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[Articles Home]  [Add Article]  

A Tuner's Effect At The Antenna

Cecil A. Moore (W5DXP) on March 26, 2013
View comments about this article!


Old Wives' Tales In Amateur Radio

Chapter I: "An Antenna Tuner Does Absolutely Nothing Except Make The Transmitter Happy."

by Cecil Moore, www.W5DXP.com, Rev. 1.0, March 3, 2013

Wikipedia's Take on Old Wives' Tales

Introduction

Judging from the number of Old Wives' Tales that abound in amateur radio, there must be more old wives in amateur radio than can be found in The Call Book. The author hears this one at least twice a week on some ham radio newsgroup. This article is an attempt to debunk that myth using the most simple of examples hopefully that everyone can understand. This will be the first in a series of "Old Wives' Tales" articles that will be compiled into chapters on the author's web page.

Let's not quibble over whether a transmitter is capable of human-like feelings or not. What is meant by "making the transmitter happy" is the concept that an antenna tuner presents a resistive load of 50 ohms to a transmitter designed to drive a 50 ohm load, usually of the solid-state variety. The author conceeds the idea that an antenna tuner "makes the transmitter happy". The question remains: Is "making the transmitter happy" all that an antenna tuner does or does the antenna tuner also have an effect at the antenna, i.e. does that 50 ohm Z0-match that "makes the transmitter happy" also have a system-wide effect that makes the entire system, including the antenna, happy? If a transmitter can be happy, why can't an antenna be happy?

We are going to look at some simple examples. The source will be a voltage source, (VS), with an associated source impedance of the complex form (RS jXS). Any transmission line will be one wavelength long and lossless (1WL T-Line). The load will represent an antenna feedpoint impedance of the complex form (RL jXL). We will represent such systems using one-line diagrams of the form:

(VS)--(RS jXS)----------(RL jXL)

The Maximum Power Transfer Theorem

The maximum power transfer theorem was first used with DC circuits. Given a source and a load, the theorem says that: Maximum power transfer will occur if the source resistance is equal to the load resistance. This is probably the origin of the myth that, for maximum power transfer to occur, an antenna must present a purely resistive, e.g. 50 ohm impedance, i.e. must be resonant.

When AC circuit theory was developed, it was apparent that the resulting reactive impedances would require the DC maximum power transfer theorem to be updated. That's when the conjugate matching theorem came into existence. Given an AC circuit: Maximum power transfer will occur if the source impedance is equal to the conjugate of the load impedance. Note that the conjugate of 100+j100 ohms is 100-j100 ohms and the conjugate of 50-j200 ohms is 50+j200 ohms. Both the above theorems apply to lumped-circuits.

When networks that are an appreciable percentage of a wavelength were introduced, it again became apparent that the maximum power transfer theorem needed to be updated since a transmission line with reflections is capable of transforming the complex load impedance to an infinite number of other complex impedances and also to some purely resistive impedances. Let's take a look at how the maximum power transfer theorem can be updated to handle distributed networks. We can do that by looking at one characteristic of the maximum power transfer theorem for an AC circuit represented by the one-line diagram introduced above with point 'x' added.

(VS)--(RS jXS)-----x-----(RL jXL)

The voltage source, (VS), just by itself is defined as having a zero impedance. So if we measure the impedance looking back from point 'x' toward the source, we will measure the source impedance, (RS jXS). If we measure the load impedance looking toward the load from point 'x', we will measure the load impedance, (RL jXL). So another way of stating the maximum power transfer theorem for an AC circuit is: From a point between the source and the load, if the impedance looking back toward the source is equal to the conjugate of the impedance looking toward the load, then maximum transfer of power will occur. That is also the definition of a "conjugate match".

When the maximum power transfer theorem is applied to a lumped-circuit, it is assumed that the only losses in the circuit are losses in the source resistance and the load resistance. If we adopt that same assumption for distributed networks, we can now take the liberty to state the maximum power transfer theorem for a typical amateur radio antenna system (assuming lossless transmission lines.)

(VS)--(RS jXS)-----Transmission-Line-----(RL jXL)

A maximum transfer of power will occur in an antenna system when, at any point on the lossless transmission line, the impedance looking back toward the source is equal to the conjugate of the impedance looking toward the load.

Once again, the above statement can be considered as a necessary and sufficient condition to define a conjugate match.

Numbered Step-By-Step Examples

For the remainder of this article, we will assume that VS=100v, RS=50 ohms, and XS=0 ohms, i.e. a standard voltage source and RL=50 ohms. Also remember that all transmission lines are lossless.

(1)Source(100v)--(50 ohms)---------1WL T-Line------------(50 ohms)Load

So here we have a matched system with 50 watts delivered to the load which is the maximum transfer of power. What happens to the power delivered to the load if we mismatch the system by adding -j500 ohms of capacitive reactance to the load?

(2)Source(100v)--(50 ohms)---------1WL T-Line------------(50-j500 ohms)Load

Only 1.92 watts are delivered to the load for example (2). The current through the load resistor is 0.196a and the voltage across the load resistor is 9.8 volts. What can we do to change those conditions at the load? How about adding a loading coil with a reactance of +j500 ohms?

(3)Source(100v)--(50 ohms)---------1WL T-Line------------(+j500 ohms)--(50-j500 ohms)Load

So the loading coil reactance of +j500 ohms neutralizes the load reactance of -j500 ohms and, once again, as in (1) above the maximum power of 50 watts is delivered to the load.

Question: Did the addition of a loading coil have an effect at the load (antenna)?

What if, instead of at the load, we install the loading coil at the source?

(4)Source(100v)--(50 ohms)--(+j500 ohms)---------1WL T-Line------------(50-j500 ohms)Load

Question: Does the loading coil installed at the source cause the same effects at the load (antenna) as it did when it was located at the load (antenna), i.e. do the same conditions exist at the load in example (4) as in example (3)?

What if we put the "loading coil" in a box at the source and call it an "antenna tuner"?

Question: Does an antenna tuner have considerable effect at the antenna or does it "do absolutely nothing except make the transmitter happy"?

It seems to the author that since the "antenna tuner" has the same effect on the load whether it is located at the load or at the source, an Old Wives' Tale has bit the dust. It stands to reason that if an antenna tuner causes the antenna to radiate more RF power then it is obviously having considerable effect at the antenna from whence that RF power is being radiated. In fact, the list of things that are changed at the antenna by the antenna tuner is just about as long as the list of things that are not changed.

Note that, no matter where the loading coil is located above, it has the same effect of establishing a system-wide conjugate match thus ensuring maximum power transfer. If we measure the impedance looking back down the transmission line from the load, we will measure the conjugate of the feedpoint impedance in both examples (3) and (4) above. The effect on the antenna (load) is the same whether the loading coil is located at the antenna or at the source (shack).

One can see for oneself the effect that an antenna tuner has at the antenna. Install a dummy load on the tuner input and at the antenna feedpoint, disconnect the feedline and connect it an antenna analyzer. Have someone twist the knobs on the tuner and observe the impedance change at the antenna. Then who can truthfully say that an antenna tuner has no effect at the antenna?

For the sake of simplicity, transmission line losses, which make the calculations much more complex, have not been taken into account. Failure to include losses does not negate the concepts presented in this article. Note that the conjugate matching theorem applies only to lossless networks and just comes close for low-loss networks.

Member Comments:
This article has expired. No more comments may be added.
 
A Tuner's Effect At The Antenna  
by KA4KOE on March 26, 2013 Mail this to a friend!
A good sequel to this article would be a discussion of the honored and venerable Smith Chart.

Good work!

Philip KA4KOE
 
A Tuner's Effect At The Antenna  
by NV2A on March 26, 2013 Mail this to a friend!
Well, ah, lemme see, were we to, no wait. If a station in Buffalo, NY radiates two signals one through an auto tuner located at base of antenna and then sends the same signal with a tuner located at the xcvr location, will the signal level received be the same in Houston Texas for both of these signals?

