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Re: [TowerTalk] Shunt Feed Mystery

Subject: Re: [TowerTalk] Shunt Feed Mystery
From: Jim Brown <>
Date: Fri, 13 Dec 2019 11:06:18 -0800
List-post: <>
On 12/13/2019 10:49 AM, RT Clay wrote:
In ON4UN's book there is a description of a large feedline trap that can be 
used to decouple a dipole. Basically you have the dipole feedline wound in a 
large air-wound coil (4 inch sewer pipe) resonated by a capacitor. I am using 
this to decouple the 80m dipole on my tower.

This is a high-Q equivalent to the low Q of a well-designed ferrite choke. The ferrite choke typically has a circuit Q on the order of 0.5, making it quite broadband. That low Q value is the result of loss coupled from the ferrite core, so a well-designed choke must limit common mode current so that there is no over-heating. More conceptual explanation is in and in the ARRL Handbook.

73, Jim K9YC


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