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Antenna tuners: Where is best and why?

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#1
Hi all,

Could someone explain why one would want to tune an antenna as close to the feed point as possible? Most antenna tuners are located inside the shack near the radio, but some tuners that are sold are meant to be mounted outdoors close to the feed point. What is the advantage of the outdoor tuners?

Thanks.
 
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#2
Hi all,



Could someone explain why one would want to tune an antenna as close to the feed point as possible? Most antenna tuners are located inside the shack near the radio, but some tuners that are sold are meant to be mounted outdoors close to the feed point. What is the advantage of the outdoor tuners?



Thanks.


If you use a antenna tuner next to the transmitter, you are only correcting the reflected power from the tuner to the radio. The power from the tuner to the Antenna will not be the best transferred.

You want the most efficient antenna possible to transfer your transmit power as well as possible.

Put a good tuner at the Antenna feed point and you have the best of both worlds,


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W9BU

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#3
Antenna matching units, aka "tuners", are often installed near the transmitter because it's convenient for adjustments and monitoring. But, from the tuner to the antenna will still have a high SWR and, if you are using coax for feedline between the tuner and the antenna, there will be considerable loss in that coax.

OTOH, if you put the tuner at the antenna feed point, you can run coax from the transmitter to the tuner confident that the remote tuner will adjust your antenna feed point impedance so that the coax between the transmitter and the tuner sees a 1:1 match, thus, minimizing the loss.
 
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#4
Yes and yes. If you look up the advertised loss for any particular coax it will be under a perfect matched condition with a 50 ohm source and 50 ohm load. If you measure a length of coax under these conditions it may have a fraction of a dB of loss at HF frequencies but into a 10:1 or worse match like you will encounter with a G5RV or many other antennas, the feedline loss can now be 6dB or more for the same coax that had a fraction of a dB loss otherwise.

For some antennas its very important to put the tuner or coupler right at the antenna like a non resonant 43ft vertical over a ground plane. If you simply connect 100ft of coax to the same antenna and use a tuner in the shack it might provide a good match to the radio but you could loose 75% or more of the signal you send and receive on the 43ft vertical.

A tuner at the radio is generally referred to as a "line flattener" and intended to fix minor VSWR fluctuations, or to allow operation over a slightly wider frequency range of a resonant antenna. Even though these line flatteners like a typical LDG tuner will tune up to 10:1, its not good to operate under those conditions with long runs of coax.

A tuner or coupler intended to be right at the antenna feedpoint is a little different animal than a typical LDG and couplers made by SGC or the Icom AH-4 and similar cover a very wide range and are intended to tune a whip or dipole over the entire HF range without any problems. In these tuners or couplers you will find components like capacitors rated for 5kV or more to handle extreme voltages with some antennas.

If you look at components in an LDG tuner they come nowhere near the ratings of tuners intended to tune whips or random wires that might end up a resonant 1/2 wavelength and can reach several thousand volts at the feedpoint even with only 100W.
prcguy

Antenna matching units, aka "tuners", are often installed near the transmitter because it's convenient for adjustments and monitoring. But, from the tuner to the antenna will still have a high SWR and, if you are using coax for feedline between the tuner and the antenna, there will be considerable loss in that coax.

OTOH, if you put the tuner at the antenna feed point, you can run coax from the transmitter to the tuner confident that the remote tuner will adjust your antenna feed point impedance so that the coax between the transmitter and the tuner sees a 1:1 match, thus, minimizing the loss.
 
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#5
Thank you guys for the explanation. They were very clear and very helpful. I'm going out on a limb here and saying that this isn't that bad of a problem for me since my antennas are resonant or nearly resonant over the parts of the bands where I operate.
 
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#8
Why would a transmitter designed to deliver full power into a 50 ohm load need to tune a 50 ohm coax?


The 50 ohm coax delivers max power when matched loads and sources are present.

If you use 300 or 450 twin line, the Antenna would need to be designed for 300 or 450 ohms. Prior TV reception antennas were. In order to use shielded 75 ohm coax, you needed 3 to 1 baluns at the Antenna for optimum energy transfer.

That is why I prefer using SGC autotuner s mounted at the Antenna. They quickly tune the Antenna and feedline.


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Ed_Seedhouse

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#9
That is why I prefer using SGC autotuner s mounted at the Antenna. They quickly tune the Antenna and feedline.
So does a tuner at the receiver end if the transmission line is lossless and the SWR is close to 1:1. Of course in the real world no transmission line is lossless, but the question is does it matter in practise? And the answer is that it generally doesn't, very much. As long as it's tuned to close enough to 1:1, the tuner will cause the line to deliver all it's power from the transmitter into the antenna, minus losses radiated as heat, no matter where in the transmission line the tuner is.

See the article here: http://w5dxp.com/OWT1.htm

Warning: contains mathematics.
 
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#10
I think Ed_Seedhouse answered my question with the article he cited, but I will ask it anyway. In the marketplace, why do "at the radio" tuners vastly outnumber "at the antenna" tuners? On the Universal Radio site, I count only 3 or 4 remote tuners whereas all the rest are indoor tuners.
 
