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Author Topic: TAK-tenna...Really that good/  (Read 4186 times)
AA4PB
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« Reply #30 on: April 09, 2008, 08:05:37 AM »

According to EZNEC, this antenna functions as an unbalanced load that injects large common mode currents onto the feedline.
------------------------------------------------------
This seems to be a common "feature" among several of the tiny antennas. As you say, the problem with allowing the feed line to radiate is that everyone gets different performance, depending on how the feed line is routed. Might be better to just run a random wire out the window and hope for the best. Thats what we used to do years ago. Now we hang a $100 hunk of metal on the end of it :-)


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AJ4DW
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« Reply #31 on: April 09, 2008, 08:35:36 AM »

N3OX (Dan)

Sounds like a plan. I do like your model, thanks for the link. I've already got one end built at home (the crossed PVC supports with notches cut to support the wire), and I'll be starting the other end once I get another two, more pressing, projects out of the way.

Will you be using aluminum or copper wire, and will you try to maintain the smooth spiral (rather than squaring everything off)? If we held the coil loose (no notches) between parallel supports (and if it was stiff enough to maintain it's spacing, or if the supports had foam linings and were held together with rubber bands) we could vary the distance between successive loops to see what effect that had.

Once I've built that and then a wire dipole I can start the comparison (right now I use a full-wave 160m horizontal loop for all my HF work). I really do wish I had a nice antenna range to do some really objective measurements.

FWIW, here's a URL for the original Petlowany article in World Radio from March 1998: http://www.wr6wr.com/newSite/articles/features/olderfeatures/antennaswithtwist.html
Interestingly, he makes a lot more modest claims than the Tak-tenna site. It's a good read.

73
-Carl AJ4DW

I suppose what we'll be testing is "TAK-tenna... is it really THAT bad?"
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N3OX
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« Reply #32 on: April 09, 2008, 10:31:58 AM »

"Will you be using aluminum or copper wire, and will you try to maintain the smooth spiral"

I dunno, I may try to build one that's as close to the model as possible just to provide a one-to-one comparison, so I'd want to keep the smooth spiral.

I don't want to spend too much time on it, because although I do enjoy the idea of having some good educational information on my website, I don't really want to recommend a difficult to construct structure over an easy coils-and-cap-hats dipole. I'm quite convinced that there's nothing special about the Petlowany/TakTenna construction and that it probably won't outdo good lumped loading.

The problem is that it seems few people will BELIEVE that... not from me, not from W8JI, not from established theory.  Like you, they want to see empirical proof.  A model isn't good enough (and there are are enough subtle modeling pitfalls to make that somewhat valid unless the model has been really tested for convergence).  

But there's always that tradeoff; efficiency vs. useful bandwidth vs. size.  There's no way around it. If you want an efficient radiator, you have to shove current back and forth over some distance.  If you want to shorten that distance and keep the same amount of radiated power, you *have to increase the current*.  If you want to increase the current, you have to *reduce the ohmic losses* in the system to prevent power loss to heat.  If you decrease the ohmic losses so that you can efficiently shove large currents around, while simultaneously decreasing the radiation resistance by shortening the antenna, *you will reduce the bandwidth*

This works to judge small antennas without testing them, by the way.  You see an antenna that's 1/20th of a wavelength in the biggest dimension that covers an entire ham band under 1.5:1 SWR?  It is GUARANTEED to be VERY lossy with respect to a dipole.  GUARANTEED.  It doesn't matter how clever the antenna seems.  The bandwidth vs. radiating efficiency vs. size tradeoff is fundemental for the very best antennas.

However, there's basically no limit to the extent to which you can make things WORSE than the most efficient antenna of a given size and bandwidth. At a given size there are all sorts of things you could do to DECREASE the radiation resistance while keeping the total sum of radiation resistance + loss resistance (and by extension, the SWR bandwidth) the same.

The real question is, for a given size and SWR bandwidth, what is *the most efficient configuration*?  The answer to that question is unknown and likely always will be, but it's at the heart of empirical tests we might want to perform.  It's the question at the heart of good small antenna design.  

Unfortunately, that very same question, UNTESTED, is at the heart of most small antenna marketing campaigns.  The physical form of the antenna is novel, raising that question in the minds of buyers.

The test is carefully avoided by the manufacturer, leaving the buyer to do his or her own tests.  The manufacturer knows that many hams will just stick that sucker up and talk to cool places around the world.

Can I say with 100% certainty based on empirical tests that a Petlowany/TakTenna type loading is worse than conventional coil and capacitance hat loading?  No, not yet, and since so many people clamor for empirical testing, it's probably worth doing some.

But I think I can predict the result.  The finished product based on the design I've set forth will be a narrow bandwidth reasonably efficient short dipole that's not quite as good, but maybe within a dB or two in gain of and has a similar bandwidth to a conventionally loaded coils + cap hats short dipole.  

