Transfer of power with an antenna tuner

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KQ4BX

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If you have an antenna tuner, and your antenna is a 10:1 match for your frequency, and the tuner brings it down to 1.2:1, do you get the same, or close to the same transfer of power to the antenna as you would if the antenna was a true 1.2:1?

I have more to say on this, but I want to see what everyone believes to know about this subject.
 

elk2370bruce

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Your transmatch (tuner) is designed to establish the best match between the antnna and radio so the simplistic answer to your question is yes. You might wish to review the construction specs on your antenna with regard to recommended feed line (coax, ladder line, etc. Maybe your problem lies in that area.
 

cmdrwill

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A mismatch IS a mismatch, the 'antenna tuner' just masks the mismatch.

Using a RF transformer is a better way to match something.
 

prcguy

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Antenna tuners have loss, some from wire resistance, some from stray capacitance, etc. The coil inside the tuner, whether its tapped or variable has an unused portion (which varies with size depending on band used) with RF on it that just flaps around and has capacitance to the inside of the case or ground. If your matching a very low impedance you can have more current in the coil and more resistive loss.

Some tuners are better than others and the Collins 180S-1 was tested as one of the more efficient designs. Some newer relay switched L/C tuners have a lot of loss in long circuit board traces and measure more than a dB in the straight through path.

You also have to discuss tuner loss separate from antenna system loss with a tuner. You can terminate a tuner with various resistor values and measure RF voltage and current to see if what comes out is close to what goes in. That may vary depending on the tuner configuration and if your tuning a high or low impedance load. If there is coax between the tuner and antenna that can add lots of loss in the antenna system.

Even with all that, if you use a tuner to fix say a 10:1 match between the coax and antenna, the radio will see a good match to the tuner and will be happy. The RF between the antenna and tuner will reflect from the antenna to the tuner then back to the antenna to be radiated with the same percentage reflected back to the tuner again in an endless dance as long as you are transmitting. If the loss in coax or whatever between the tuner and antenna is small then you will eventually radiate most if not all the power presented to the antenna after the tuner.

If there is loss in coax between the tuner and antenna then you will incur 2-way round trip loss when the RF is reflected from the antenna back to the tuner then back towards the antenna and some is radiated and some is reflected back again to incur more loss, etc, etc.

To end my rambling, if you have a dipole fed with low loss balanced line from a tuner, you will usually radiate a very high percentage of what the radio puts out. If you have a dipole fed with coax and use it way out of band and try to fix that with a tuner you can loose a lot.
prcguy
 
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n5ims

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Also remember that often a badly matched antenna (even if the tuner does a good job of fixing the match from the radio to the feedline) is generally an inefficient antenna. It may radiate your signal, but the pattern may be something totally weird and unexpected (e.g. you could talk to the moon, but not down the street).
 

KQ4BX

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Yes, it seams that we all know that the tuner becomes part of the antenna system, and since it is all in a metal box, it does not radiate, or make the antenna better at radiating than it is, it just protects the transmitter from an impendence mismatch. The best place for a tuner is on the antenna, not the feed line, unless the feed line is balanced line. So when LDG told me that my new tuner will work up to 10:1, I thought that they were counting on a bunch of idiots buying their tuner. Most radios with built-in tuners will match 3:1 or better, that is a more realistic approach to what a tuner should have to do. Yet when some hams review a radio with a built-in tuner, they criticize the tuner for only being 3:1 or better. As Hams, we are supposed to know how to build a resonant antenna, and those of us who buy the antenna, expect that it will be resonant. So where did LDG get the notion that Hams need an auto tuner that can handle 10:1 or better. Does this go back to what some old hams brag about? everyone must have heard of some old ham using their monster manual tuner to tune a fence, or an umbrella, or some other odd metal object, and making a load of contacts with it? Lest they forget that millions, and millions of contacts have been made on 5 watts or less. So when they pump the full legal limit into a fence, I'm sure that their tuner was heating up while it was eating 98% of their power.
So that was the argument I had with another ham, I insisted that the tuner would get hot, and the heat is because the tuner is consuming the power that does not make it out to the antenna. The other side of this argument said that the tuner made the antenna a better match for a full transfer of power to the antenna. Wrong I said, think of what a Transformer does, and how it gets warm. The transformer is as perfect as it can be, so the match is as good as it can be considering the match they are making, yet it still gets warm in the process of lowering or raising the voltage.
Then I mentioned the dummy load, and how it makes the transmitter happy by being 50 ohms. yet if you put that dummy load in open air, it will transmit, but not very well. That's because the dummy load will eat most of the power and turn that power into heat. All of this is within our direct control, once the signal leaves, it is out of our control.
 

prcguy

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A tuner that will handle or match a 10:1 VSWR or better is a very good thing to have in my opinion. Take for example my every day wire antenna, a 94ft flat top dipole at about 35ft fed with a critical length of 450 ohm ladder line (about 40ft) then a 25ft run of LMR-400 to the tuner. This antenna is known as a ZS6BKW and has a very good match on most bands 40m on up but a lousy match on 80m at around 7 to 10:1.

