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Dumb Questions about Dummy Loads & SWR

from Good Ham's of eHam.net , Thanks! on September 11, 2004
Website: http://www.eham.net/forums/Elmers/70738
View comments about this article!


Dumb Questions about Dummy Loads & SWR Meters

By Martin Brossman - KI4CFS

People said I was a Ham all my life and in fall 2003 I became one. Loving the hobby I wanted to really learn how things work and especially how to test and trouble shoot my own problems. I read in 4 books the importance of an SWR Meter and a Dummy load but the paragraph stopped their. It looked like they cut and pasted the paragraph about these two devices from one book to the next. So I started searching the web for answers on just how do you use SWR Meters & Dummy loads. I found out how you can build them, the problems with low price ones, which models were used to test which equipment but very little on how to really use them. I was clear I was not going to spend $1100.00 on a meter but when I asked which were good ones they referenced the real expensive ones. So I explored the wisdom of Ham's on eham.net in required to using SWR Meters & Dummy loads that were under $200.00 and here is what I learned. I found this very useful and wanted to thank all the ham's that contributed. You will see some redundancy in this article and that is because I am offering different Ham's perspective on the same topic. Sometimes I need to read something in a slightly different way to understand it. May you find these questions and answers helpful to you also!

Question: What is an SWR meter & a Dummy Load AND how do they work?

KA5N: The primary use of an SWR meter is to determine the amount of reflected power in an antenna system. The accuracy of inexpensive meters is relatively unimportant and 10% is good enough. Whether the SWR is 1.1: or 1.3:1 isn't critical. The SWR number accuracy is determined by how closely matched the measurements of the forward reading and the reverse reading are. So in any SWR meter the SWR readings should be pretty close. Where accuracy enters the picture is the forward power indicated. If the meter reads 100 watts is the actual power 90 watts, 100 watts, or 110 watts? For all practical purposes 10% accuracy is good enough. Even the best SWR meters are only about 5%.

A dummy load is used to check the operation of a transmitter and also can be used to check the SWR meter. A good dummy load should show an SWR of about 1.1:1 over its operating range. If your SWR meter suddenly shows an SWR of 5:1 on the dummy load there is a good chance either the meter or the dummy load have gone bad. If your antenna SWR suddenly changes drastically then you check with the dummy load and if that reading is ok something has gone wrong with the antenna system.

Tuning an antenna with a SWR meter is easy with an antenna tuner. You simply tune for lowest SWR (lowest reflected power). Tuning an antenna where you are making an installation means to adjust the length (or coil tap, or capacitor) to give low SWR over the range you intend to operate.

An SWR meter is not a laboratory instrument and for amateur use 10% accuracy is good enough. Using the meter requires a lot of reading of the ARRL Handbook and Antenna Book (and other information sources) and a good deal of hands on use. Learning to diagnose problems in antenna systems from SWR readings requires a good understanding of antenna principles and logical troubleshooting.

K0RFD: How does an SWR meter work? Depends on the meter. There's a pretty good explanation of one type of very simple circuit here:

http://engphys.mcmaster.ca/~elmer101/rfpower/swrtheory.html

How does a dummy load work? It's just a big dumb resistor, non-inductive so that the load is 100% resistive. Essentially, it works by converting nearly all of the transmitter's power to heat instead of radiating it as electromagnetic radiation.

N7DM Another interesting thing about Dummy Loads. Often you will hear or read of someone working across the State or Town...from a Dummy Load, or in one QST article, a Light Bulb. I wouldn't bet YOUR life on it, but I am pretty much sure that the actual radiation was not from the Dummy itself, but from the shield of the COAX feeding it. I have run tests...receive only of course...feeding my old Heathkit Dummy with both coax and twinlead. With twinlead, no length will let me hear a thing. With coax, I CAN hear... and the longer the coax run, the better. So I am pretty sure it goes back to the old Unbalanced Feed to a Balanced Load 'thing'..

Question: How do you use SWR meters with a 10% error, accurately?

K5LXP: Well, if it's specified as 10% accuracy, you'll never have more than a 10% confidence in the reading. However, rarely do you need to know the exact SWR value. Most of the time you're only interested in finding the minimum value (say, when adjusting a tuner), in which case even very inexpensive SWR meters will do this very well.