It's too bad we have to build them to convince anyone of that though, because it's EASIER to build the coils + cap hats version, as far as I'm concerned.  I also have a perfectly good magnetic loop that works 17m in the short/small antennas category and a 17m two element beam... so I don't really need another 17m antenna ;-)

Kinda have to build one now, though, eh?

73,
Dan

 




 



 
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
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« Reply #33 on: April 09, 2008, 10:37:30 AM »

From the article he states that "if a length of wire is wound into a spiral-shaped coil and excited by a radio frequency current connected to the innermost portion of the coil, it will then, and only then, exhibit RF characteristics that closely approximate those of a resonant linear wire of the same length." He seems to be saying that you can take a 1/2 wave dipole and coil it into two spirals and still it is resonant and performs the same as if it were linear. Why is this true of only the spiral form factor?

Regarding the 2M tests that showed it worked as well as a full sized dipole, this 2M dipole ended up being 50% of the full sized dipole. My experience with traditional shortened dipoles is that they work pretty darn well if the physical size is not reduced by more than 50%. I would not expect to see the same performance from his 40M model unless it was similarly scaled, making it at least 34 feet long.

I wonder what the polarization of the other 2M station was. If it was vertical, radiation from the vertical feed line may have made a significant contribution to the signal. The horizontal horizontal test dipole would however take a significant cross polarization hit.

Lots of questions to be answered and very little technical information from either the original article or the Tak-tenna web site. It would be interesting to see some real-world patterns with the feed line adequately decoupled.



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« Reply #34 on: April 09, 2008, 11:25:42 AM »

It sure would be interesting to see what is in the instruction manual that comes with the TAK-tenna wouldn't it?

This antenna is quite interesting from the point of view that it is fun to construct such things. I sure have enjoyed all the posts on this.  73  Bill
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W8JI
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« Reply #35 on: April 09, 2008, 03:57:38 PM »

by AA4PB on April 9, 2008
<<
From the article he states that "if a length of wire is wound into a spiral-shaped coil and excited by a radio frequency current connected to the innermost portion of the coil, it will then, and only then, exhibit RF characteristics that closely approximate those of a resonant linear wire of the same length.">>


Wrong. It is charge acceleration over in-line spatial distance that causes radiation.

1000 feet of wire in a two foot length no matter how coiled, wound, or formed is at very BEST a two foot antenna. It has to have the net or effective common mode current of a two foot long single conductor to radiate the same power.

There is no possible way around this effect.

What this means is if you took the same spatial in-line distance between the end caps and replaced the spiral ends with a metal sheet and added a reasonable lumped inductor in the linear portion of the radiator, you would see a net efficiency increase. This is because the series resistance would decrease.


<< He seems to be saying that you can take a 1/2 wave dipole and coil it into two spirals and still it is resonant and performs the same as if it were linear. Why is this true of only the spiral form factor?>>

It is not true under any condition or any form factor. A five foot linear area antenna is a five foot antenna OR WORSE because radiation is always defined by ampere-feet of linear spatial area.

Linear loaded antenna sometimes use the same false concepts. They claim using more conductor length reduces losses. In fact the opposite is true. That's why there are so many people disappointed by linear loaded 80 meter Yagi's that work poorer than  a simple wire dipole. Some people make big money selling kits that replace linear loading with regular loading coils because the efficiency increases.

The best idea is always minimum series resistance and maximum linear spatial area.

73 Tom  

 
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WD6S
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« Reply #36 on: April 10, 2008, 07:10:31 AM »

On wire length, the instructions that come with the 40M antennas say not to cut off more than 3 feet of wire. Interestingly, depending on how you wind you will have little or a lot of surplus. On one end I tried to maintain a circular pattern and ended up with surplus wire (almost 3 feet). On the other end I "squared the circle" and ended up coming out even.

For the 20 M antenna, the plastic parts are the same size, but the wire is shorter, resulting in many of the inner slots in the cross arms not being used- something that disturbed me enough to send an email. I was assured that this is normal.

The "hot" side, as it is called in the instructions, is fed by the center conductor and is the side closest to boom support clamp.
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K4SAV
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« Reply #37 on: April 10, 2008, 08:10:40 AM »

WD6S, do you have any measurements of the antenna, such as turn spacings, number of turns, or wire length, wire size, etc?  It would be nice to double check my estimated dimensions which were scaled from pictures.  Also there is some question about whether those pictures were even labled correctly.

Jerry, K4SAV
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KE6AEE
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« Reply #38 on: April 11, 2008, 11:35:10 AM »

I personally dont own one or know anybody who does.  Having said that, it sure seems to get good reviews here on eHam. and other places so its not like the builder/company isnt just blowing its own horn.  How good can an antenna be.  Last week I worked Texas from Calif using an Icom 703 at 10 watts with a 23 foot of wire lying on the roof, the other guy running 500 watts into a dipole and he gave me a 54 totally readable and he sent a 46. Just because we might not see electrically/RF wise why it should work.  Lots of crazy designs that shouldnt work but they do.  Thats the thing I love about this hobby.