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#11
Because most people are too dumb to realize that a low SWR reading at the radio doesn't tell the whole story of what is happening with the antenna and coax.
 
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#12
In earlier times amateurs used more balanced feedlines like 450 or 600 ohm ladder line, 300 ohm TV twinlead, etc. In these cases a balanced feedline all the way to a tuner near the radio was not a problem because the balanced line has very low loss and it doesn't matter if you have a 10:1 or worse VSWR between the antenna, feedline and radio, everything just works and works well.

Balanced tuners were also more common and a lot of amateurs used the classic 135ft dipole fed with balanced line, or end fed Zepp antennas fed with balanced line and so on. Antennas like these don't even have to be resonant to radiate well and you can run many if not all HF bands with one antenna fed with balanced line to a balanced tuner with virtually no loss.

Unfortunately balanced line takes some special care getting it from the antenna into the shack and away from any metal, so coax has become the preferred feedline over the years. With coax you loose the ability to run multiband with a simple dipole and have to be aware of high VSWR and associated coax losses. But it is convenient and doesn't change properties in the rain and it works fine for feeding many types of antennas if you don't operate things beyond their limits. And that comes back around to using a tuner at the radio to fix problems downstream where coax is being pushed beyond where it should be used.
prcguy
 

popnokick

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#13
Isn't it true that placing the tuner at the antenna end of the coax will be more expensive... if only for the additional cost of purchasing / installing the tuner control & power cables? Many of the hams I know, when faced with a decision of "What's best technically?" versus "What is cheaper?" will ALWAYS chose to save the buck. There seems to be some universality to this. If not, how could you get away with naming your Amateur Radio business "Cheapham.com"? There are the "Spend whatever it takes to get it right" hams, but my experience is they are far fewer in number. Nirvana is "technically the best, and lowest cost". The two seldom go together. In Information Technology we have a saying for persons considering purchase / upgrade of technology: "Fast. Cheap. Good. You get to pick two of the three."
 

Ed_Seedhouse

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#14
Isn't it true that placing the tuner at the antenna end of the coax will be more expensive... if only for the additional cost of purchasing / installing the tuner control & power cables? Many of the hams I know, when faced with a decision of "What's best technically?" versus "What is cheaper?" will ALWAYS chose to save the buck. There seems to be some universality to this.
You also don't have to make sure your auto-tuner is weatherproofed if it's by your rig, and you can see visually how well it's tuned. A tuner at either end of a lossless transmission line will perform identically. In practice no transmission line is lossless but so long as the losses are reasonable there is little or no practical performance difference.

A coax doesn't magically make a multi-band antenna into a single band antenna and all real world antennas are compromises. I have a dipole at a height 15 feet half outside and half inside, long enough to be close to a half wave at 40 meters. With the auto-tuner I have contacts on several bands including 80 meters. I can tune to 1:1 on 80 but the antenna is obviously going to be inefficient there due to it's short length. Well, I have friends who've made contacts while using a light bulb as a dummy load, or so they tell me.

If I had enough money I would choose a tuner at the antenna end, but I don't. Hell if I had enough money I'd have a kilowatt rig and 160 meter loop at a distant location where the RF noise was low (it's usually S7 at my house) and run it remotely from my living room. Never going to happen, though.
 
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#15
Yes, a typical 100W indoor tuner (line flattener) like an LDG Z-100 series might run you $160. A similar tuner in a weather proof box (LDG RT-100) to place at your antenna might run you $230. An Icom AH-4 remote whip/wire tuner runs about $270, so the remote units do cost more. Some remote tuners designed for wires and whips cover a much larger tuning range than one for indoor use driving coax.

But there are things an RT-100 or AH-4 remote tuner can do that a Z-100 tuner at your radio feeding 100ft of RG-8X coax cannot do and that's get all your power into the antenna and provide a good match between your long feedline and radio. There is a tuner made for every place in your antenna system, choose wisely and you make the most of your transmit and receive signals. Skimp or make the wrong choice and your signal suffers or you can't use your antenna on some bands.

And its not really a choice of fast, cheap or good, you can have a really good antenna/feedline system for very cheap if you do some homework and make good decisions. One might be to consider a multiband ZS6BKW dipole antenna over its nearly identical G5RV cousin. Why? Because a G5RV has a terrible match on most bands and if you feed it with 100ft of cheap coax you will loose a lot of signal on many bands due to high coax attenuation. The more modern designed ZS6BKW has a good match on most bands and under the same long coax conditions it will get noticeably more signal on the air and may not require a tuner at all. That is a win-win with good performance and saving the cost of a tuner for some.
prcguy

Isn't it true that placing the tuner at the antenna end of the coax will be more expensive... if only for the additional cost of purchasing / installing the tuner control & power cables? Many of the hams I know, when faced with a decision of "What's best technically?" versus "What is cheaper?" will ALWAYS chose to save the buck. There seems to be some universality to this. If not, how could you get away with naming your Amateur Radio business "Cheapham.com"? There are the "Spend whatever it takes to get it right" hams, but my experience is they are far fewer in number. Nirvana is "technically the best, and lowest cost". The two seldom go together. In Information Technology we have a saying for persons considering purchase / upgrade of technology: "Fast. Cheap. Good. You get to pick two of the three."
 