Not being as adept with antenna theory as I'd like to be it's hard for me to make much sense of the article. Were I able to make sense of it, I would be adept enough at the theory that the article would not add anything new for me.

I think your conclusion could be a little simpler to understand for those of us in need. It's pretty obvious that you know your stuff. Thanks for taking the time to put this all together. 73's
 
RE: A Tuner's Effect At The Antenna  
by AA4PB on March 26, 2013 Mail this to a friend!
While this article does not address transmission line losses, those losses are indeed a key part of most any antenna installation. Those losses are what the "old wives tale" is intended to address in very simplistic terms. A tuner is not a magic box that can turn any antenna system into an efficient one on any band.

It is important to note that a tuner located at the transmitter does not alter the SWR on the feed line between the tuner and the antenna therefore it does not reduce the loss in that transmission line. If your transmission line has a 10:1 SWR and 10dB of loss then your transmitter will likely not be able to load it and will reduce power output to protect itself. If you add a tuner at the transmitter then it will match the impedance at the end of the feed line to the 50 Ohm transmitter and the transmitter will operate normally. The feed line however still has a 10:1 SWR and 10dB of loss.

 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 26, 2013 Mail this to a friend!
> NV2A wrote: I think your conclusion could be a little simpler to understand for those of us in need. <

How about this? The major difference in locating a tuner at the antenna feedpoint vs in the shack is feedline losses. If the coax feeding the tuner at the antenna feedpoint has the same losses as the ladder-line feeding the antenna directly (with the tuner in the shack) very close to the same conjugate match conditions will exist at the antenna feedpoint in both cases. No matter where the tuner is located in a low-loss system, it has essentially the same effect at the antenna feedpoint.
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 26, 2013 Mail this to a friend!
> AA4PB wrote: The feed line however still has a 10:1 SWR and 10dB of loss. <

I hope I made it clear that I was writing about low-loss systems in which transmission line losses are negligible. 10dB of loss in a transmission line is obviously not a low-loss system. However, if the 10:1 SWR on the open-wire transmission line results in 0.2dB of loss, we can usually consider that figure to be negligible.

But please note that at an SWR of 10:1, even if the losses in the transmission line are 10dB, a tuner in the shack will still have a measurable effect *at the antenna feedpoint*, just not as large an effect as in a low-loss system.
--
73, Cecil, w5dxp.com
 
A Tuner's Effect At The Antenna  
by KI5FJ on March 26, 2013 Mail this to a friend!
Great article! Since todays real world consists of mainly coaxial 50 Ohm transmission lines the Z match at the antenna is the most efficient.
I use a combination of Open-Line and 7/8 inch Heliax
for my Loops and Vertical. In my real world I also use a ATR-30 in the shack. Thanks for the topic.
73 Joe O, NNNN
 
RE: A Tuner's Effect At The Antenna  
by N4KC on March 26, 2013 Mail this to a friend!
Yep, good article, Cecil. It all finally came clear to me when I accepted the notion that everything from the final output stage of the transmitter on was part of an ANTENNA SYSTEM. Anything in that SYSTEM has an effect on everything else within the SYSTEM. Some things you can control, some you can't...unless you pack up and move to another location!

73,

Don N4KC
www.n4kc.com
www.donkeith.com
(Author of the new book RIDING THE SHORTWAVES:
EXPLORING THE MAGIC OF AMATEUR RADIO)
 
A Tuner's Effect At The Antenna  
by AB9TA on March 26, 2013 Mail this to a friend!
I really enjoy it when the Old Wives take a loss..

One other wives tale to take on regards transmission line losses in mismatched antenna systems at HF, i.e., it always causes very high losses.

VSWR can cause additional losses in an HF system, but they are negligible for commonly used coax and antennas that are appropriate for the band in use.
If you calculate the actual losses, (I like the VK1OD calculator, but there are others. http://vk1od.net/calc/tl/tllcr.php ), you can determine if they are acceptable to you.

For example, I use a 160M OCF dipole fed with 100' of RG6A/U coax to a 1:1 current balun for all bands 10-160. I'll assume that on some bands I could have a 10:1 SWR because feedpoint impedance varies by frequency on this antenna. (However, it isn't as wide a swing as with center-fed antennas. Usually the mismatch is much lower).

Assuming the 10:1 mismatch is on:

10M, my transmission line loss goes from 0.85db (matched) to 2.9db (mismatched), an increase of a little over 2db. Pretty much negligible, although it's right on the borderline of being a concern. As I go lower in frequency, it gets better.

20M, the losses go from 0.58db to 2.2db, a 1.6db change. Negligible to me.

80M, the losses change from 0.3db to 1.3db, a 1db change - Negligible.

160M, it ends up as a 0.74 db change from matched to mismatched.

Why do I use 75ohm Sat TV coax? It's low loss, cheap and easily available. And as you can see, the losses from a mismatch on this coax is not worth worrying about, especially on the lower bands. On the higher bands, this antenna pattern has a lot of peaks and nulls, I have more problems with that than with really minor transmission line losses.

Obviously you can find a combination where the losses could be considered excessive (Very short antennas, 20:1 and higher VSWR, lossy coxes like RG-58, RG-174, etc.) even at HF.
But the point is that a mismatch that is corrected by a tuner at the transmitter is probably not causing huge transmission line losses that we all think of.

Also, if you are running above 100W or so, mismatches can cause some pretty high peak voltages that could cause breakdowns of coax, etc.
But for most hams with modest HF setups, a tuner with decent coax will get the job done..

At some point we all have to make a db to dollars analysis to see how much that loss is worth to you..

And as always, a compromise antenna is far better than no antenna at all!

73!
Bill AB9TA

 
RE: A Tuner's Effect At The Antenna  
by AA4PB on March 26, 2013 Mail this to a friend!
"At some point we all have to make a db to dollars analysis to see how much that loss is worth to you.."

If you do the analysis as you have done and make that determination that's great. The problem is that some don't make the analysis. They assume that the tuner in the shack fixes everything because it makes the radio's SWR meter read 1:1.
 
A Tuner's Effect At The Antenna  
by N7AG on March 26, 2013 Mail this to a friend!
Ah, the truth rears its ugly head! A follow-up using the Smith charts would help me.

Tnx, Bill N7AG
 
RE: A Tuner's Effect At The Antenna  
by N6JSX on March 26, 2013 Mail this to a friend!
Beware - if you go into Smith Charts (like S Curves) you will loose >90% of the article readers! Or generate some really eye opening comments/questions!
 
RE: A Tuner's Effect At The Antenna  
by G3RZP on March 26, 2013 Mail this to a friend!
If you get maximum power transfer when conjugately matched, how can you get more than 50% efficiency when using a Class C PA?

For that matter, why aren't power stations conjugately matched but attempt the lowest possible source impedance?

The explanation from the transmitter engineers at Marconi was that ideally, the tx was 0+j0 source when feeding the designed load.....

Which does make sense. But are there other explanations? (other than one offered which was that the tx source impedance was a 'lossless resistance'.
 
A Tuner's Effect At The Antenna  
by M6GOM on March 26, 2013 Mail this to a friend!
"For the sake of simplicity, transmission line losses, which make the calculations much more complex, have not been taken into account."

So the part which is where the most losses occur hasn't been taken into account?

You cannot look at it without taking the feeder losses into account and it is because of those feeder losses that a tuner at the antenna end is far more desirable than one at the source end of the feeder.
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 26, 2013 Mail this to a friend!
> G3RZP wrote: If you get maximum power transfer when conjugately matched, how can you get more than 50% efficiency when using a Class C PA? <

The maximum power transfer theorem applies only to linear systems. A class-C PA is not linear. If we are to use the maximum power transfer theorem, we are stuck with linear (class-A) sources.

