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[TowerTalk] Re: 4 sqr feedline suggestions from N0AH

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Subject: [TowerTalk] Re: 4 sqr feedline suggestions from N0AH
From: Dinsterdog@aol.com (Dinsterdog@aol.com)
Date: Tue, 7 Sep 1999 14:43:02 EDT
TO  N1RJ

Roger,

Thx for the suggestions to try 50 ohm feedlines vs. the 75 ohm feedlines I am 
using now.....I thought it was a good question, and a point I missed in 
earlier postings- so I'm posting this reply to TowerTalk.......

I spoke to several 4 sqr owners who used the comtek coupler prior to 
construction......I thought 50 ohm looked pretty good too but those who tried 
50 ohm feedlines,  went back to go back  75 ohm..........looking on page 
11-51 on ON4UN's 3rd edition, he states...

"It has been found in practice that with a hybred coupler, having a design 
impedance of 50 ohms, it is better to use 75 ohm cable to feed the array 
elements.  The transformation is such that the impedenace presented at the 
hybred coupler result in less power being dissapaited in the dummy load 
resistor......"

To be honest, the more I research the subject,  of why I can't get the array 
to drop any less than 5% into the dummy load,  is perhaps due to diameter of 
the radiators (Q Factor)......

If I used 25Rohn tower sections and full size 1/4 wave elements....I think 
then I'd see a difference- and maybe get below that "mythical" 3% range-  

I've just about ruled everything else out without having access to more 
technical measuring equipment...  73  Paul     N0AH



 

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