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popnokick

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#16
Agree with last post by prcguy... and the ZS6BKW is one of those "technically best / good, low cost" solutions. Like the Windom Off-Center Dipole.... which can be used without a tuner on most bands, fed with coax all the way up to the balun, no minimum suspended feed line length, and without concerns about feed line proximity to large metal surfaces.
 

Ed_Seedhouse

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But there are things an RT-100 or AH-4 remote tuner can do that a Z-100 tuner at your radio feeding 100ft of RG-8X coax cannot do and that's get all your power into the antenna and provide a good match between your long feed-line and radio.
No it can't. There is always loss in any transmission line and putting the tuner at the other end won't make the loss go away, even if your understanding of what a tuner does were correct that would just put the loss before the tuner instead of after it. The most a tuner at the antenna lend would do is to deliver all the power it received over there at the other end of the lossy transmission line into the antenna, less the internal losses in the tuner itself. That's if your understanding of how a tuner works is right. According to the link I provided it isn't correct.

Did you read the link I gave? http://w5dxp.com/OWT1.htm

Just so you see the final conclusion it is

"The following conclusion seems obvious:

The main purpose of an antenna tuner is to cause the maximum amount of current to flow through the radiation resistance at the antenna resulting in PRad=I2(RRad) watts of power being radiated at the antenna."

Can you show us all where the error in his mathematics is?

To put it another way what a tuner effectively does is act as a "transmitter" with the correct impedance to deliver power into the transmission line/antenna system.
 
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No it can't. There is always loss in any transmission line and putting the tuner at the other end won't make the loss go away, even if your understanding of what a tuner does were correct that would just put the loss before the tuner instead of after it. The most a tuner at the antenna lend would do is to deliver all the power it received over there at the other end of the lossy transmission line into the antenna, less the internal losses in the tuner itself. That's if your understanding of how a tuner works is right. According to the link I provided it isn't correct.

Did you read the link I gave? http://w5dxp.com/OWT1.htm

Just so you see the final conclusion it is

"The following conclusion seems obvious:

The main purpose of an antenna tuner is to cause the maximum amount of current to flow through the radiation resistance at the antenna resulting in PRad=I2(RRad) watts of power being radiated at the antenna."

Can you show us all where the error in his mathematics is?

To put it another way what a tuner effectively does is act as a "transmitter" with the correct impedance to deliver power into the transmission line/antenna system.


Nobody says there isn't any loss. You can minimize the losses by optimization of power transfer between remote tuner and your radio transceiver.

Your remark about the error in mathematics is however uncalled for. If you think the math is valid, fine. Do remember that even a genius like Albert Einstein divided by zero and screwed up one of the theories of relativity.

Do leave the condeconding remarks somewhere else not on this forum.


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#19
Yes there is always coax loss but I'm referring to additional loss beyond advertised loss due to operating the coax under high VSWR. If a length of coax has 1dB loss under matched conditions and your feed line to antenna VSWR is 20:1 you can have some serious additional coax loss because of that.

Put a tuner between the antenna and feedline and you eliminate the additional coax loss due to high VSWR and still have the 1dB loss you started with. Plus some loss in the tuner of course and that's a whole other topic with many variables.

And no I didn't see your link and I didn't offer any math so how can it be incorrect?
prcguy

No it can't. There is always loss in any transmission line and putting the tuner at the other end won't make the loss go away, even if your understanding of what a tuner does were correct that would just put the loss before the tuner instead of after it. The most a tuner at the antenna lend would do is to deliver all the power it received over there at the other end of the lossy transmission line into the antenna, less the internal losses in the tuner itself. That's if your understanding of how a tuner works is right. According to the link I provided it isn't correct.

Did you read the link I gave? http://w5dxp.com/OWT1.htm

Just so you see the final conclusion it is

"The following conclusion seems obvious:

The main purpose of an antenna tuner is to cause the maximum amount of current to flow through the radiation resistance at the antenna resulting in PRad=I2(RRad) watts of power being radiated at the antenna."

Can you show us all where the error in his mathematics is?

To put it another way what a tuner effectively does is act as a "transmitter" with the correct impedance to deliver power into the transmission line/antenna system.
 

Ed_Seedhouse

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#20
Your remark about the error in mathematics is however uncalled for. If you think the math is valid, fine. Do remember that even a genius like Albert Einstein divided by zero and screwed up one of the theories of relativity.

Do leave the condeconding remarks somewhere else not on this forum.
If one doesn't understand the math then it seems to me that deciding that it *therefore* must be wrong is pretty condescending in and of itself.

"Einstein made a mistake therefore some other completely unrelated bit of mathematics must be wrong" doesn't sound like a sensible argument to me. If you find that condescending then you feel what you feel. I am not going to agree that you are right just because it might ameliorate your feelings. Sorry.
 
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