> M6GOM wrote: You cannot look at it without taking the feeder losses into account and it is because of those feeder losses that a tuner at the antenna end is far more desirable than one at the source end of the feeder. <

The maximum power transfer theorem assumes lossless transmission lines. Therefore, so did I.

But let's see if your above "far more desirable" statement is always correct. Let's assume the same tuner losses whether the tuner is located at the shack or at the antenna. The frequency is 40m and the antenna feedpoint impedance is 200+j760 ohms.

XMTR--tuner-------100' of open-wire-----antenna

VK1OD's feedline loss calculator says the loss in the open-wire feedline is 0.418 dB.

Now let's put the tuner at the antenna and feed it with 100 feet of RG8x. With an SWR of 1:1, the losses on the RG8x are 0.770 dB, higher than the open-wire line. Even with RG-213, the losses would be 0.454 dB.

Looks like putting the tuner at the antenna feedpoint is not always "far more desirable" and in the above case, the tuner at the shack is performing the maximum available power transfer admirably. In a low-loss system, the tuner performs the same system resonating function no matter where it is located.
 
A Tuner's Effect At The Antenna  
by VE3TMT on March 26, 2013 Mail this to a friend!
?????????
 
RE: A Tuner's Effect At The Antenna  
by K5TED on March 26, 2013 Mail this to a friend!
With a "very short antenna", say, a 40' wire, fed with 100' of RG-213, which is more efficient radiating system?

A. Tuner between radio and coax, 9:1 unun at the wire feedpoint.

B. Tuner or "auto-coupler" outside at the wire feedpoint. Coax connected directly to radio.

Specifically, I'm asking about the practice of using "auto-couplers" at the antenna feedpoint as opposed to a manual or auto tuner at the radio end. (typical in marine applications, feeding a backstay wire, etc.)

 
RE: A Tuner's Effect At The Antenna  
by NN5AA on March 26, 2013 Mail this to a friend!
Cecil,W5DXP, you said, "In a low-loss system, -----the tuner performs the same system resonating function----- no matter where it is located."

So Cecil, you are saying that the tuner is electrically making the system 'resonant', through either additional capacitance or inductance, or a combination thereof? Is being 'resonant' and 'conjugately matched' or 'load matched to source' all one and the same, or different sides of the same coin, or are they entirely different animals??

I am most interested to hear your explanation!




73, Vince -- NN5AA

A 100% fully functioning boat anchor!!




 
A Tuner's Effect At The Antenna  
by VE3XQQ on March 27, 2013 Mail this to a friend!
Excellent work!

This is a very fine article on the tuning of our RF radiating 'system' we call an antenna, reminds me of articles by Jack Belrose.

For those wanting more on swr and transmission lines look at the 2005 article:

"An Energy Analysis at an Impedance Discontinuity in an RF Transmission Line, Part II"
http://www.eham.net/articles/12744

Thank for penning this for us.
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 27, 2013 Mail this to a friend!
> K5TED wrote: With a "very short antenna", say, a 40' wire, fed with 100' of RG-213, which is more efficient radiating system?
> A. Tuner between radio and coax, 9:1 unun at the wire feedpoint.
> B. Tuner or "auto-coupler" outside at the wire feedpoint. Coax connected directly to radio.

I would never choose 'A' for a very short (40') antenna which has a feedpoint impedance on 80m of about 3.8-j1173 ohms and a 9:1 balun would try to bring that down to 0.42-j130 ohms, an almost impossible impedance for a tuner to try to match not to mention a sky high SWR with extreme losses on the coax. 'A' should only be used with long non-resonant dipoles, not short ones.

'B' would be the best choice although the performance will leave something to be desired. For instance, a CB whip driven by an autotuner on 80m will load but is less than 1% efficient.

The best solution is to take (W2DU/SK) Walter Maxwell's advice. Make any dipole at least 3/8 wavelength on the lowest frequency of operation. The G5RV is 3/8WL on 80m.

> VE3XQQ wrote: http://www.eham.net/articles/12744 <

That one is outdated. The three-part article has been condensed, revised, and is on my web page at:

http://www.w5dxp.com/energy.htm
 
RE: A Tuner's Effect At The Antenna  
by M6GOM on March 27, 2013 Mail this to a friend!
"With a "very short antenna", say, a 40' wire, fed with 100' of RG-213, which is more efficient radiating system?

A. Tuner between radio and coax, 9:1 unun at the wire feedpoint.

B. Tuner or "auto-coupler" outside at the wire feedpoint. Coax connected directly to radio.

Specifically, I'm asking about the practice of using "auto-couplers" at the antenna feedpoint as opposed to a manual or auto tuner at the radio end. (typical in marine applications, feeding a backstay wire, etc.) "

Without any doubt option B - it has the least losses. With option A, on most bands much of the power is dissipated as heat within the 9:1 unun in addition to coax losses. The tuner at the shack merely matches a slight mismatch of 3:1 or thereabouts.
 
A Tuner's Effect At The Antenna  
by KB2VEC on March 27, 2013 Mail this to a friend!
This begs the question, that given the same input power would you get the same s meter reading if you used a resonant antenna and same feedline etc. as opposed to a non resonant antenna and tuner in a receiver some distance away from the antenna.

Paul T.Harris
KB2VEC
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 27, 2013 Mail this to a friend!
> NN5AA wrote: So Cecil, you are saying that the tuner is electrically making the system 'resonant', through either additional capacitance or inductance, or a combination thereof? Is being 'resonant' and 'conjugately matched' or 'load matched to source' all one and the same, or different sides of the same coin, or are they entirely different animals?? <

The IEEE definition of "resonance" is the frequency at which the RF signals and fields reach their peak values throughout a frequency sensitive system. That is what a tuner accomplishes. A conjugate match at the feedpoint of a frequency sensitive standing wave antenna implies system-wide resonance and maximum transfer of available power. However, the maximum power transfer theorem and conjugate matching theorem deal only with lossless transmission lines. In the real world, we can only get close to a system-wide conjugate match using low-loss transmission lines. If the transmission line is high-loss, we can't even get close to a system-wide conjugate match and have to be satisfied with a conjugate match at a single point in the system which is often the 50 ohm Z0-match at the tuner input.

If there is no reactance present, an impedance match and a conjugate match are the same thing, e.g. 50+j0 equals 50-j0. But if reactance is present, they are not the same thing and an impedance match will ensure that we do not achieve maximum available power transfer. For instance, a 50+j50 ohm source impedance driving a 50-j50 ohm load will deliver maximum available power to the load while that same source driving a 50+j50 ohm load will NOT deliver maximum available power. Hope this helps.
--
73, Cecil, w5dxp.com

 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 27, 2013 Mail this to a friend!
> KB2VEC wrote: This begs the question, that given the same input power would you get the same s meter reading if you used a resonant antenna and same feedline etc. as opposed to a non resonant antenna and tuner in a receiver some distance away from the antenna. <

Almost a trick question - We can say that a well-designed non-resonant antenna system can radiate the same amount of power as a resonant antenna system, i.e. if properly designed, it can have approximately the same radiation efficiency (or even more).

However, because the antenna lengths are necessarily different, the radiation patterns will be different. For instance, while radiating exactly the same power, a 1/2WL resonant dipole and a non-resonant EDZ (1.25WL dipole) have different radiation patterns. The EDZ will best the 1/2WL dipole by ~3dB broadside but there is a direction at which the 1/2WL dipole will best the EDZ by ~3 dB. So your question cannot be answered as posed.
 
RE: A Tuner's Effect At The Antenna  
by WD8OYG on March 27, 2013 Mail this to a friend!
If a station in Buffalo, NY radiates two signals one through an auto tuner located at base of antenna and then sends the same signal with a tuner located at the xcvr location, will the signal level received be the same in Houston Texas for both of these signals?

Can we reliably predict and measure the difference, yes. Can we perceive it, probably not. So the answer is the signal will be very nearly the same with a couple of assumptions. First, the coax is RG-8 type (or better), less than 100 feet in length and the max SWR of the antenna is 10:1 or less.