This antenna is fairly large and about 70% of a full size 80m dipole and probably within a dB or so in efficiency of a full size 80m dipole but the VSWR is high there. Since it’s fed with very low loss balanced line then a very short run of low loss coax, the feedline loss under mismatch condition is almost insignificant. My tuner has some loss in matching this antenna on 80m but in the end my performance on 80m is about the same as anyone else in my area running a full size 80m dipole at the same height.

Take the typical G5RV with slightly lossier 300 ohm twinlead then 100ft of RG-8X or even RG-58 and now you have some extra bonus loss adding up from the smaller coax being used under high VSWR conditions. The match on 80m will be better than my ZS6BKW and easier to handle by tuners internal to radios but at the cost of power wasted in feedline loss.

This loss will be far above the published loss per foot for the coax used and will degrade the first cycle of the signal to the antenna plus the reflected power back to the tuner then that same power reflected back towards the antenna, etc.

Big wire antennas fed with low loss and especially balanced feedline are very forgiving to VSWR but try feeding a short loaded vertical fed with lots of coax out of band and that will not work very well. Same thing with trying to use an 80m coax fed dipole on 40m where the feedpoint impedance will be extremely high or a 40m coax fed dipole on 80m, even though a tuner might fix the match it will not radiate very well.

So, a 10:1 rated tuner can not only allow you to use the radio on antennas with less than perfect matches, it can also get almost all that power radiated depending on the type of antenna and feedline. I would rather have the wide tuning range capability than not.
prcguy




Yes, it seams that we all know that the tuner becomes part of the antenna system, and since it is all in a metal box, it does not radiate, or make the antenna better at radiating than it is, it just protects the transmitter from an impendence mismatch. The best place for a tuner is on the antenna, not the feed line, unless the feed line is balanced line. So when LDG told me that my new tuner will work up to 10:1, I thought that they were counting on a bunch of idiots buying their tuner. Most radios with built-in tuners will match 3:1 or better, that is a more realistic approach to what a tuner should have to do. Yet when some hams review a radio with a built-in tuner, they criticize the tuner for only being 3:1 or better. As Hams, we are supposed to know how to build a resonant antenna, and those of us who buy the antenna, expect that it will be resonant. So where did LDG get the notion that Hams need an auto tuner that can handle 10:1 or better. Does this go back to what some old hams brag about? everyone must have heard of some old ham using their monster manual tuner to tune a fence, or an umbrella, or some other odd metal object, and making a load of contacts with it? Lest they forget that millions, and millions of contacts have been made on 5 watts or less. So when they pump the full legal limit into a fence, I'm sure that their tuner was heating up while it was eating 98% of their power.
So that was the argument I had with another ham, I insisted that the tuner would get hot, and the heat is because the tuner is consuming the power that does not make it out to the antenna. The other side of this argument said that the tuner made the antenna a better match for a full transfer of power to the antenna. Wrong I said, think of what a Transformer does, and how it gets warm. The transformer is as perfect as it can be, so the match is as good as it can be considering the match they are making, yet it still gets warm in the process of lowering or raising the voltage.
Then I mentioned the dummy load, and how it makes the transmitter happy by being 50 ohms. yet if you put that dummy load in open air, it will transmit, but not very well. That's because the dummy load will eat most of the power and turn that power into heat. All of this is within our direct control, once the signal leaves, it is out of our control.
 

vagrant

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So, a 10:1 rated tuner can not only allow you to use the radio on antennas with less than perfect matches, it can also get almost all that power radiated depending on the type of antenna and feedline. I would rather have the wide tuning range capability than not.
prcguy
Indeed, my 480SAT and a 66 foot OCF would not work 80 meters. An LDG KT-100 provided me with another band.
 

zz0468

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If you have an antenna tuner, and your antenna is a 10:1 match for your frequency, and the tuner brings it down to 1.2:1, do you get the same, or close to the same transfer of power to the antenna as you would if the antenna was a true 1.2:1?
It depends. You didn't give us enough information to expound upon that specific question.

