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Re: [TowerTalk] Running Coax in the plane of a VHF antenna

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Subject: Re: [TowerTalk] Running Coax in the plane of a VHF antenna
From: "Jim Brown" <>
Date: Thu, 06 Nov 2008 18:58:35 -0800
List-post: <">>
Yes. You need to look at data for the specific ferrite part, not 
the generic data for the material. 

A wire going through a ferrite core looks like a parallel resonant 
circuit, the frequency of which is determined by the dimensions of 
the ferrite part and its chemical composition. So a core that is 1 
inch long will have a different resonant frequency than one that 
is only 0.25 inches long. 

The Fair-Rite catalog is VERY detailed, and includes impedance vs 
frequency data for almost every part they make. It's online. 

There's a tutorial that covers this on my website.


Jim K9YC 

 --Original Message Text---
From: Paul Baldock
Date: Thu, 06 Nov 2008 15:10:39 -0800

This is quite solid engineering, except that #61 is not a good 
for 146 MHz. #43 would work much better. Study Fair-Rite data for 
beads you want to use 

The charts I see show permeability verses frequency. The Type 43 
chart only goes up to 100MHz. The Type 61 chart goes up to 
1000MHz. Type 61 peaks at 25MHz. Type 43 peaks at 5MHz, but is a 
much higher peak. At 100MHz both types have similar permeability. 
I chose Type 61 because it is specified to a higher frequency.

Am I misinterpreting something?


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