Using math, we can see that the worst case would be for 30 MHz with a feedline loss of just under 2 db. With an S-unit being somewhere around 6 db, the difference would be one third of an S-unit on your meter. There may be some people that can hear the difference in one third or even a half of an S-unit, but probably not many.

Not surprising, AB4TAs real world measurements follow this very closely with his worst case at 30 MHz and a little over 2db of additional loss.

If you dont want to use math, look at the charts in the ARRL Handbook in the Transmission Lines section. First look up the line loss of RG-8 foam coax at 30 MHz (our worst case). It gives you about 0.9 db per hundred feet. Lets round it up to 1.0 db to make it easier.

Then go to the chart that shows the Additional Loss Caused by Standing Waves. Start at 1.0 db on the bottom (the loss of the coax) and move up the graph to the 10:1 SWR line (again, our worst case assumption). Then move to the left and you will see that additional loss will not be over about 1.5 db.

Measurable, yes. Perceivable, probably not.

Dwayne Kincaid WD8OYG
 
RE: A Tuner's Effect At The Antenna  
by AA4PB on March 27, 2013 Mail this to a friend!
"we can see that the worst case would be for 30 MHz"

Maybe, maybe not. It depends on the antenna. Take the case of a 20-foot vertical end-fed wire antenna. At 30MHz the matched loss will be greater than at 1.8MHz but at 1.8MHz the impedance mismatch will be greater. For that reason you may find the actual loss is greater on the lower frequencies.
 
RE: A Tuner's Effect At The Antenna  
by NZ5L on March 27, 2013 Mail this to a friend!
An excellant summation of the theory of the conjugate match! And, to one and all, I freely add the following: STOP WORRYING ABOUT YOUR SWR! A reasonable length of good quality feedline, such as LM-400, will have a negligable ADDITIONAL loss - under 1Db - even up to a 5:1 mismatch, at most HF frequencies, so there is no real need to put up separate dipoles or elaborate matching schemes at the antenna for the CW and SSB portions of the 3.5MHz band. And go right ahead and use your 40 Meter dipole on 15, with a good in-shack tuner.
Matching to 50 ohms DOES involve one other parameter of note,however - tuner loss. Often enough, a typical station will lose more signal (both ways) in a tuner than in a feedline, which is why it pays to have the best possible tuner. And avoid the ultra-compact designs at anything above QRP.
To all those who cling to "a tuner just keeps the transmitter happy" idea, I refer you back to the "MatchCom" antenna, also appearing under the name MatchAll, and others. This marvelous device was to be installed right at the feedpoint of a dipole, and would, with no moving parts or any kind of adjustment, provide a low SWR on any and all bands - wonderful, practically a reprieve from the tyrannical laws of physics! I'm sure it made the "no tuner" crowd very happy. Then came Lew McCoy's analysis in CQ magazine, dissecting it and finding - mirabile dictu! - a potted 50 ohm dummy load! Up until that time I'm sure they sold a few of these things, and they were not cheap. As for me, I'll stick with tuners.
 
RE: A Tuner's Effect At The Antenna  
by WD8OYG on March 27, 2013 Mail this to a friend!
"Maybe, maybe not. It depends on the antenna. Take the case of a 20-foot vertical end-fed wire antenna. At 30MHz the matched loss will be greater than at 1.8MHz but at 1.8MHz the impedance mismatch will be greater. For that reason you may find the actual loss is greater on the lower frequencies."

If we assume the SWR of the antenna at the feedpoint is 10:1 or less, the loss will never be more than 1.5 db. So the antenna type is not in the equation.

It would be correct to say that given the assumptions, it would be always be 1.5 db extra loss or less depending on the antenna.

Dwayne Kincaid WD8OYG
 
RE: A Tuner's Effect At The Antenna  
by AA4PB on March 27, 2013 Mail this to a friend!
"If we assume the SWR of the antenna at the feedpoint is 10:1 or less"

That may not be a valid assumption. With 50 Ohm coax, a 10:1 SWR is only 500 Ohms. A short antenna can easily be 1000 Ohms or more. At 1000 Ohms that's a 20:1 SWR. Now, because of the high loss you may read only 10:1 with an SWR meter located back at the tuner output. As I said, it all depends on the antenna and its actual feed impedance.

If you are feeding something like an inverted-L on all bands you can be a lot better off with something like an SGC remote tuner located outside directly at the antenna feed point rather than trying to directly feed it through 100-feet of 50 Ohm coax.

You have to analyze the whole proposed antenna system (tuner, feed line, antenna impedance on all bands, etc) rather than making assumptions and assuming that a tuner sitting next to the transmitter can "fix" any antenna.

 
RE: A Tuner's Effect At The Antenna  
by AA4PB on March 27, 2013 Mail this to a friend!
Actually, if you look at an analysis done on a 43-foot vertical fed directly with 75 feet of RG213 you find that the loss at 1.8 MHz is 18dB. At 28 MHz it is only 0.8 dB. The loss is higher on lower frequencies because of the high feed impedance when the antenna is shorter in terms of wavelength.

 
RE: A Tuner's Effect At The Antenna  
by G8HQP on March 27, 2013 Mail this to a friend!
The maximum power transfer theorem, although true, is irrelevant to this situation as even a Class A transmitter will normally be run in 'maximum efficiency' mode rather than maximum power mode.

I suspect that that the real issue is that there is confusion between 'source impedance' and 'optimum load impedance'. In the case of many transmitters, source impedance is not a well-defined concept. Even when it is, it is rarely equal to optimum load impedance. As G3RZP said, what about electrical generators - you definitely don't want maximum power transfer as the generator would quickly melt!

A tuner, wherever it is placed, provides to the transmitter the optimum load impedance. This allows the transmitter to provide the power intended at the efficiency intended. To talk about 'tuning' the transmitter or the antenna is a potentially misleading shorthand which does no harm provided nobody takes it too seriously.
 
A Tuner's Effect At The Antenna  
by NV2A on March 27, 2013 Mail this to a friend!
Thank you Cecil, that helped me a lot. You just saved me a lot of work for nothing !! I appreciate your effort.
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 27, 2013 Mail this to a friend!
> G8HQP wrote: A tuner, wherever it is placed, provides to the transmitter the optimum load impedance. <

Yes, but the question is: Is that all a tuner does? For a transmitter designed to drive a 50 ohm load, the tuner creates a 50 ohm Z0-match at the shack tuner input. The effect of that 50 ohm Z0-match ripples throughout an efficient low-loss system and establishes close to a 1:1 correspondence to the conditions of a system-wide conjugate match from the tuner input to the antenna feedpoint. Measurements taken anywhere between the 50 ohm Z0-match and the antenna feedpoint will indicate that the impedance looking in one direction is close to the conjugate of the impedance looking in the opposite direction. That's close enough to a conjugate match for me.
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by AI4WC on March 28, 2013 Mail this to a friend!
Maybe I have gotten simple with age, but wouldn't simply measuring the RF at the antenna solve the argument? No matter how you argue all these points, isn't this the "bottom line?" I tune my antenna as best I can, use the best and shortest coax, have a good "antenna tuner." What else can I do? Why worry? I will appreciate hearing if (why) I am "wrong."
73, and good DX
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 28, 2013 Mail this to a friend!
> AI4WC wrote: ... wouldn't simply measuring the RF at the antenna solve the argument? <

There is actually no argument - there is only myth vs real world measurements. In a low-loss antenna system, adjusting a tuner in the shack for an SWR of 1:1 (50 ohm Z0-match) on the tuner input, results in maximum voltage, current, and power measured *at the antenna feedpoint*. One can observe those measured values peaking at the antenna as the tuner in the shack achieves its match.
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by G8HQP on March 28, 2013 Mail this to a friend!
W5DXP said: Yes, but the question is: Is that all a tuner does?

