_aperture.htm

For a given loop area, a single turn loop has a fixed radiation resistance. The only variable we can control affecting efficiency is resistance. By adding conductor length in a given physical loop area, we can only increase losses.We cannot ever make path resistance less than the shortest possible length around the circumference for a given resistance of material per foot.

This means if we have a certain size copper flashing or foil, and a certain diameter (enclosed spatial area)loop, radiation resistance is fixed by loop diameter. The only variable important to field strength we can control is loss resistance, and it will be minimum with the shortest possible foil that completes the given outer circumference path back to the capacitor terminals.

We can also change reactance. By increasing conductor length we increase reactance. This increases voltage across the capacitor, increases operating Q, increases stored energy, and increases losses.

The only possible effect of increasing conductor length inside a given area of loop circumference beyond minimal possible length for a given conductor style would be an INCREASE in loss.

Any increase in loss is a decrease in effective aperture or capture area.

While it is true with a lossless loop or dipole capture area is virtually the same, it is NOT true in real life. In real life with loss, effective aperture is set by gain and frequency, and so lossless Ae and not be used to predict a small dipole and loop have similar gain.

As a matter of fact I can build a small dipole of the same conductor length or volume of space that has higher efficiency than the loop. The primary advantage of the loop is frequency agility. It has the disadvantage that in every direction radiation from any area is opposed by radiation from other opposing areas of the loop. This forces radiation resistance down, and forces current up. This higher radiation resistance is why a small dipole can be just as good or even better. The small dipole is just not very frequency agile.

This is how simple and non-complex a system like this works. When we don't invent our own theories, we have the freedom to learn how things really work. Freedom to learn how antennas actually work is what will really let us build a better antenna, not pretend we made one.

73 Tom
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WA3CCI on September 2, 2011 Mail this to a friend!
Without deviation from the norm,"progress"is not possible. Frank Zappa
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W5DXP on September 3, 2011 Mail this to a friend!
Has there ever been an antenna that deviates from Maxwell's equations (the "norm" for ~135 years)?
--
73, Cecil, w5dxp.com
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by WA3CCI on September 3, 2011 Mail this to a friend!
Probably not yet. But maybe soon. Who knows?
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by TURBOBOB on September 3, 2011 Mail this to a friend!
I’m sure that someday we may have “sub-space” communications which are based on a warping of space and that the antennas then may be developed based on that understanding. Until then I will put my money on Maxwell’s equations.

It is interesting that the main design tools for developing low frequency RF signature reduction (stealth) aircraft design use super-computer code to solve Maxwell’s equations for the wave travel over the aircraft surface. Maxwell’s equations – oldies but goodies.

Bob
K9FHY
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W9ZSJ on September 4, 2011 Mail this to a friend!
WA3CCi, W5DXP, et al



It seems to me that the real question is: How will we know?

That would involve reproducible data from a controlled experiment of the kind that has not been forthcoming in this thread.

George. W9ZSJ
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by N3OX on September 4, 2011 Mail this to a friend!
=========================
K9FHY writes:
"It is interesting that the main design tools for developing low frequency RF signature reduction (stealth) aircraft design use super-computer code to solve Maxwell’s equations for the wave travel over the aircraft surface. Maxwell’s equations – oldies but goodies. "
==========================

I think maybe people don't appreciate this. Classical electromagnetic theory is really, really good... and humankind is not done testing it. There are all kinds of scientists and engineers who put Maxwell's equations to the test on a daily basis. They model things and then measure them with equipment that would make any experimentally-minded ham drool. What we ARE finding is new applications of Maxwell's equations that go along with unusual mathematical solutions to them. It is certainly possible to find new arrangements of conductors, dielectrics, and magnetic materials that do new things. An example of that is the electromagnetic "invisibility cloaks" that have been a hot area of research lately.

