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Re: [TowerTalk] 75ohm cable

To: "" <>
Subject: Re: [TowerTalk] 75ohm cable
From: "Jim Brown" <>
Date: Mon, 19 Jul 2010 18:14:34 -0700
List-post: <">>
>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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