K0RFD: How do you use a 10% meter accurately? You don't really need to. 10% isn't enough change in reflected power to worry about in most cases. Most meters detect the zero or near-zero reflected power condition pretty well. That's really what you care about. With a cross-needle meter, I generally don't try to read the actual SWR. I just tune for minimum reflected power.

W4TYU: A meter's accuracy is usually expressed as a percentage of full scale reading (5% FS). This means that the error of any reading will be that ammount in error. e.g. If full scale is 100 and the error is 5%FS then the actual error is 5 units at any reading on the meter. If the reading is 50 the actual error would be +/- 5.

Also,remember that that there is a difference between accuracy and precision. A reading can be precise but not accurate.

Question: How do you use an SWR meter to tune an antenna?

K5LXP: In the case of a dipole, you would check the SWR of the antenna under test at fixed intervals (say, 25kHz) across the band it was cut for, and graph the measured SWR vs frequency. The point where SWR is minimum is considered the resonant point. Once this point is known, the length of the antenna can be adjusted to move the resonant point to the desired frequency.

K0RFD: How do you use it to tune an antenna? well, ideally you want to tune the antenna so that the minimum SWR is at or near the part of the band where you operate. Measure the SWR at several frequencies within the band. If you want to move the minimum SWR higher in frequency, make the antenna a bit shorter. If you want to move it down in frequency, make the antenna a little longer. This assumes that the minimum SWR occurs in a range where you are allowed to transmit. Often when you build a new antenna, it's pretty out of whack and the resonant frequency will be outside the range where you are allowed to transmit. (DO NOT TRANSMIT OUT OF BAND) In that case, you measure the SWR at each end of the band. If the SWR is lowest at the lowest frequency of the band, chances are your antenna is too long, make the antenna a bit shorter and see if the minimum swr is within the band. If the lowest SWR is at the high frequency end of the band, then make the antenna a bit longer, again hoping you can get the true minimum inside the range where you can transmit. This is just a rule-of-thumb -- sometimes you can't really tell. In that case, borrow an Antenna Analyzer or Receiver Noise Bridge from somebody and find where the resonant frequency REALLY is.

Question: What is a dummy load used for?

K0RFD: Well the "classic" use was to tune the tank circuit of a transmitter or amp with tube finals without going on the air and QRMing everybody. But a dummy load is useful whenever you want to test or adjust something into a known impedance without going on the air.

Question: How do you use the SWR Meter with a dummy load?

K5LXP: Using an SWR meter with a dummy load is a good way to test cables. Obviously, a dummy load will always present a 1:1 match so you won't be testing it's SWR. But if you *do* measure a mismatch while using a dummy load, the cable or connectors are suspect.

N8UZE: Dummy loads can be used for several purposes. One of these is to tune the old tube type radios so that their output impedance is 50 ohms. On the moder non-tube radios, this is not needed. Another use of the dummy load that does apply to modern radios is adjusting the mike gain. Instead of doing this on the air, you can do it transmitting into the dummy load.

Question: How do you use the SWR Meter / Dummy Load, to determine if your feed line is good or bad?

K5LXP: Using a short patch cable, transmit into the dummy load and set the forward reading for full scale. Insert the cable under test and see that the needle still deflects the needle to almost full scale. If it's significantly lower, there's a problem. If there's any reflected power at all, there's definitely a problem. If the SWR meter has a wattage scale on the forward reading, you can see just how much attenuation the cable has at the frequency you're testing at.

K0RFD: How do you use it to determine if the feedline is good or bad? Connect the dummy load directly to the meter and measure the SWR. It should (ideally) be 1:1 or close. Then connect the feedline to the meter and connect the dummy load to the other end. If the SWR is very high, then chances are the feedline, one of the connectors, or (most commonly) one of the solder joints in the connector is bad. Basically, you are just taking the antenna out of the equation and measuring the SWR of a known impedance with and without the feedline in the system.

Question: How can you determine if the SWR meter is accurate "enough"?

K5LXP: You can connect some known mismatches to the antenna port and see what the readings are. Of course, a 50 ohm load will read 1:1. A 25 or 100 ohm resitive load will read 2:1, and a 12.5 or 200 ohm resistive load will present a 4:1 SWR. No load at all, or a direct short should read infinity to one. Usually, especially with inexpensive meters, the accuracy goes down as the SWR goes up. Pretty much any meter will tell you 1:1, beyond about 5 or 6 to one is tough to accurately measure with a simple instrument.

