Antenna tuning or matching unit

[Elecraft mailing list]

This all depends on what is meant by antenna tuning.
When teaching newbies the wrong phrase can cause problems that are not seen till later.
Antennas are tuned with wire cutters or a hacksaw so the feed impedance is the desired value, ideally 50 ohm resistive or at least a match for the feeder concerned.
Of course that is not always practical so an antenna matching unit brings the antenna or antenna plus feeder input impedance to the value wanted by the transmitter.
Too often I have seen students believe the ATU alters the current and voltage distribution on the antenna so it looks exactly like the distribution on a dipole of the correct length for the frequency concerned.
Granted the currents and voltages might change as the ATU is adjusted but that does not make the antenna radiate more efficiently. The reflection at the feeder/antenna junction is unchanged.
In training we use the term antenna matching unit, AMU, to avoid best we can the students starting off with the wrong impression.
Amongst ourselves we can get away with slack terminology, we all know what is meant; in front of trainees it is a different story.
73 Alan  G0HIQ


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[Don Wilhelm]

On this subject, it may be of interest to point to the article on my
website www.w3fpr.com "Antennas, Transmission Lines and Tuners".  This
article first appeared in QRP Quarterly in July 2001.

I am pleased that DXzone has also recognized that article and has
included it in its Antennas/Theory category - see
https://www.dxzone.com/dx19232/antennas-and-transmission-lines-myths.html

There is not much math in the article, but you may find the concepts
valuable.  The sections on "SWR as a friend" and "Antenna Tuners" is
particularly relevant to the current topic.

73,
Don W3FPR

On 2/20/2018 8:16 PM, Alan B via Elecraft wrote:
> This all depends on what is meant by antenna tuning.
> When teaching newbies the wrong phrase can cause problems that are not seen till later.
> Antennas are tuned with wire cutters or a hacksaw so the feed impedance is the desired value, ideally 50 ohm resistive or at least a match for the feeder concerned.
> Of course that is not always practical so an antenna matching unit brings the antenna or antenna plus feeder input impedance to the value wanted by the transmitter.
> Too often I have seen students believe the ATU alters the current and voltage distribution on the antenna so it looks exactly like the distribution on a dipole of the correct length for the frequency concerned.
> Granted the currents and voltages might change as the ATU is adjusted but that does not make the antenna radiate more efficiently. The reflection at the feeder/antenna junction is unchanged.
> In training we use the term antenna matching unit, AMU, to avoid best we can the students starting off with the wrong impression.
> Amongst ourselves we can get away with slack terminology, we all know what is meant; in front of trainees it is a different story.
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[Bill K9YEQ]

Don, thank you for the reference.  I know I read this back when you wrote it.  I have saved as a reference for other operators, who seem to need a bit more understanding.

73,
Bill
K9YEQ

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of Don Wilhelm
Sent: Tuesday, February 20, 2018 8:10 PM
To: [hidden email]
Subject: Re: [Elecraft] Antenna tuning or matching unit

On this subject, it may be of interest to point to the article on my website www.w3fpr.com "Antennas, Transmission Lines and Tuners".  This article first appeared in QRP Quarterly in July 2001.

I am pleased that DXzone has also recognized that article and has included it in its Antennas/Theory category - see https://www.dxzone.com/dx19232/antennas-and-transmission-lines-myths.html

There is not much math in the article, but you may find the concepts valuable.  The sections on "SWR as a friend" and "Antenna Tuners" is particularly relevant to the current topic.

73,
Don W3FPR

On 2/20/2018 8:16 PM, Alan B via Elecraft wrote:
> This all depends on what is meant by antenna tuning.
> When teaching newbies the wrong phrase can cause problems that are not seen till later.
> Antennas are tuned with wire cutters or a hacksaw so the feed impedance is the desired value, ideally 50 ohm resistive or at least a match for the feeder concerned.
> Of course that is not always practical so an antenna matching unit brings the antenna or antenna plus feeder input impedance to the value wanted by the transmitter.
> Too often I have seen students believe the ATU alters the current and voltage distribution on the antenna so it looks exactly like the distribution on a dipole of the correct length for the frequency concerned.
> Granted the currents and voltages might change as the ATU is adjusted but that does not make the antenna radiate more efficiently. The reflection at the feeder/antenna junction is unchanged.
> In training we use the term antenna matching unit, AMU, to avoid best we can the students starting off with the wrong impression.
> Amongst ourselves we can get away with slack terminology, we all know what is meant; in front of trainees it is a different story.
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[Bill K9YEQ]

Then there are those of us who use high ratio end fed half waves for specific frequencies with great luck.  I do this on 160 for 1.900 coverage.  This allows me to deviate marginally from that frequency with a matching unit.  Works great near 3.8 as well.  Now to get it further into the trees. Winter has hindered my latest experimental antenna.  NVIS is better than nothing :-).