And there's no fundamental reason why people can't discover new, interesting things just by experimenting. After all, there's no need for a theory for things that haven't yet been observed ;D We run into problems, though, when the experimental evidence for "new thing" isn't enough to rule out a simpler explanation based on what's already known.

If I were to claim that I'd built a metamaterial invisibility cloak tuned to 7.025 MHz around my house so that it wouldn't mess up the pattern of my four square, and then told you it was working because I was easily working DX stations coming "through" my house, I haven't really given you enough information for you to be confident my invisibility cloak design was working. If I instead showed you field strength measurements at a few degrees elevation from twenty different headings around my property, both before and after I built the RF invisibility cloak, and I showed you that there was a 7dB improvement in the "through house" direction at low angles without affecting the rest of the pattern, then it would be clear to all that I was on to something. Narrowband RF invisibility cloaks are a real thing. You can build them out of a bunch of what are essentially small magnetic loops:

http://en.wikipedia.org/wiki/Split-ring_resonator

There's no magical new physics there. Even so, if I were to go through the massive trouble to "cloak" my house at 40m, people would only believe that it was working if I showed them some pretty hard data. Everyone knows that you can work things on 40m "through" your house. Everyone knows that a vertical works okay with an obstruction like that. People also know that there's a big difference between a bunch of copper etched rings on a Duroid substrate in an anechoic chamber and the weird mess of magloops I built around my house, so it would be easy to build a physical system, take lots of photos, show that it was similar to stuff in the literature and still have it not work well or at all. It doesn't matter that I can point to all sorts of theoretical and experimental papers on electromagnetic cloaking.

What people will want to know from me is the dB difference at low angles "through" the house with and without the RF invisibility cloak, and they would want to know the exact procedure by which I arrived at that and what the error was in that number. A a reasonable improvement stated in dB with small error bars and a clearly reported experimental procedure is the thing that would make it worth it to others to actually TRY the technique.

And that's for things that are already established to be correctly predicted by our very successful established theory of electromagnetism. If you have a new theory or if you have an esoteric new solution to Maxwell's equations, the burden of proof is even higher.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by W8JI on September 5, 2011 Mail this to a friend!
by W9ZSJ on September 4, 2011
It seems to me that the real question is: How will we know?

That would involve reproducible data from a controlled experiment of the kind that has not been forthcoming in this thread.

George. W9ZSJ>>>>>>>>>>>>>>>>

Which hits the nail on the head EXACTLY for this article.

There will always be people have a difficult time sorting blind faith or emotion from science and fact, and who don't understand how to do experiments.
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by K1ZJH on September 9, 2011 Mail this to a friend!
Were either of these two questions ever answered? If so, they were lost in the rhetoric and I missed the replies.

Pete


by W5DXP on August 17, 2011 Seems the unanswered question is whether it works better than an all copper loop of the same size and, if so, exactly why? What term(s) in Maxwell's equations would account for that?
--
73, Cecil, w5dxp.com

by K1BXI on August 15, 2011 Mail Rich, did you measure any common mode current on the outside of the coaxial feedline? If you did and found some, how much do you think it may have added to the overall radiated signal. John
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KG4WAT on September 20, 2011 Mail this to a friend!
I remember from my Novice license study guide that Hams are supposed encourage each other and help each other. This is what attracted me to the hobby to begin with. Arguing whether physics allows or disallows certain things hardly does that. Very discouraging hearing this kind of speak among Hams that are supposed to be the helpful kind! Whether it is just an antenna or even whether you are technically correct, your tone is hardly representative of what the spirit of the Ham community is intended to be. Yes you are right, but you are also very unkind! Try a bit harder not to be right but to be kind.

N1AJV
 
RE: Helically Wound Linear Loaded Magnetic Loop Antenna  
by KG4WAT on September 20, 2011 Mail this to a friend!
My post was meant specifically for W8JI. Thought it would post it right under his post when I hit reply in that specific spot. Glad I'm not the one married to him.....

N1AJV
 
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