K0RFD: How can you tell if a meter is accurate "enough" without expensive test equipment? Depends on what you mean by "enough". I really don't pay much attention to absolute SWR values so long as my antenna is close enough to avoid going into power foldback, which most solid-state transceivers do at pretty low SWRs. I just use my meter to find the SWR minimum when I am tuning a new antenna, and to see if anything has changed drastically from last time. The absolute accuracy isn't important, and the precision is usually good enough to tell me if my antenna fell down or the coax came unhooked in the last windstorm.

Question: How can you determine if the 20W range is accurate compared to the 200W range?

K5LXP: Simply sending the same forward power into a dummy load should result in the same readings between the scales, albiet with a bit less resolution on the higher scale. For instance you could set your transmitter for a full scale 20W forward power, then switch to the 200W range. It should still read 20W. The actual power may or may not be exactly 20 watts depending on the accuracy of the meter's calibration. Verifying the actual accuracy is going to require some known standards and an accurate means of measuring voltage or current, or a known calibrated wattmeter?

Question: How do SWR meters tend to go bad, how would you know it, if it did?

K5LXP: A second one is handy to have to compare readings against and is inexpensive. The dummy load and known mismatch standards are a good means of finding a bad meter. The way most VSWR meters work it's not often they suddenly give inaccurate readings. If anything, they will fail completely in one direction or the other due to bad diodes.

K0RFD: SWR meters can go bad in a lot of ways. If it's a D'Arsonval meter, the movement can go bad. You can put too much power into it and burn it out. Connectors can go bad, solder joints can go bad, just about the same things that can go bad with any other piece of electronics. How do you tell? Well, if you can't get a reading on the "calibrate" setting, or if nothing moves under any circumstances, or if you get readings that make no sense at all, test with a dummy load, or borrow a known good meter from somebody else and compare.

Question: How do you use and SWR Meter, what are the different ways?

K5LXP: The most common application is to indicate a good match between a transmitter and feedline. Testing coax is probably the second most. If I need to know any more about a tuned network, antenna, or matching section I'll usually resort to my MFJ-259 analyzer that will tell me inductance, capacitance and a few other parameters that SWR meters cannot indicate. Perhaps some of the real older timers here can pass on some measurement tricks that can be done with basic VSWR meters. One that I know if is how to use an inexpensive 'CB' SWR meter on VHF. One connects it in the usual fashion between the transmitter and the load, and you set the meter full scale per usual. But instead of throwing the switch to reflected to get the SWR, you disconnect the cables on the meter and reverse the connections, and now the forward reading becomes the reflected reading. What this does is use the same diode for both forward and reflected, eliminating the error incurred by the second reflected power diode, which for an inexpensive meter won't be a well-matched pair.

Question: What is the relationship between SWR and Field Strength (radiating energy)?

N7DM: There is no direct relationship between SWR and Field Strength. Field strength basically is a direct function of the amount of current flowing in an antenna. WHERE that field is 'encouraged' to go is dependant on other things...height, ground conductivity, obstructions, other driven elements or parastic elements...etc.

SWR is simply 'ONE' way of numerically stating how well 'something' is matched to something else. There is an SWR on your feedline, IF your antenna feedpoint impedance is not EXACTLY the characteristic impedance of your feedline. There is another SWR on the tiny little piece of coax in your rig that goes from the output filter to the Antenna Output connector, IF the input to your feedline is not EXACTLY what your rig's output impedance is...50 ohms? The only way either of these SWR's can effect your 'Field Strength' is if either one of them permits losses so that some of your output power [causing current in the antenna to flow]...is lost before it gets to the antenna.

KI4CFS: SWR does NOT tell you how much radiating energy is coming from your antenna.
SWR is relevant only when transmitting
, for the most part. It represents the amount of power coming back into the radio. You of course do not want a lot coming into the radio for you do not have an efficient transfer of energy AND you may be putting a strain on the 'finals' (components in the radio) of your radio, also may increase RF in the Ham Shack. BUT low SWR does not mean you are transmitting a strong signal. For example a Dummy Load almost transmits nothing for it is converting all the electrical energy into heat showing a 1:1 or Low SWR. Without something that is testing the actual radiating energy from the antenna and how it changes with changes in SWR you are not getting a total picture.