Yes. The aim of a tuner is to present the Tx with the impedance it likes to see. Saying that this implies a conjugate match everywhere in the system assumes that the Tx has an output impedance which is equal to its optimum load impedance. This is not necessarily true, so your conjugate match idea is not necessarily true.

The impedances you see at some point in the cable, looking both ways, are not necessarily conjugates. One is the antenna, transformed by the cable (and the tuner, if it is at that end). The other is the Tx output impedance, transformed by the cable. Now swap the Tx for a different Tx with a different output impedance, yet requiring the same optimum load impedance. The 'antenna facing' impedance does not change. The 'Tx facing' impedance will change. If they were, coincidentally, conjugates then they won't be after the swap.

As often seems to be the case, people write articles to share their misconceptions with their readers!
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 28, 2013 Mail this to a friend!
> G8HQP wrote: The impedances you see at some point in the cable, looking both ways, are not necessarily conjugates. <

I see that I need to expand my article for the purists. I am somewhat enhancing/expanding the conjugate matching theorem.

If the SWR on the 50 ohm coax between the transmitter and the tuner is 1:1, the transmitter source impedance simply doesn't matter and can be replaced by a Thevenin equivalent source with a source impedance of 50 ohms.

Here are three sources:

1. 150 volt, 25 ohm source---50 ohm coax---x

2. 200 volt, 50 ohm source---50 ohm coax---x

3. 300 volt, 100 ohm source---50 ohm coax---x

Here is the load:

x-------1/2WL 450 ohm ladder-line------50 ohms

No matter which source is connected to the load, all the conditions between x and the 50 ohm load are identical. Since source number 2 provides a conjugate match, we can assert the following:

If the SWR on the coax is 1:1, all the load conditions between x and the 50 ohm load are identical to a conjugately matched system. Call it a quasi-conjugate match if that will make you feel better.

Here's the kicker: Since all conditions between x and the 50 ohm load are identical to a conjugately matched system, the impedance at any point in the forward and backward directions are conjugates of each other, i.e. all of the power available out of the coax is being delivered to the load and it is obvious that 200 watts is being delivered to the 50 ohm load in all cases.

I agree that technically cases 1 and 3 are not conjugately matched but I am asserting that it doesn't make any difference to the rest of the system since no reflected energy ever reaches any of the source impedances. Therefore, the source impedances are unknown and indeed irrelevant since they do not have any effect on the rest of the Z0-matched system.

So I am ready to restate something I asserted in a previous posting: If a 50 ohm Z0-match is achieved at the input of a tuner located in the shack, the effects of that 50 ohm Z0-match extend all the way to the antenna causing conditions to be identical to a conjugate match. Since all conditions from the tuner input to the antenna feedpoint are identical to a conjugate match, the unknown source impedance doesn't really matter.

In other words, try thinking outside the box since it seems to be impossible to measure (or model) the output impedance of a typical ham transmitter.
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by WD8OYG on March 28, 2013 Mail this to a friend!
@AA4PB What problem do you have with an assumption of 10:1 swr or less. Of course anything higher than that does not apply

@AI4WCYou cant measure the power at the feedpoint because almost all meters assume 50 ohm reference.

Cecil is correct, there is no perceivable difference of the tuner at the antenna or in the shack. Given the conjugate match, it will automatically provide the maximum power transfer. We proved this almost two decades ago using physics and no one can prove otherwise.

Dwayne Kincaid WD8OYG
 
RE: A Tuner's Effect At The Antenna  
by G8HQP on March 28, 2013 Mail this to a friend!
W5XDP said: I see that I need to expand my article for the purists. I am somewhat enhancing/expanding the conjugate matching theorem.

If knowing the difference between output impedance and optimum load impedance makes me a 'purist', then I am happy to wear that label. Being a 'purist' often helps me avoid making elementary mistakes.

I would prefer to say that you are somewhat confusing/misrepresenting the conjugate matching theorem by asserting that there is a conjugate match when there is not a conjugate match. I guess knowing the difference between 'is' and 'is not' makes me a purist.
 
RE: A Tuner's Effect At The Antenna  
by AA4PB on March 28, 2013 Mail this to a friend!
@AA4PB What problem do you have with an assumption of 10:1 swr or less.

The problem is that you cannot assume that ALL antenna types will have an SWR of 10:1 or less on all frequencies. As I stated, a short vertical (short in terms of wavelength) fed with 50 Ohm coax can have an SWR much higher than 10:1 resulting in losses in excess of 20dB, which I would not consider insignificant.

 
RE: A Tuner's Effect At The Antenna  
by WD8OYG on March 28, 2013 Mail this to a friend!
Correct and you would not use a 10:1 tuner as implied by the article.

Your choice of parameters is outside the scope of this discussion.

Dwayne Kincaid WD8OYG
 
RE: A Tuner's Effect At The Antenna  
by N4JTE on March 28, 2013 Mail this to a friend!
Cecil is my go to guy for anything transmission line related and has answered many questions for me and countless others.
Appreciate your experiments and this article Cecil, as they say build it and they will come, hi.
Best regards,
Bob
 
RE: A Tuner's Effect At The Antenna  
by AA4PB on March 28, 2013 Mail this to a friend!
Well the article assumes a transmission line loss of 0dB too. That's fine for discussion purposes but it doesn't mean that you can assume negligable transmission line losses in all real world cases.

My point was that there are cases where moving the tuner out to the antenna feed point can reduce the real world transmission line losses very signifcantly.
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 28, 2013 Mail this to a friend!
> G8HQP wrote: ... by asserting that there is a conjugate match when there is not a conjugate match.<

Since the conjugate matching theorem assumes lossless transmission lines which cannot exist in reality, I would be an absolute fool to assert that a conjugate match is even possible in the real world. Please try a different attack next time.
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 29, 2013 Mail this to a friend!
> G8HQP wrote: As often seems to be the case, people write articles to share their misconceptions with their readers! <

I'm not trying to promote or share any misconceptions. I am instead trying to promote an accommodation between ideal theory and less than ideal real world practice. Here are a number of those accommodations:

1. Transmission line theory usually begins with lossless transmission lines even though they cannot exist in the real world. Often, a lossless analysis of a low-loss system gets us close enough to the real world solution to be acceptable within the limits of engineering accuracy.

2. SWR circles on a Smith Chart are a useful concept even though they cannot exist in the real world. In the real world, they are SWR spirals that would eventually wind up at the center of the chart.

3. The concept that an impedance repeats every half wavelength in a transmission line is useful even though it is technically not true.

4. The conjugate matching theorem requires that all networks between the source and the load, including transmission lines, be lossless. Therefore, system-wide conjugate matches are impossible in the real world. That doesn't prohibit a "conjugate match" from being a useful concept.

I am proposing that we draw a box around a system and analyze what is in the box. On one side of the box is the shack tuner input (source) and on the other side of the box is the antenna feedpoint (load). We call the signal at the tuner input "the source of available power". In a low-loss system, when the tuner is adjusted for maximum available power being delivered to the antenna, a 50 ohm Z0-match is formed at the tuner input and the conditions inside the box are virtually identical to a conjugate match. I call it a "virtual conjugate match" since it walks and quacks like a conjugate match and find it to be a useful conceptual accommodation to the real world. (I got the word "virtual" from Walter Maxwell.)
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by AI4WC on March 29, 2013 Mail this to a friend!
Thanks, folks. I like ham radio because we can interact with many thoughtful (read that as deep-thinking) people on technical subjects. I think I always learn something, if it is only just that things aren't that simple. Most of all, I appreciate everyone (practically) keeping the discussions civil. That way, we all can participate. And, thanks, Cecil for a good article.
Thanks & 73,
AI4WC
 
RE: A Tuner's Effect At The Antenna  
by G8HQP on March 29, 2013 Mail this to a friend!
No conjugate match, except in the situation where the transmitter output impedance and its optimum load impedance happen to be the same (or conjugates).

