[TowerTalk] Placment of common mode chokes

[Jim Brown]

On Mon, 24 May 2010 14:29:13 -0400, Bill Ogden wrote:

>I think I understand the value of a choke made from coax passing several
>times through a 31 material core. My question is "where should these be
>located?" in real situations.

ALWAYS as close as practical to the point where the coax connects to the 
antenna (that is, up in the air). The length of coax between the choke and 
the antenna can act as an RX antenna for noise. 

>I see the large 31 cores are $7 each from Mouser.  It appears that several
>are needed for each choke. The cost is not unreasonable, but I do not want
>to obtain more than I need.

See my Cookbook. http://audiosystemsgroup.com/RFI-Ham.pdf  Also, look at 
page 36 for guidelines on bifilar chokes that can be wound on a single core 
with #14 THHN. 

73,

Jim K9YC