73,
Bill
K9YEQ

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of Ron D'Eau Claire
Sent: Tuesday, February 20, 2018 9:36 PM
To: [hidden email]
Subject: Re: [Elecraft] Antenna tuning or matching unit

Alan your explanation opens the door to erroneous conclusions. Frequently a feed line does NOT have a low SWR by design. It is still a feed line in that it carries RF from the transmitter site to the radiator with a minimum of radiation from itself. A classic example is the Zepp antenna: a 1/2 wave long radiator fed at one end with a 1/4 wavelength long open wire feed line.
The SWR on the feed line is intentionally very high because its function is to translate the very high impedance at the end of the radiator to a low impedance easily handled by the transmitter, nowadays generally using a matching network commonly called a "tuning unit" since modern transmitters are designed for a 50 ohm non-reactive load.

Another example is a wire radiator fed at the center with open wire feed line for operation on a variety of bands. Again the SWR in the feed line will be very high, depending upon the length of the radiator, the length of the feed line and the frequency of operation. But, using a feed line with an impedance of 450 to 600 ohms, the SWR in a real-world H.F. installation where the radiator is at least 1/2 wavelength long at the lowest frequency of operation, the SWR on the open wire feed line will not exceed about 20:1 so the losses will be very low. The real advantage to this setup is that the matching network can be in the shack and within easy reach of the operator instead of being mounted remotely at the center of the radiator.

I present the use of 50 ohm coaxial line without a matching network as a "special case" where it possible to design a radiator or system of radiators that presents an impedance at its feed point that is a close enough match to
50 ohms without the network. However, using a low-impedance like such as the common coax means we must pay special attention to the SWR on the feed line to avoid excessive losses. For example, with 50 ohm coax in an HF installation, it is easy to realize an SWR of greater than 100:1 and very high losses. In such a case a matching network at the transmitter will not
reduce the feed line losses.  

73, Ron AC7AC


On 2/20/2018 8:16 PM, Alan B via Elecraft wrote:
> This all depends on what is meant by antenna tuning.
> When teaching newbies the wrong phrase can cause problems that are not
seen till later.
> Antennas are tuned with wire cutters or a hacksaw so the feed
> impedance is
the desired value, ideally 50 ohm resistive or at least a match for the feeder concerned.
> Of course that is not always practical so an antenna matching unit
> brings
the antenna or antenna plus feeder input impedance to the value wanted by the transmitter.
> Too often I have seen students believe the ATU alters the current and
voltage distribution on the antenna so it looks exactly like the distribution on a dipole of the correct length for the frequency concerned.
> Granted the currents and voltages might change as the ATU is adjusted
> but
that does not make the antenna radiate more efficiently. The reflection at the feeder/antenna junction is unchanged.
> In training we use the term antenna matching unit, AMU, to avoid best
> we
can the students starting off with the wrong impression.
> Amongst ourselves we can get away with slack terminology, we all know
> what
is meant; in front of trainees it is a different story.

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[Bob McGraw - K4TAX]

I agree with Ron in that one must understand using an ATU at the transmitter does not change feedline loss. In fact it adds additional system loss due to loss incurred in the tuner.  If the transmitter can not deliver rated power into the load that is a different issue to resolve.  The ATU may accomplish this, but with added system loss.