Richard
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N3OX
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« Reply #39 on: April 12, 2008, 08:16:51 AM »

"Lots of crazy designs that shouldnt work but they do. Thats the thing I love about this hobby"

Richard, that's just the thing.  If you only have one antenna, you're going to love it, because ham radio allows amazing things to happen with tiny radiated power.

Several months ago I worked LA7THA using 5 watts on 160m to an inefficient antenna.   I worked G3ROO on 80m when he was running a chirpy 3W WWII transmitter.  You can probably occasionally work CA <-> TX on much, much less power and much, much less antenna than you were using!  300mW might do it sometimes.

But the fact remains, for each and every path you're interested in working there's an overall total budget for the power and antenna required and if stations on one end  have very small antennas and power, it has to be compensated for at the other.

Keep track over time of how many stations you work that are running 10W to a random wire vs. how many you work that are running 500W to a dipole in the clear or even a beam.  You'll probably find that the number of 10W and random wire stations in your log is generally fairly small.

It's very unlikely I would have ever worked LA7THA with 5W if he hadn't had a much better receiving capability  than I do.  I doubt I would have heard LA7THA if he were running 5W.   I was lucky to hear G3ROO on 80m at 3W.  He was very weak and just at the limit of my receiving capability.  If I hadn't installed the receiving antenna I have, I may not have heard him in the noise.

There's nothing wrong with getting on the air with whatever you've got available for antennas, if you are really limited to those equipment conditions, but don't let the fact that ham radio can do amazing things make you be too complacent about your antenna system.  Maybe it could be *much better* even given your restrictions, and you'd be in here saying "I worked from California to Malyj Vysotskij Island with 10W"

It's fun to work stations using crazy antennas that "shouldn't work" but if you only ever use that one crazy antenna you'll never find out what you've been missing.  There is really no hard lower limit where switching to worse and worse antennas will make you unable to make contacts.  People have literally made contacts using a lightbulb on the end of the coax.

73,
Dan

 
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WD6S
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« Reply #40 on: April 14, 2008, 03:42:07 PM »

Measurements of my Tak Tenna

The end pieces are 30"' long. The 30 inch pieces form a cross. In each arm of the cross there are seven slots cut 1.5 inches apart, starting about .25 inches from the end.

The cross piece is 32 inches long. The coils are separated by 24 inches.

The center conductor terminal is 10 inches from its coil, the hot coil in Tak Tenna parlance.. The braid terminal is 16 inches to its coil, the cold coil in Tak Tenna parlance.

Some notes from the instructions:

Tak Tenna is an electrical half wavelength dipole antenna

If the antennas are not wound in the same direction tuning will be impossible.

If either spiral is cut too short tuning may be a problem.

Rotate Tak Tenna; if you see SWR change it is seeing something.

Antenna feed point changes with elevation.

The Hot spiral affects frequency.
The Cold spiral affects SWR.

It is possible that the antenna will show two minima, one at a lower frequency and one at a higher frequency, both in/around the 40M band. BRING THE LOWER ONE UP FOR RESONANCE.


This information is intended for you antenna analysts to model its performance and I will not give anyone information on the construction details (ie, how the tubing is connected together), as the vendor deserves to maintain his business.

Bob
WD6S
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W8JI
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« Reply #41 on: April 17, 2008, 03:13:33 AM »

It's interesting to hear that two loading coils, both connected in SERIES in a dipole antenna (even at the end), can have different functions.

How can that be?

73 Tom

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IRABREN
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« Reply #42 on: April 17, 2008, 10:43:42 PM »

Well - I have ordered one ( based upon the reviews ) - I haven't tried it yet - but I do respect the e-ham reviews. I am new -  and have built my entire station - based upon the reviews and have not been let down yet! I study the reviews carefully. I don't doubt there may be some fraud in the reviews - The reviews have led me to:
            FT-950 rig
            Ameritron als-600 Amp
            Palstar At1-Kp Tuner
            Force 12 40 XKR antenna
            DX-B alpha delta sloper wire for 160/80m
I am very happy with the equiptment I selected from the reviews. I am so impressed with the e-ham site - I made a contribution.
73, Ira, KE5STP
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N4JTE
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« Reply #43 on: April 19, 2008, 08:42:19 PM »

Trust me, been there did that, it sucks.
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N3OX
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« Reply #44 on: April 21, 2008, 09:34:01 PM »

"I study the reviews carefully. I don't doubt there may be some fraud in the reviews "

Ira, I don't think there's any fraud in the reviews of the TakTenna... just a bunch of people that don't know what they're missing and/or don't understand how the antenna + feedline system works.

They're actually happy with it.  I can't imagine that you would be compared to, say, the Force 12 antenna.

Dan



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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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