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[TowerTalk] 75 ohm feedline

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Subject: [TowerTalk] 75 ohm feedline
From: (Pete Smith)
Date: Sun, 06 Jul 1997 21:20:27
At 12:23 PM 7/4/97 -0400, Bob Locher wrote:
>I don't understand the reluctance to use 50 to 75 ohm impedance
>transfomers. I built two of the ones featured in all recent ARRL
>Handbooks - took me about an evening, and total cost was about $30
>including the boxes. They work GREAT. When I put them into my system, I
>had one in backwards because of a stupid mistake, and the resulting SWR
>was 2:1. I figured out what was wrong and turned the transformer around
>and all was beautific.
>I run 1500 watts to them and they stay cool. I can't imagine why anyone
>would bother to do it any other way!

Raises an interesting question, but one beyond my quantitative abilities.
Assuming the autotransformers are built well - adequate wire size, proper
core, big-enough box, etc. - what is the expected loss in such a 50:75
transformer?  If I had that number, i think I could answer your question,
because according to TL (thanks, Dave), on 20m. my 230-odd feet of 75-ohm
hardline has an added loss of only 0.05 dB, when terminated on the antenna
end by a matched 50-ohm antenna or transmission line.  I suspect that's
less than 2 very good toroid transformers could deliver.

73, Pete Smith N4ZR 

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