Bob, K4TAX


Sent from my iPhone

> On Feb 20, 2018, at 9:35 PM, Ron D'Eau Claire <[hidden email]> wrote:
>
> Alan your explanation opens the door to erroneous conclusions. Frequently a
> feed line does NOT have a low SWR by design. It is still a feed line in that
> it carries RF from the transmitter site to the radiator with a minimum of
> radiation from itself. A classic example is the Zepp antenna: a 1/2 wave
> long radiator fed at one end with a 1/4 wavelength long open wire feed line.
> The SWR on the feed line is intentionally very high because its function is
> to translate the very high impedance at the end of the radiator to a low
> impedance easily handled by the transmitter, nowadays generally using a
> matching network commonly called a "tuning unit" since modern transmitters
> are designed for a 50 ohm non-reactive load.
>
> Another example is a wire radiator fed at the center with open wire feed
> line for operation on a variety of bands. Again the SWR in the feed line
> will be very high, depending upon the length of the radiator, the length of
> the feed line and the frequency of operation. But, using a feed line with an
> impedance of 450 to 600 ohms, the SWR in a real-world H.F. installation
> where the radiator is at least 1/2 wavelength long at the lowest frequency
> of operation, the SWR on the open wire feed line will not exceed about 20:1
> so the losses will be very low. The real advantage to this setup is that the
> matching network can be in the shack and within easy reach of the operator
> instead of being mounted remotely at the center of the radiator.
>
> I present the use of 50 ohm coaxial line without a matching network as a
> "special case" where it possible to design a radiator or system of radiators
> that presents an impedance at its feed point that is a close enough match to
> 50 ohms without the network. However, using a low-impedance like such as the
> common coax means we must pay special attention to the SWR on the feed line
> to avoid excessive losses. For example, with 50 ohm coax in an HF
> installation, it is easy to realize an SWR of greater than 100:1 and very
> high losses. In such a case a matching network at the transmitter will not
> reduce the feed line losses.  
>
> 73, Ron AC7AC
>
>
>> On 2/20/2018 8:16 PM, Alan B via Elecraft wrote:
>> This all depends on what is meant by antenna tuning.
>> When teaching newbies the wrong phrase can cause problems that are not
> seen till later.
>> Antennas are tuned with wire cutters or a hacksaw so the feed impedance is
> the desired value, ideally 50 ohm resistive or at least a match for the
> feeder concerned.
>> Of course that is not always practical so an antenna matching unit brings
> the antenna or antenna plus feeder input impedance to the value wanted by
> the transmitter.
>> Too often I have seen students believe the ATU alters the current and
> voltage distribution on the antenna so it looks exactly like the
> distribution on a dipole of the correct length for the frequency concerned.
>> Granted the currents and voltages might change as the ATU is adjusted but
> that does not make the antenna radiate more efficiently. The reflection at
> the feeder/antenna junction is unchanged.
>> In training we use the term antenna matching unit, AMU, to avoid best we
> can the students starting off with the wrong impression.
>> Amongst ourselves we can get away with slack terminology, we all know what
> is meant; in front of trainees it is a different story.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>

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[David Gilbert]

Most of that is accurate, but this part is misleading:

"Antennas are tuned with wire cutters or a hacksaw so the feed impedance
is the desired value, ideally 50 ohm resistive or at least a match for
the feeder concerned."

I think we're getting a bit off track by lumping "tuning" and "matching"
together as if they are the same effects.  They are not. At least in my
world, tuning refers to compensating for reactance at the feedpoint by
some means that nets it out to zero.  In that respect, doing so with a
network at the other end of the feedline accomplishes the exact same
thing as using wire cutters or a hacksaw on the antenna itself.  They
are not different.     As you say, the current and voltage distributions
are not the same as if you cut the antenna to length, but the lack of
feedpoint reactance is.

Matching the feedpoint impedance to the feedline, or compensating the
effects of the mismatch at the transmitter end, is an entirely different
matter and there is no requirement that "tuning" per se accomplishes a
match at either end ... only that it bring the reactance at the antenna
to zero.  We do, of course, also want our "antenna tuner" to give us the
proper match, and in common practice that's what it does.  In that
regard, calling it an "antenna tuner" only tells part of the story and
"antenna coupler" might be a more rigorous term ... more rigorous even
than "antenna matching unit."

73,
Dave   AB7E



On 2/20/2018 6:16 PM, Alan B via Elecraft wrote:

> This all depends on what is meant by antenna tuning.
> When teaching newbies the wrong phrase can cause problems that are not seen till later.
> Antennas are tuned with wire cutters or a hacksaw so the feed impedance is the desired value, ideally 50 ohm resistive or at least a match for the feeder concerned.
> Of course that is not always practical so an antenna matching unit brings the antenna or antenna plus feeder input impedance to the value wanted by the transmitter.
> Too often I have seen students believe the ATU alters the current and voltage distribution on the antenna so it looks exactly like the distribution on a dipole of the correct length for the frequency concerned.
> Granted the currents and voltages might change as the ATU is adjusted but that does not make the antenna radiate more efficiently. The reflection at the feeder/antenna junction is unchanged.
> In training we use the term antenna matching unit, AMU, to avoid best we can the students starting off with the wrong impression.
> Amongst ourselves we can get away with slack terminology, we all know what is meant; in front of trainees it is a different story.
> 73 Alan  G0HIQ
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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[Jim Brown-10]

On 2/20/2018 9:35 PM, David Gilbert wrote:
> "Antennas are tuned with wire cutters or a hacksaw so the feed
> impedance is the desired value, ideally 50 ohm resistive or at least a
> match for the feeder concerned."
>
> I think we're getting a bit off track by lumping "tuning" and
> "matching" together as if they are the same effects.  They are not.