Question: What is the difference between the Peak Envelope Power (PNP) and Average Power?

N8UZE: The study guide "Now You're Talking" has a fairly thorough explanation. When you were originally studying, there was so much to learn that this probably didn't sink in. Go back and reread it now. However basically as you talk into a microphone on sideband, the amount of power output will vary as you talk. Most meters will give you an Average Power reading. The reading on this type of meter will be and should be less than the max capability of your radio. If it reads full power then you are overdriving the radio and splattering all over the band. If you have a meter that reads Peak Envelope Power instead, it will jump up to max at the points where your voice is max. On FM, AM, and CW both types of meters will give the same reading as it will read the carrier for these modes.

Question: Are their other test tools worth having or having access to (barrowing)?

KI4CFS: From ham's I talked to on the radio the other test tools that seem worth having are a volt-ohm meter, an antenna analyzer, a field strength meter, and a frequency counter. An antenna analyzer hooks directly to the antenna and lets you know information about your antenna with out having to use or endanger your radio. The field strength meter lets you know that RF is radiating out of your antenna and the relative strength of it. The frequency counter tells you the frequency that is dominate in its environment (which would be YOUR antenna if it was radiating well). Last the volt-ohm meter is used to measure AC & DC voltage and DC resistance.

I want to thank all the good natured ham's that have contributed to this resource. My intention is that others find this useful as well. This is a wonderful hobby where both mentoring and community support are richly alive! I truly feel more knowledgeable with my SWR meter from the comments I received and have used them more.

Author: Martin Brossman, KI4CFS is a TRUE Ham in many ways and as a profession is a Executive & Life Coach ( www.CoachingSupport.com ) . He can be reached at: KI4CFS@toinquire.com , (919) 847-4757 and his Ham resource page is: www.toinquire.com/ham

1

Member Comments:
This article has expired. No more comments may be added.
 
Dumb Questions about Dummy Loads & SWR  
by KI4DCR on August 17, 2004 Mail this to a friend!
You go Brossman!!!! Nice work! As a new ham, I learned a lot from this article!

73's dude
Charles KI4DCR
Charles@JaneDever.com
 
RE: Dumb Questions about Dummy Loads & SWR  
by KB9YZL on September 11, 2004 Mail this to a friend!
A great article! More stuff like this is needed!

Thanks!
 
Dumb Questions about Dummy Loads & SWR  
by BILDER on September 11, 2004 Mail this to a friend!
Nice article! Cleared up some questions for sure.

Glad to know that I am not the only one who was having a tough time understanding this stuff.

Thanks to all the elmers out there for the explinations.
 
Dumb Questions about Dummy Loads & SWR  
by KB9YZL on September 11, 2004 Mail this to a friend!
OK....I've got a related question:

I want to buy an antenna analyzer, which will be primarily used for VHF/UHF setups.

What's a good one to buy?.......I don't want to waste money by being "Penny wise and Dollar foolish"!

Kent Carroll
KB9YZL
"Appliance Operator"
 
Dumb Questions about Dummy Loads & SWR  
by WIRELESS on September 11, 2004 Mail this to a friend!
Anyone that reads this article should ask the question why do new or old hams need to know and understand swr? Reflected power, standing waves, forward power, blah, blah, blah. None of this really contributes to practical knowledge thats useful.

If someone took an swr meter, erased all the printing on the box, labeled the reflected power position as "meter position number 1" and then told a new ham to adjust your tuner or antenna until the meter goes to zero or as close as you can get it, we might keep more of the new hams instead of making them suffer though understanding swr so they can make sense out of the meter markings. They can learn it later if they want. Electromagnetic theory doesn't exactly attract people to any hobby including this one.
 
RE: Dumb Questions about Dummy Loads & SWR  
by K1CJS on September 11, 2004 Mail this to a friend!
"Anyone that reads this article should ask the question why do new or old hams need to know and understand swr? Reflected power, standing waves, forward power, blah, blah, blah. None of this really contributes to practical knowledge thats useful."

Wireless, you just refuse to get it, don't you. THIS HOBBY IS A TECHNICAL HOBBY AND NEEDS TO BE RECOGNIZED AS A TECHNICAL HOBBY. Ham radio licensees are allowed by law to build, adjust and test their own radios and radio systems. There is no other radio service that where the individual operators are permitted to do that.