You got some good answers from people, but the salient point is, the antenna begins at the last lumped component in the tuner. What your RF energy has to go through to actually get radiated once it's in the "antenna" would dictate the answer to that question.

The last paragraph of prcguy's first post is a nice summary of the situation.

SGC has an interesting view of antenna tuners that's worth repeating. They refer to their tuners as "antenna couplers". It's a recognition of the fact that the antenna starts on the circuit board of the coupler, inside the box. From that point on, the RF is radiating and wants to get out. If you force it through a piece of coax at that point, efficiency goes way down, and power is converted to heat.

If your antenna coupler is operated in a manner that it functions as an impedance matching devicer at the feedpoint of the antenna, and doesn't attempt to tune a piece of 50 ohm coax, then, most of your RF power will get radiated, and losses are mostly reduced to ohmic losses, as opposed to high VSWR losses in coax.

Look at the gamma match on a yagi. It's an impedance matching device as well as a balun, but it's not traditionally looked upon as a major source of loss, because it's part of the antenna feed point.

Getting back to prcguy's first post, last paragraph... Don't use coax if you use an antenna tuner. Use balanced line. Those LDG tuners are little more than an attenuator used to keep the transmitter happy. You could probably do just as well by getting a 6 db 100 watt pad, and hooking it up to a random piece of wire. What doesn't radiate will turn into heat, just like in a coax antenna tuner.
 

KQ4BX

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So nobody thinks that the tuner consumes any power it a poor match? Does a tuner making a 10:1 match get warm?
 
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My primary HF antenna is a flat top doublet about 88 ft end to end fed with about 30 ft of 450 Ohm ladder line to a 4:1 balun mounted on my roof with a 3 ft piece of RG8 to a remote tuner also mounted on the roof, then about 35 ft of RG8x to my operating position. I use this for both Ham and MARS operation, works quite well, I have a dual needle meter in the shack so I can check the match.

This setup fulfills several requirements for a fairly efficient antenna system, a balanced antenna (not dependent on a extensive RF ground, low loss short feed line, ability to provide an acceptable match to the coax run to my operating position. I have 3 different HF radios that I can switch to this antenna.
 

zz0468

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So nobody thinks that the tuner consumes any power it a poor match? Does a tuner making a 10:1 match get warm?
You missed my point entirely.

Does a tuner get warm just by matching a 10:1 match? My point was, the reality is far more complex than your simple question. It can get warmer, but it doesn't have to. Obviously there are losses regardless of the vswr, but a tuner working with a 10:1 mismatch in open wire line will transfer most of the power to the line and antenna. A tuner operating into a 10:1 mismatch into coax will see a substantial amount of rf loss in the coax itself. A tuner operating into a 10:1 mismatch with no place else for the rf to dissipate will absorb the power and turn it into heat.

All of the above and an infinite variety of in-betweens, depending on the specific circumstances.
 

jim202

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If you have an antenna tuner, and your antenna is a 10:1 match for your frequency, and the tuner brings it down to 1.2:1, do you get the same, or close to the same transfer of power to the antenna as you would if the antenna was a true 1.2:1?

I have more to say on this, but I want to see what everyone believes to know about this subject.
Bottom simple line answer here is if the antenna was not tuned to the frequency your trying to use it on, your transmit energy is not being passed into the air very well. The antenna is going to cause the high SWR and not radiate much power like a tuned antenna will.

Using the tuner only makes the transmitter happy that is is seeing a close to matched load as possible. The tuner doesn't make the antenna any better to radiate the power.
 

prcguy

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Yes and no, depends on the antenna. For example, take a 40 or 80m tuned resonant dipole fed with a short run of low loss 50 ohm coax and make some field strength measurements. Then replace the coax with 450 ohm balanced line and a good tuner, which will have about 9:1 mismatch between the antenna and feedline. The field strength will be nearly the same because virtually all the power will be radiated except for a very small amount lost in the tuner and feedline.

Now trim a couple of feet off the same antenna or even add a few feet so its no longer resonant within the ham band and the antenna fed with coax will probably show some degradation in field strength but the antenna fed with low loss balanced line and tuner will radiate about the same.

I'll have to search around for the measurements but a dipole fed with low loss balanced line and a tuner can be cut down to either 60% or 70% of a full size 1/2 wave and only loose about 1dB of efficiency. 1dB would go unnoticed on the air without test equipment to measure it.