To show that this is the case, simple assume a negligibly short transmission line. Sit in the middle of this line. Looking either way you don't see a conjugate match, virtual or otherwise. You see the Tx one way, and the antenna the other way.

Retreating into excuses about combining the real world with theory won't wash. Your basic thesis is wrong. As I said, article writers often like to share their misconceptions. That is why there are so many misconceptions around. People assume, wrongly, that authors (and magazine editors) know what they are talking about.

Please retract your article. This is not an attack on you, but a criticism of your article - on the simple grounds that its central thesis is wrong.
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 29, 2013 Mail this to a friend!
> G8HQP Please retract your article. This is not an attack on you, but a criticism of your article - on the simple grounds that its central thesis is wrong. <

The central thesis is: A tuner in the shack causes measurable changes at the antenna feedpoint. If you think that is wrong, please perform the measurements for yourself.

In case you mistakenly believe the central issue is conjugate matching, here are my thoughts.

A system-wide conjugate match is impossible in the real world because of losses and non-linearity which are not allowed by the conjugate matching theorem. The closest we can come in a real world system is something that somewhat resembles parts of a conjugately matched system.

Nobody knows for sure what the source impedance of an amateur radio transmitter really is so it is illogical to try to apply the conjugate matching theorem, as it exists, to an amateur radio transmitter. But instead of throwing the baby out with the bath water, maybe we can salvage some usefulness from the concept of conjugate matching.

If we replace the transmitter that is supplying power to the system with a source known to be conjugately matched *AND NOTHING CHANGES*, i.e. there is a *one-to-one correspondence* to a conjugately matched system, we can say the the system outside of the source resembles, i.e. is similar to a conjugately matched system.

When we achieve a 50 ohm Z0-match at the input terminal of an antenna tuner in the shack (fed with 50 ohm coax) we have isolated the source from any incident reflected energy and have no way of knowing what the source impedance really is because it has no effect on the rest of the system and we cannot tell one source impedance from another. Any source designed to drive a 50 ohm load will supply a signal where V/I=50 ohms into the coax-fed 50 ohm Z0-match at the tuner input. No matter what the source impedance, the rest of the low-loss system resembles a near-conjugately matched system, i.e. it walks and quacks like a conjugately matched system from the tuner input to the antenna feedpoint. No, it is not necessarily conjugately matched but it supports a *one-to-one correspondence* to a conjugately matched system so it resembles a conjugately matched system. That is an important mathematical concept often used to prove identity or similarity.
--
73, Cecil, w5dxp.com
 
A Tuner's Effect At The Antenna  
by KA9HJZ on March 30, 2013 Mail this to a friend!
Nice article but i already new that a tuner basically only satifies the transmitter. i have a small lot and i like to operate on different bands and different frequencies. my transmitter finals are expensive and a pain to replace. So i have a tuner. it works for me and i never have a problem makeing contacts with 50 watts or 5 watts. i do CW and have had enough contacts from all over the world. as an old Army CW radio operator, most of the time all we had was a verticle antenna on our 3/4 ton radio truck or a long wire thrown up into a tree with a linemans pliers as a weight. have fun is my motto.
 
A Tuner's Effect At The Antenna  
by KD7HXN on March 30, 2013 Mail this to a friend!
Even tho I have an advance ticket my antenna knowledge is very spotty - the math is a sticker for me. Is there math book/course specific to radio that starts at zero and works up to working knowledge?
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 30, 2013 Mail this to a friend!
> KA9HJZ wrote: Nice article but i already new that a tuner basically only satifies the transmitter. <

If a tuner "only satisfies the transmitter", i.e. has no effect at the antenna, can anyone tell me why the measured field strength radiated from my *antenna* increases in magnitude when the tuner is adjusted to a match? Seems to me the effect at the antenna, the source of our radiated signal, is more important that the effect on the transmitter.

Indeed, one can often increase the measured radiated power by de-tuning the antenna tuner away from the 50 ohm Z0-match point. Two possible reasons for such is that (1) the transmitter may be "happier":) while outputting more power into a load other than 50 ohms and (2) the antenna may radiate more power with a conjugate match at the antenna feedpoint rather than a match back in the shack.

Note that even though a system-wide conjugate match is impossible in the real world, it is still possible to achieve a conjugate match at a *point* in the system, e.g. at the antenna feedpoint.
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by K9MHZ on March 30, 2013 Mail this to a friend!
>>>>by G8HQP on March 28, 2013
W5DXP said: Yes, but the question is: Is that all a tuner does?

Yes. The aim of a tuner is to present the Tx with the impedance it likes to see. Saying that this implies a conjugate match everywhere in the system assumes that the Tx has an output impedance which is equal to its optimum load impedance. This is not necessarily true, so your conjugate match idea is not necessarily true.<<<<



Yes, but it's not "necessarily" false, either. I hope you're not implying that in ALL cases it's not true. I think the disconnect between you and Cecil is an examination of what exists downstream of the tuner....it's not ALL a mess if it's reasonable, and yes it DOES matter what's beyond the tuner. I'd agree that too many people get locked into the notion that just about anything beyond the tuner is OK.....have a look at Isotron antennas, good grief.

For so long, a certain U.S. ham would come on here and lecture people about tuners, even going so far to beat them up on their use of the word "tuner" versus "tansmatch" or whatever. Anyway, his assertions were very similar to yours, stating that tuners are just essentially a gimmick to show the transmitter 50 ohms, and that everything downstream of the tuner is just a mess, and even stating that the reflected power radiating off of the coax shield was doing good work and still better than using a tuner. Someone later presented something similar to Cecil's, and I haven't seen Alan back yet (thankfully).

As with most things in life, the reasonable setup wins.



 
RE: A Tuner's Effect At The Antenna  
by W5DXP on March 30, 2013 Mail this to a friend!
K9MHZ wrote: I think the disconnect between you and Cecil is an examination of what exists downstream of the tuner...<

Seems to me the major problem is that after I have asserted many times that a system-wide conjugate is impossible in the real world, I still get accused of saying a conjugate match actually exists which is obviously a falsehood. Maybe words don't mean the same thing in English as they mean in Texan?:)
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by KI5FJ on March 31, 2013 Mail this to a friend!
Radiated Field Strength is maximum when maximum power is being transfered from the TX to the antenna.
This ideal condition occurs when the SWR is low at the TX. Another indication of efficient matching is when antenna current is peaked. Sometimes a ATU match will not be the most efficient possible. I suggest if you observe multiple acceptable matching settings chose the one with maximum capacitance. 73 Joe O, NNNN
 
A Tuner's Effect At The Antenna  
by K1DA on March 31, 2013 Mail this to a friend!
And the next part of this to rear its' ugly head will be "Err Hiram, ya can't got OUT if your antenna ain't RESONANT".
 
A Tuner's Effect At The Antenna  
by K1DA on March 31, 2013 Mail this to a friend!
BTW, this discussion seems to discount the effects of foldback circuits in "50 ohm" solid state transmitters. Looking at current drawn by the transmitter, and a trusty old field strength meter will often suggest that maxium radiated signal strength is related to how much current the transmitter draws, and twisting the tuner knobs for max field strength usually gets you to the max current point. Interesting experiments can be done with a 100 watt solid state transmitter run at one or two watts out, such transmitters are usually content to produce low power irrespective of the load they see, thus negating the effects of foldbacks.
 
RE: A Tuner's Effect At The Antenna  
by W7NUW on March 31, 2013 Mail this to a friend!
An old tricky question about power transfer:

You have a load resistance = 50 ohms. And you have a generator with internal resistance = Rg.

Question: What value of Rg will produce maximum power transfer to the load?

NOT 50 ohms!

ZERO ohms!

