[TowerTalk] Shunt Feed Mystery

[Jim Brown]

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. http://k9yc.com/2018Cookbook.pdf  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 k9yc.com/RFI-Ham.pdf and 
in the ARRL Handbook.

73, Jim K9YC