Yep.  And many antennas are better matched to other than 50 ohm
feedlines. My high dipoles are in the range of 85-90 ohms, so I use a
good RG11 to feed them. And those dipoles are for 80 and 40M, so their
lengths are tweaked so that, with stub matching in the shack, the Z
presented to the 87A (tube) power amps is within the range they are
happy feeding.

> At least in my world, tuning refers to compensating for reactance at
> the feedpoint by some means that nets it out to zero.  In that
> respect, doing so with a network at the other end of the feedline
> accomplishes the exact same thing as using wire cutters or a hacksaw
> on the antenna itself.

Don't agree with that -- the match between the antenna and the feedline
determines the loss in the feedline. The tuning network between the
transmitter and the feedline does NOT change the loss in the feedline,
it simply gives the transmitter a load that it's happy driving, and to
which it can deliver maximum power.  AND -- we are NOT matching the
antenna Z to the TX output Z -- for most real transmitters, their output
Z is LESS than the load they are designed to drive, and that output Z
changes dynamically with signal level! Back in the olden days, we young
EEs learned about how do determine this with "load lines."

> They are not different.     As you say, the current and voltage
> distributions are not the same as if you cut the antenna to length,
> but the lack of feedpoint reactance is.

But with most antennas, zero feedpoint reactance can be achieved at only
one frequency -- it takes something like a SteppIR to move that zero
point around the band. I may resonate my 80M dipole at 3625, but I
almost never operate there. Rather, I'm mostly between 3500 and 3600,
and between 3650 and 3850.

And then there are directional antennas like Yagis. :)

73, Jim K9YC

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[David Gilbert]

Agree with all of that.  I realized after I wrote it that I should have
stressed that zeroing out the reactance at the antenna from the shack
end of the feedline does NOT match it at the the feedpoint and that
you'd still have SWR losses in the feedline and also in the matching
network.  I was referring only to the reactance and should have made
that more clear.

Also agree about the output impedance of the transmitter, but I was
trying to simplify the discussion and didn't want to make it more
obscure than it had already become.

73,
Dave   AB7E



On 2/20/2018 11:51 PM, Jim Brown wrote:

> On 2/20/2018 9:35 PM, David Gilbert wrote:
>> "Antennas are tuned with wire cutters or a hacksaw so the feed
>> impedance is the desired value, ideally 50 ohm resistive or at least
>> a match for the feeder concerned."
>>
>> I think we're getting a bit off track by lumping "tuning" and
>> "matching" together as if they are the same effects.  They are not.
>
> Yep.  And many antennas are better matched to other than 50 ohm
> feedlines. My high dipoles are in the range of 85-90 ohms, so I use a
> good RG11 to feed them. And those dipoles are for 80 and 40M, so their
> lengths are tweaked so that, with stub matching in the shack, the Z
> presented to the 87A (tube) power amps is within the range they are
> happy feeding.
>
>> At least in my world, tuning refers to compensating for reactance at
>> the feedpoint by some means that nets it out to zero.  In that
>> respect, doing so with a network at the other end of the feedline
>> accomplishes the exact same thing as using wire cutters or a hacksaw
>> on the antenna itself.
>
> Don't agree with that -- the match between the antenna and the
> feedline determines the loss in the feedline. The tuning network
> between the transmitter and the feedline does NOT change the loss in
> the feedline, it simply gives the transmitter a load that it's happy
> driving, and to which it can deliver maximum power.  AND -- we are NOT
> matching the antenna Z to the TX output Z -- for most real
> transmitters, their output Z is LESS than the load they are designed
> to drive, and that output Z changes dynamically with signal level!
> Back in the olden days, we young EEs learned about how do determine
> this with "load lines."
>
>> They are not different.     As you say, the current and voltage
>> distributions are not the same as if you cut the antenna to length,
>> but the lack of feedpoint reactance is.
>
> But with most antennas, zero feedpoint reactance can be achieved at
> only one frequency -- it takes something like a SteppIR to move that
> zero point around the band. I may resonate my 80M dipole at 3625, but
> I almost never operate there. Rather, I'm mostly between 3500 and
> 3600, and between 3650 and 3850.
>
> And then there are directional antennas like Yagis. :)
>
> 73, Jim K9YC
>
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