If your amp is "conjugate matched" to a 50-j0 antenna, or the input of a tuner that "transforms" the antenna to 50-j0 ohms, you will dissipate as much power in the transmitter as you deliver to the antenna (or tuner). The amp is designed to have as close to zero ohms output impedance as possible. Whatever non-zero internal resistance it has just heats your shack.

I am using a 600 watt amp that is 'putting out' 600 watts. I'm not dissipating 600 watts in the amp.

Ken W7NUW

 
RE: A Tuner's Effect At The Antenna  
by W5DXP on April 1, 2013 Mail this to a friend!
> W7NUW wrote: Question: What value of Rg will produce maximum power transfer to the load?<

Sorry, that is not how the maximum power theorem is stated. Boundary conditions state that Zsource is fixed at a positive Rs (or Rs+jXs) value and Rload (or Zload) is varied.

Here's how to ask the question: *GIVEN A FIXED SOURCE IMPEDANCE* where Zsource > 0, what is the value of load impedance that will cause maximum power transfer?
--
73, Cecil, w5dxp
 
RE: A Tuner's Effect At The Antenna  
by WB4JZY on April 1, 2013 Mail this to a friend!
does in fact 50% of the power get dissipated in the source??
 
RE: A Tuner's Effect At The Antenna  
by AA4PB on April 1, 2013 Mail this to a friend!
The typical 100W transceiver draws about 20A peak during transmit. Allowing 5W for driver stages lets say the PA itself draws 15A @ 13.8V or 207W. 207W input for 100W output means that yes, about one-half of the peak DC input power is being disipated in the PA. Thats why there are big heat sinks on the radios.
 
RE: A Tuner's Effect At The Antenna  
by AA4PB on April 1, 2013 Mail this to a friend!
With simple Ohm's law one can see that even with DC circuits the maximum **POWER** is transferred to a load when the load resistance is equal to the internal source resistance so that the source and load are disipating equal amounts of power.
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on April 1, 2013 Mail this to a friend!
> WB4JZY wrote: does in fact 50% of the power get dissipated in the source?? <

The maximum power transfer theorem is conditional on the source impedance being linear, non-zero/negative, and dissipative.

Those conditions do not apply to the average ham radio transmitter, e.g. a class-C amplifier is obviously non-linear and coincidentally has an efficiency greater than 50%. Most of our so-called linear amplifiers have each individual output transistor operating under non-linear cutoff conditions during some percentage of the RF cycle.

The best we can do for most ham transmitters is to pick a point, usually after the low-pass filter, where the source signal is linear and consider whatever that value of V/I is, to be the linear source impedance - and replace the non-linear transmitter with a linear Thevenin equivalent. Given that assumption, we can then look for conjugate-match-like conditions in the external networks where we can talk about the transfer of maximum *AVAILABLE* power. That's the approach that Walter Maxwell used.
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by W7NUW on April 1, 2013 Mail this to a friend!
I realize this is not how the "maximum power theorem is stated." That's not my point.

My 'tricky' question is meant as a thought experiment. If the question is "What value of a generator's internal resistance produces the maximum power to a load?" the answer is clearly zero ohms.

A small space heater might be a 10 ohm load to your house wiring (120^2/10 = 1440 watts). You don't ask the power company to put a 10 ohm resistor in your service entry to get "maximum power transfer."

Whether you are designing the power grid, a battery, or any other kind of power source, the most efficiency is obtained when the internal resistance is minimized. Zero, in practice, is of course never achieved.

73, Ken W7NUW



 
RE: A Tuner's Effect At The Antenna  
by W5DXP on April 1, 2013 Mail this to a friend!
> W7NUW wrote: Whether you are designing the power grid, a battery, or any other kind of power source, the most efficiency is obtained when the internal resistance is minimized. <

True, but the maximum power transfer theorem is not about efficiency. The maximum power transfer theorem implies that the most power would be transferred from a zero ohm source into a zero ohm load with an infinite current, i.e. infinity squared times zero. In math, we call such a condition "undefined" as the squaring of infinity overwhelms the multiplication by zero.:)
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by AA4PB on April 1, 2013 Mail this to a friend!
Take a look at:
http://en.wikipedia.org/wiki/Maximum_power_theorem

With a source resistance of zero Ohms there is ALWAYS zero power disipated in the load so 100% of the power is transferred to the load. For any source with some internal resistance, maximum power transfer occurs when the load resistance equals the internal source resistance.

In the case of the electric heater you are NOT seeking maximum power transfer. If you did, that would imply that 50% of the power capacity of the generator plant (less what is disipated in the line resistance) would be transferred into your heater. It would get very hot indeed!

You are looking at the theorm backwards. You don't adjust the source resistance to match the load resistance because that would just increase system loss. However, given a fixed source resistance if you adjust the load resistance to match the source resistance then you get the highest possible power transferred to the load. Half the generator power output is disipated in the internal source resistance and half is disipated in the load. That's the best that you can do in terms of power transfer.

Maximum power transfer does NOT mean maximum efficiency. Maximum efficiency occurs when the source resistance is small compaired to the load resistance. The load resistance represents the work you want to do while the source resistance represents power lost. Remember, a generator only creates as much power as the load will accept. A 75AH battery outputs zero power if there is no load. Your 100W transmitter outputs zero power if the load impedance is infinite.
 
RE: A Tuner's Effect At The Antenna  
by AA4PB on April 2, 2013 Mail this to a friend!
Correction: With a source resistance of zero Ohms there is ALWAYS zero power disipated in the source so 100% of the power is transferred to the load.
 
RE: A Tuner's Effect At The Antenna  
by W7NUW on April 2, 2013 Mail this to a friend!
AA4PB -- I am not "looking at the theorem backwards". I am ignoring the theory because it mostly doesn't apply to the discussion thread. I agree with everything else you have said, but am trying (have been from the start) to drive home the point: that it is silly to make the power source's internal resistance equal to the load's.

Exactly as you put it: "You don't adjust the source resistance to match the load resistance because that would just increase system loss."

Many comments by others suggest a failure to understand this. Even my amp's spec sheet states the output impedance of the amp (Tokyo Hy-Power HL-1.2Kfx) is 50 ohms. I don't believe this. They should be saying that the amp is designed to work INTO 50 ohms. This is the impedance that its voltage and current capabilities can handle at its rated (600 watt) level -- about 170 volts and 3.5 amps (RMS).

The discussion has also been confused by the introduction of issues of efficiency in Class C and Class A amps. The efficiency of these configurations has nothing to do with SWR and line/antenna "matching".

The most efficient amplifier is Class D (hard zero to hard drive voltage). As close to zero ohms as you can get.

Ken W7NUW

 
A Tuner's Effect At The Antenna  
by AF7AD on April 8, 2013 Mail this to a friend!
Another interesting insight:
http://vk1od.net/transmissionline/folla/index.htm
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on April 9, 2013 Mail this to a friend!
What can I say? I have said before and freely admit that a lossless analysis fails in the real world and fails miserably for lossy systems. Owen's example has 44% losses so it is just another lossy straw man example designed to prove something to which my article doesn't apply. Perhaps I should have said that I was talking only about real world systems that are within 10% of an ideal conjugate match? I will add that disclaimer to the revised article on my web page.

Here's a better example of what I was talking about using VK1OD's own transmission line calculator at:

http://www.vk1od.net/calc/tl/tllc.php

Assume an antenna with a feedpoint impedance of 102-j480 ohms used on 14.2 MHz. Feed the antenna with 69.4 feet of "open/air dielectric 150/2" from Owen's menu of transmission lines. The impedance looking into the transmission line at the shack end will be 105-j467 ohms according to Owen's calculator. If we want to resonate the system at the antenna feedpoint, we install a +j480 ohm loading coil. If we want to resonate the system at the shack end, we install a +j467 ohm loading coil. That's a ~3% difference in impedances. In fact, the same loading coil will work pretty well at both ends. It's certainly not a perfect result but I don't require or expect perfection from the real world. 10% is usually good enough for me. Heck, I remember when standard resistors were spec'ed at 20% accuracy.
--
73, Cecil, w5dxp.com
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on April 10, 2013 Mail this to a friend!
VK1OD's article, "The failure of lossless line analysis in the real world", written as a rebuttal to my Old Wives' Tale article is nothing but a straw man argument since I have already written (and everybody knows) that a lossless line and a conjugate match are impossible in the real world. The following quote from the VK1OD web page illustrates a typical straw man argument.

