Here, here. Too much time splitting hairs when it comes to SWR. The ham on
the other end probably doesn't even hear the diff between a low and
relatively low or moderately high SWR.
Don W7WLL
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <Towertalk@contesting.com>
Sent: Monday, July 19, 2010 6:14 PM
Subject: Re: [TowerTalk] 75ohm cable
>You can have up to a 2:1 mismatch (SWR) at the transmitter using 75 ohm
>line
>if the antenna is a flat 50 ohms. If your 75 ohm line happens to be a
>multiple of a quarter wave length that will transform the 50 ohm load to
>100
>ohms seen at the transmitter end.
So what? Any rig with an antenna tuner, including tube power amps, will
drive
that just fine. Loss in the line due to mismatch depends ONLY on the
mismatch
between the antenna and the line. The worst that can get with a 2:1 mismatch
is a few tenths of a dB.
There is NO loss created by a mismatch between the TX and the line -- all we
need to do is make the output stage happy, and an antenna tuner does that
just fine. Remember that ALL of the matching methods for use at the antenna
being suggested are very frequency sensitive -- they will work only on one
band, and not necessarily over a relatively wide band. It is FAR more
flexible to use a tuner in the shack than to worry about the small mismatch
at the antenna.
FAR too much time is spent in the wringing of hands over a relatively small
mismatch. If the output stage is happy, be happy.
73, Jim Brown K9YC
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