[Top] [All Lists]

[TowerTalk] Antenna Tuners

To: <>
Subject: [TowerTalk] Antenna Tuners
From: (T. A. Russell)
Date: Sun, 09 Mar 1997 23:33:06 EST
Bill - 

The answers to your questions are YES and YES...

BUT, before you get too concerned, you need to look at the alternatives
and calculate the losses.

It's not very practical to place an antenna tuner at the antenna unless
you have some way of remotely tuning it. 

Commercial practice is to put the tuner at the transmitter if the SWR
is under 3:1 at the antenna.  The additional losses due to SWR are
quite small with an SWR of 3:1 or less at the antenna.

The ARRL antenna books (older ones anyway) had a set of curves of
additional loss due to mismatch as a function of SWR and lineloss
of the cable (when properly matched).  (Or, check the HANDBOOKS)

Most of the energy is radiated by the antenna but some amount is
reflected back to the transmitter/tuner which will NOT look like 50 
Ohms to the reflected wave (since there was an SWR and the tuner was
adjusted to provide a match between this impedance and the 50 ohm
transmitter output) SO, there will be a reflection at the tuner
back to the antenna where most of the energy will be radiated and
a smaller amount will again be reflected back to the tuner, etc, etc.
This process will go back and forth (at the speed of light) until all of
the power is either radiated from the antenna or dissipated as heat
in the transmission line.  The lower the SWR at the antenna and the
lower the loss in the line, the less the power lost as heat in the line.

For many years, I have tuned my 80M dipoles to CW and use a tuner
on SSB with a 5:1 SWR at 3.8 MHz.  Using 500 ft of 3/4 inch CATV
hardline to feed this antenna, the additional loss due to SWR is 
less than 1 dB. (I don't have the curves here at the computer.)
These antennas have worked a LOT of difficult DX on 75M SSB!

de Tom - N4KG

On Sun, 9 Mar 1997 21:12:01 -0600 (Hawkins, Bill)
>Hi Yall
>A recent posting reminded me that I have had a question for
>a long time which I have never asked. So here it is.
>Suppose I put up an antenna, generally the best I can afford.
>I feed it the best way I know how. 
>I hook it to my antenna tuner to which I hook my rig (oldtimers
>talk for transceiver).
>I tune the tuner so the rig shows a perfect match and happily talk 
>Here's the question.
>Unless (a BIG unless) the feedline is a perfect match for the 
>antenna, ain't I just fooling the rig and matching it to the feedline
>while the feedline is still probably mismatched to the antenna
>and bouncing reflected power all around?
>Another question.
>Unless everything is properly matched (a BIG unless),
>Shouldn't the antenna tuner be at the antenna and the 
>feedline tuner be at the rig?
>Any words of wisdom?
>Bill W5EC
>FAQ on WWW:     
>Administrative requests:
>Sponsored by:             Akorn Access, Inc. & N4VJ / K4AAA

FAQ on WWW:     
Administrative requests:
Sponsored by:             Akorn Access, Inc. & N4VJ / K4AAA

<Prev in Thread] Current Thread [Next in Thread>