[quote]The question is "does the "antenna tuner" ha[ve] the same effect whether it is located at the load or at the source" in the real world?[/quote]

No, that is not the question. That straw man question is pulled out of someone's vivid imagination. Here is the logical step that I am asserting and asking people to take:
------------
Given: In a lossless system, an antenna tuner has the same effect whether it is located at the load or source.

Question: In a system with losses, does an antenna tuner located at the source have SOME effect at the load - not the same effect as in a lossless system, but ANY effect at all at the load?

Answer (next to last paragraph of my article): "One can see for oneself the effect that an antenna tuner has at the antenna. Install a dummy load on the tuner input and at the antenna feedpoint, disconnect the feedline and connect it an antenna analyzer. Have someone twist the knobs on the tuner and observe the impedance change at the antenna. Then who can truthfully say that an antenna tuner has no effect at the antenna?"
------------
I never asserted nor did I ever attempt to prove that, in a system with losses, the antenna tuner has the SAME effect whether located at the load or at the source. If an antenna tuner at the source has ANY effect at all at the load, then the title of my article is indeed an Old Wives' Tale.

In fact, the ONLY reference I make to the real world is in that next to last paragraph of my article quoted above. I certainly don't see anything in that paragraph that resembles what VK1OD mistakenly alleges that I have said about systems with losses. Since one can measure the effect that a tuner, located at the source, has at the antenna, then the Old Wives' Tale is proven to be a myth.

The fact that VK1OD wasted so much time and effort on a straw man argument is sad. We shall see if he revises the article to reflect my actual assertions instead of ones he made up out of thin air.

These eHam.net articles cannot easily be replaced by a revision. What I do is publish rev. 1.0 of the article on eHam.net and then post revisions to the article on my web page. This revised article will be published on my web page as:

http://www.w5dxp.com/OWT1.htm
--
73, Cecil, w5dxp.com
 
A Tuner's Effect At The Antenna  
by W3TTT on April 10, 2013 Mail this to a friend!
Great article!
I have been using a tuner for years now, and my transmitter and I are very happy.

AA4PB - please notice that the article did not mention SWR. SWR is meaningless in this context. You tune for lowest SWR, yes, but when you get a 1:1 that just means that you have tuned out any impedances and now have a conjugate match.

W5DXP - How do you calculate a conjugate match for electrically short antennas that have a low radiation resistance? Instead of 50+j200 you would have 2+j1000. YOu would need to match the real portion of the antenna as well as the imaginary portion. Also, how would you do the same for a random length of transmission line? I rarely have an exact multiple of wavelength of line.
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on April 10, 2013 Mail this to a friend!
Technical questions that are outside the scope of the article are best asked on the newsgroups. My rule-of-thumb would be: Choose a dipole length that is at least 3/8WL on the lowest frequency of operation and adjust the ladder-line length for a match. Here's an example:

http://www.w5dxp.com/notuner.htm

I would avoid impedances such as 2+j1000 ohms like the plague.:)

Here's something else that might help:

http://www.w5dxp.com/goodbad.htm
 
A Tuner's Effect At The Antenna  
by N4BWV on April 11, 2013 Mail this to a friend!
The bottom line is that an antenna tuner cannot change feed line loss but they do make it possible to pump more RF into the antenna. Correct?
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on April 11, 2013 Mail this to a friend!
Yes, but note that the more RF energy that one supplies to the antenna, the higher is the *magnitude* of the feedline losses.
 
RE: A Tuner's Effect At The Antenna  
by KD0CAC on April 16, 2013 Mail this to a friend!
Trying to take this in with the lack of knowledge [ hopefully added a little each time I read some of these articles ] .
So my take on this is to match the feedline to what I want my rig and antenna to do ?
As an example , if I could have an antenna farm , separate antennas - feedlines for each band .
It gets tricky when I want a multiband antenna , so the need for an adjustable feedline ? :)
So now if winter ever quits here , I wanted to put back the loading coil at the base of my Butternut HF9 .
Because I elevated the HF9 to about 20' and built my own CPK - counterpoise , and the directions from the CPK said to remove the 75 ohm matching cable & the loading coil .
So now I will not wait for the weather , I will just add the loading coil in the shack ?
Good thing propagation is bad the last few days , I can do more reading about making my station perform better .
Thanks
John
 
A Tuner's Effect At The Antenna  
by K7PHX on April 19, 2013 Mail this to a friend!
Debunking old wives' tales can be helpful, but this article introduces new ones to those already in existence. Thank you for the instructive math problems. I think we are all aware that impedance matching actually means complex conjugate.

"Making the transmitter happy" acquired more important meaning with the advent of solid state PA's. The smaller transceivers did not have room for large output networks and PA transistors cannot take the beating that tube output stages can do. Thus, hams had to consider a tuner at the transmitter to protect the PA stages from damage due to potentially destructive voltages and currents on a mismatched line.

It is gratuitous to point out that any given impedance vector has its complex conjugate. And it should also be obvious that a tuner at the transmitter will also affect the entire antenna system. But we should not for a minute pretend that the transmitter tuner magically transforms a given system into an efficient transmitting antenna.

Assuming a distant antenna with feedline connection, radiation resistance is maximized when the antenna is resonant (i.e. no reactive component) and matched to the transmission line at the feed point.

The job of a transmitter tuner is to keep the transmitter final from damage. As far as the transmitter is concerned it "sees" a matched resistive load. But, without attention to antenna resonance and feedline characteristic impedance, everything beyond the tuner becomes "the antenna". Enough rf may radiate from such a system to be workable. However the transmitter tuner has done nothing to create an efficient antenna system.
 
RE: A Tuner's Effect At The Antenna  
by W5DXP on April 19, 2013 Mail this to a friend!
> K7PHX wrote: Assuming a distant antenna with feedline connection, radiation resistance is maximized when the antenna is resonant (i.e. no reactive component) and matched to the transmission line at the feed point. <

So you are going on the record asserting that a 1/2WL resonant dipole radiates better than a 1.25WL non-resonant Extended Double Zepp? Hint: It is easy to prove that a coax-fed 1/2WL dipole is inferior to an open-wire fed EDZ.

What you seem to be missing is that exactly the same neutralization of the reactive component happens when a conjugate match is achieved at the antenna feedpoint whether the antenna is a resonant length or not.

Resonant Case 1: The feedpoint of the 1/2WL dipole is 50+j0 ohms and the impedance looking back toward the source is 50-j0 ohms. The antenna is accepting 100 watts from the coaxial transmission line.

Non-Resonant Case 2: The feedpoint of the EDZ antenna is 175-j1000 ohms and the impedance looking back toward the source is 175+j1000 ohms. The antenna is accepting 100 watts from the open-wire transmission line.

Both systems are conjugately matched at the feedpoint.

Assuming the efficiency of the two antennas are the same, they will radiate exactly the same amount of power. Such is easy to prove using the maximum power transfer theorem.

Moral: A conjugate match at the feedpoint of an antenna will match any reasonable radiation resistance and neutralize any reasonable reactance rendering any difference between a resonant antenna and a non-resonant antenna undetectable by an isolated operator.

Proof: Assume you are in a room with a 600 ohm open-wire transmission line coming through a hole in the wall. You measure 50+j0 ohms as the impedance looking into the open-wire line at the operating frequency.

Question: Is the antenna resonant or non-resonant?
--
73, Cecil, w5dxp.com
 
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