That one fact alone makes it important to have that technical know-how. Just as morse code is still important and looked upon as necessary for access to the lower bands for some, technical knowledge and skill is looked on as necessary to far more. Not to mention that knowledge of band limits and the bandwidth needed for various modes is necessary to insure in-band operation by operators.

If you ever get your license, or upgrade it on the slim chance you are licensed, I'd love to hear your comments when you get you warning notice about your illegal operations. You'll wish you knew those technical tidbits then. 73.
 
RE: Dumb Questions about Dummy Loads & SWR  
by WIRELESS on September 11, 2004 Mail this to a friend!
Those that think they got it really don't, they aren't smart enough so maybe they need it explained.

Fact:

#1 Just because someone has a license or interest in this hobby doesn't mean they define it for everyone else. YOU aren't running anything and you are not going to either.

#2 Just because you pull web pages down with your browser, doesn't mean you run this "site" which isn't a place or a site, they are just web pages displayed on your monitor.

#3 Old fart hams will not be allowed to dictate to other hams or anyone else because as much as you would like to think you are important and have clout, you got nothing.

#4 As much as you may think you can play "gang up on 'em" games, I hate to tell you that they don't work with a keyboard on an internet site.

#5 No one on this "site" is going to be intimidated to conform to those that think they are the majority. Again, you are irrelevent.

#6 When nothing else works you may continue running to the site managers to whine and moan to get them to censor those you don't like. I don't think anyone cares if they are banished from this crowd.

#7 .....I have wasted enough time!
 
VHF/UHF analyzers  
by KZ1X on September 11, 2004 Mail this to a friend!
Kent

There are few good choices for VHF/UHF analyzers. The one I found best is the Autek, which covers all the way up to 500+ MHz. VERY accurate. I popped one of the microwave-grade diodes, but was able to find what I did (with help from the very helpful Autek owner and designer!) and voila, it's back on-line.

KZ1X
 
RE: Dumb Questions about Dummy Loads & SWR  
by KB9YZL on September 11, 2004 Mail this to a friend!
WIRELESS;

Maybe I'm stupid, senile, or clueless.....All I know for sure is that I don't have a clue as to what point you're trying to make!!

How about if you "throttle back" on the insults, and restate your position???

Kent Carroll
KB9YZL
"Appliance Operator"
 
RE: VHF/UHF analyzers  
by KB9YZL on September 11, 2004 Mail this to a friend!
KZ1X;

Thanks........I'll read up on the Autek unit.
 
Do Cantenna Type Dummy Loads - Radiate ?  
by WB9YCJ on September 12, 2004 Mail this to a friend!
I live in southern California. While using a Cantenna, I once had a QSO with a fellow in northen california on 40M. He gave me a signal report of S-7. I did NOT have a hot microphone (station wasnt grounded). So how did this happen? I have been told Cantennas do INDEED radiate. Ken
 
RE: Do Cantenna Type Dummy Loads - Radiate ?  
by KA4KOE on September 12, 2004 Mail this to a friend!
"#7 .....I have wasted enough time!"

Great..Let the kiddies have fun in this play room!
 
RE: Dumb Questions about Dummy Loads & SWR  
by KI4CFS on September 12, 2004 Mail this to a friend!
You asked about a UHF / VHF Analyzer, well MFJ makes one, but I like the:

AUTEK RESEARCH RF5 VHF Analyst
( 35 - 75 & 138 - 500+ MHz )SWR True Impedance (Z)
Automatically Finds Minimum SWR or Z

You can see it at:
http://www.autekresearch.com/

Fits in the palm of your hand, better, written manual than the MFJ, uses a 9 Volt battery.

The other would be the MFJ model.
KI4CFS

 
RE: Dumb Questions about Dummy Loads & SWR  
by K1CJS on September 12, 2004 Mail this to a friend!
Oh! OK there Wireless, I get it now.......

No one can dictate what ham radio should be EXCEPT YOU--right? It certainly seems so, because that's what you are most certainly doing.

In any case, I wasn't trying to dictate, all I did is try to state in terms everyone could understand why some things are required, including morse code.

I certainly am sorry I riled you--NOT!
 
RE: Dumb Questions about Dummy Loads & SWR  
by KI4CFS on September 12, 2004 Mail this to a friend!
At topic that I want to explore next is the use of power meters and Antenna Analyzers...Maybe someone else can do that!

