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Re: [TowerTalk] Phase Relation of Different Cables

To: Mike <>,
Subject: Re: [TowerTalk] Phase Relation of Different Cables
From: Jim Lux <>
Date: Thu, 15 Mar 2007 08:57:01 -0700
List-post: <>
At 08:22 AM 3/15/2007, Mike wrote:

>Questions: what is a method for determining the phase relation of a
>pair of cables?  How to adjust the cables to have the same
>phase?  The cables are  made of two different kinds of coax, FSJ-4
>and RG 213.  The cables are different length.  One of the cable
>combinations is more than a wave length at 7 MHz.  The reason for the
>question is the desire to move all the antenna switching mechanisms
>off of the tower to the base.

Several questions..
1) How closely do you need them to match?
2) What bandwidth do you want the matching over?
3) How well behaved is the feedpoint impedance of the two antennas?

One way is just to make all the cables the same length (coiling up 
the excess) which has the advantage that they'll track well over 
frequency.  This might be termed an "equal time delay" approach.  If 
you want to trim a cable, you can terminate the far end in a short or 
open, then use any sort of antenna analyzer to sweep it and find out 
where it's a half wavelength, etc.  Trim all the cables so they 
"null" or "peak" at the same frequency.  You can just add cable (of 
any kind) to the end of the existing run to make it longer, so that it matches.

jim, w6rmk 


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