Try cutting your RG-58 fed 40 or 80m Hamstick mobile antenna down to resonate outside the ham band with a tuner at the radio and you will see some degradation. So having an antenna tuned to resonance is mandatory with some types of antennas and makes no difference with other types.

Understanding what types of antennas are sensitive to this allows you to choose the best antenna for your situation and get the most out of it. Using a tuner will also allow you to use an antenna that would otherwise cause the radio to fold back power and not work on transmit. If you use low loss balanced line to a dipole type antenna the tuner and feedline loss can almost be ignored, even if the antenna is nowhere near resonance.
prcguy



Bottom simple line answer here is if the antenna was not tuned to the frequency your trying to use it on, your transmit energy is not being passed into the air very well. The antenna is going to cause the high SWR and not radiate much power like a tuned antenna will.

Using the tuner only makes the transmitter happy that is is seeing a close to matched load as possible. The tuner doesn't make the antenna any better to radiate the power.
 

KQ4BX

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It only stands to reason that if there were only one db of difference between resonance and non-resonance when using a tuner ,and all you needed was a tuner to make everything right with the world, who would bother to build a resonant antenna?

Does the match made result in any power being dissipated in the tuner circuit? The general idea that some are giving is that the wire is made to be resonant with the tuner. So is that to say that a shift of some sort happens in the tuner to the signal that then proceeds to the antenna?

The resonant antenna causes my LDG auto tuner to enter bypass. When it is not in bypass, I believe that a portion of the power is absorbed by the tuner because the tuner becomes part of the antenna. Hence the reason that the best place for the tuner is at the antenna. The tuner can balance things out anywhere in the transmit path, but becoming part of the antenna circuit, makes being at the antenna, or as close as possible, a perfect situation. The antenna feed line should already be a match for the radio.

So, if we wanted to test some of this, we could monitor the internal temperature of the tuner as we tune several antennas that progressively get to be a worse match. If the temperature increases with the greater compensation, then the tuner is eating some of that power, and passing what it can to the antenna.

I do know that my tuner goes cold at resonance, and it is not cold when it is actively matching the antenna.

Our goal is to have resonant antennas, then use a tuner to broaden out the resonant parts of the band, making the non-resonant frequencies friendlier to our transmitters. in my mind, a tuner is not to make our antenna happy, it is to make our transmitter happy. The way some describe a tuner, we should be calling it a magic box.
 

prcguy

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As you gain experience with antennas and find a large random length but symmetrical dipole fed with balanced line to a tuner performs very well on multiple bands and in some cases better than a resonant dipole, your goal may not be a resonant antenna any longer.

If you search the web you will find calculations and field measurements from reputable people that have proven a dipole that is 70% or so of a full size 1/2 wave dipole will radiate a signal within 1dB of a full size 1/2 wave dipole when fed with balanced line to a tuner. You will not get the same results with a coax fed dipole and tuner.

Tuners will have loss and I think the best way to find out is to measure the input power to the tuner then the RF voltage and current at the output and see how much power remains, which will vary with tuner mfr and load. You can also take field strength measurements of a tuned 1/2 wave dipole fed with coax, then swap the coax for balanced line and a tuner, then shorten the antenna to 70% and compare results.
prcguy

It only stands to reason that if there were only one db of difference between resonance and non-resonance when using a tuner ,and all you needed was a tuner to make everything right with the world, who would bother to build a resonant antenna?

Does the match made result in any power being dissipated in the tuner circuit? The general idea that some are giving is that the wire is made to be resonant with the tuner. So is that to say that a shift of some sort happens in the tuner to the signal that then proceeds to the antenna?

The resonant antenna causes my LDG auto tuner to enter bypass. When it is not in bypass, I believe that a portion of the power is absorbed by the tuner because the tuner becomes part of the antenna. Hence the reason that the best place for the tuner is at the antenna. The tuner can balance things out anywhere in the transmit path, but becoming part of the antenna circuit, makes being at the antenna, or as close as possible, a perfect situation. The antenna feed line should already be a match for the radio.

So, if we wanted to test some of this, we could monitor the internal temperature of the tuner as we tune several antennas that progressively get to be a worse match. If the temperature increases with the greater compensation, then the tuner is eating some of that power, and passing what it can to the antenna.

I do know that my tuner goes cold at resonance, and it is not cold when it is actively matching the antenna.

Our goal is to have resonant antennas, then use a tuner to broaden out the resonant parts of the band, making the non-resonant frequencies friendlier to our transmitters. in my mind, a tuner is not to make our antenna happy, it is to make our transmitter happy. The way some describe a tuner, we should be calling it a magic box.
 
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