Thanks for the ackoledgements and comments. This is my first article for eHam.net, a great site and resource for me.

Thanks: Martin Brossman
KI4CFS@toinquire.com
Ham Radio Resources
http://www.toinquire.com/ham
 
RE: Dumb Questions about Dummy Loads & SWR  
by N2LJD on September 13, 2004 Mail this to a friend!
KI4CFS - "At topic that I want to explore next is the use of power meters and Antenna Analyzers...Maybe someone else can do that!" Hope not! I look forward to your next compilation!

Thanx for the great article. Refreshed my memory at a very appropriate time as my mobile installation (ICOM IC706MkIIG, AT-180, Comet UHV-6) is giving me conniptions with SWR and I've been troubleshooting with no luck (have my MFJ-269B with me). I'm away from home so I've ordered a dummy load to be delivered to my hotel so I can continue troubleshooting, and your article has given me some ideas to try.

73 OM FB!

Joe
 
RE: VHF/UHF analyzers  
by KI6LO on September 13, 2004 Mail this to a friend!
Not to add fuel to the already growing 'flames' but I would suggest that a perspective analyzer purchaser visit the product review sections here on eham.net and qrz.com as well as other websites (do a web search to find them).

I am current looking at several different brands of analyzers myself. Each has pros and cons. Not to belittle any brand, I was suprised at the comments made of some of the so called 'professional' models. I really like to try out gear if at all possible and have used a MFJ-259 HF/VHF analyzer quite extensively (no I did not buy it but rather borrowed it to test). I had originally considered an Autek but after reading some of the reviews I want to actually put my hands on one and test it before going simply on the mfgrs claims.

I suggest that you do your 'homework' and don't rely on only the mfgrs claims and specs to make you decisions. Since the ads are designed to make each brand sound a bit better that the others, it is only common sense to figure that the information is 'polished' as much as legally possible to make the gear sound foolproof. My experience says otherwise.

73

Gene KI6LO
 
Dumb Questions about Dummy Loads & SWR  
by KI6LO on September 13, 2004 Mail this to a friend!
A Bird Model 43 wattmeter (or equivalent) is another device that is very useful after owning one for a couple of years, I wonder how I ever got along without it.

They can be found on eBay and such for a very modest investment ($200 - 300) condsidering the usefulness. They are very solidly built and by using inexpensive interchangeable frequency elements (like having another high quality wattmeter for $50), they can cover HF, VHF, UHF from QRP to tens of kilowatts, with UHF or N style connections. They read forward and reverse power very accurately. WITHOUT having to calibrate any meters or knobs - only by rotating the element 180 degrees in the socket and using a very simple nomograph (chart) to compare FWD to REF power levels, the SWR can also be calculated.

Just some more ideas,

Gene KI6LO
 
RE: Dumb Questions about Dummy Loads & SWR  
by W2ELV on September 14, 2004 Mail this to a friend!
Great article for someone like me who's going on to a General ticket. I've been an electronics hobbyist over 45 years, but only recently did I get interested in Ham radio. This article goes a long way to help me understand how to tune an antenna.
 
Dumb Questions about Dummy Loads & SWR  
by WA2JJH on September 15, 2004 Mail this to a friend!
As a 16 year old novice, I used a 100W bulb as a dummy load. It was not half bad either. I do not recommend it.

I got a 2:1 SWR out of the bulb. This does not make sense. Perhaps the inductive reactance of the bulb fooled the SWR meter.

For QRP, a #46 light bulb was recommended by many.
If it light, you knew you had at least 1 W out.
If you blew the bulb >4W!

I do find dummy loads today, under-rated. The dummy load in the el cheapo MFJ meters are WIRE-WOUND resistors! They will handle 300W for 10 seconds BTW!
Then the resistor turns into a toaster!

I find the DRY loads are not so hot for long tune ups. I had a IKW job. It fried with 600W CW after 30
seconds.

Another thing I noticed. An SWR meter may read 3:1 at the shack. However at the antenna feed point 10:1!

 
Dumb Questions about Dummy Loads & SWR  
by WA6BFH on September 16, 2004 Mail this to a friend!
Martin, As many others have told you, I too appreciated your article, and from those who provided answers -- I learned a lot!

I was amazed at the skill of a few to give quite accurate answers in relatively few words. I was alarmed at some of the answers, and terrified by some others!

Let me give this a whack!I think I would answer the prospective "Elmeree" thusly. Well, you should consider this.

1) The real value in buying and owning a high quality VSWR meter (actually I would suggest a "Directional Wattmeter") and equal quality "Dummy Load" is this. It will save you a lot of expense, trouble, and worry as you build your station, antennas, and select various feed-lines.

2) The first thing that you must appreciate to use such devices is that, ALL RF DEVICES such as antennas ARE REACTIVE TUNED CIRCUITS -- THEY HAVE REACTANCE! Uh, except for a high quality Dummy Load! It should represent a "purely resistive load" up to the highest frequency for which it is rated. So, get a good one that works all the way up into the microwave spectrum -it will also work just dandy all the way down to 160 Meters! Also, buy a book titled, "Reflections" by Walter Maxwell. It will teach you all the things that I can't answer here in a few words!

3) Keep in mind that the meter itself can inject "Reactance" into the "Antenna System" if it is not well designed. An example would be an SWR Bridge wherein the "Directional Coupler" of that bridge is about 6 inches long, and you want to take measurements on the 70 centimeter wavelength band. Afterall, 6 inches is about a quarter wavelength at that frequency, and we of course know that every quarter-wavelength impedances invert! Even at 2 Meters a 6 inch coupler would become something of a 'transformer' or "impedance bump".

4) So, in summary, go ye fourth and buy a very high quality Directinal Wattmeter, and equal quality Dummy Load that will handle at least a good solid 100 Watts.
These devices, even though perhaps expensive, will save you money, hassle, and enhance your enjoyment of what you learn with them for many many years to come!
 
Dumb Questions about Dummy Loads & SWR  
by KI4ENY on September 17, 2004 Mail this to a friend!
I just became a ham a few monthes ago, and I knew nothing about how to use a SWR meter and a dummy load. Thank you for an excellent article with lots of information. I really learned a lot.

73,
Chris, KI4ENY
 
RE: Dumb Questions about Dummy Loads & SWR  
by VU2WE on September 18, 2004 Mail this to a friend!
Ok WIRELESS just read your comments-
"Anyone that reads this article should ask the question why do new or old hams need to know and understand swr? Reflected power, standing waves, forward power, blah, blah, blah. None of this really contributes to practical knowledge thats useful."

I am having a hard time understanding your statement. If this is a technical hobby and there is some degree of technical expertise involved in operating and maintaining the signal that you are transmitting, and you are legaally responsible for the transmission of that signal, why do you insist on not understanding what the components are and how they function in your antenna system?

Why wouldn't you want to know what forward power is, why wouldn't you want to know what reflected power is? Why wouldn't you want to know about the instrumentation necessary to adequately measure those parameters? I don't understand? This is not advanced calculus that one is trying to learn. It's the Principles of RF Antenna Systems 101. It doesn't get any simpler than this.

What, may I ask, is your solution? Wait, don't answer that yet, I bet it's "buy my radio at the radio store- buy me a dipole antenna kit with them there connectors already put on by the peoples at the factory-buy me a microphone- plug it into the box that the instructions say I gotta plug into-plug in the connector-and then press the button and talk" Yeah right, and when you finally realize that you're not radiating any RF (sorry for the technical term there)out of your antenna and haven't a clue why, then maybe it's time to open a book (terrible thing to do) and learn something.

Do us and everyone else a favor, keep your simpleton comments to yourself and your "instant gratification" buddies. You do nothing constructive for the hobby. You're always crying about having to learn something.

And oh, by the way, we are Old Timers, and we not only design web pages and web sites, we design the software that allows ALL PEOPLE to use web authoring tools.

So don't give me this Internet crap that you think you're only privvy to.

We are ALL tired of hearing your POV. Keep it to yourself. Just who do you think you are with your pompous bullying tone?. You don't intimidate me.
Go home, get a job and get a life dude.


Namoste- Klaus
 
RE: Dumb Questions about Dummy Loads & SWR  
by KI4CFS on August 30, 2005 Mail this to a friend!
Thanks for all the great comments about my 1st eham article!

Take care,
Martin KI4CFS

I have also build a web page for resources for all ham's .

http://www.toinquire.com/ham

Thanks!
 
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