Topband: Common mode chokes

[Jim Brown]

On Sat, 04 Jul 2009 10:16:23 -0400, Pete Smith wrote:

>Take a look, and tell me what you think!

Good work! Several comments. First, since your primary interest is 
HF, you'll get FAR more bang for the buck with WOUND chokes, as 
opposed to a string of beads. The reasons why are well documented in 
my tutorial, so I won't go into it here. Second, although the #73 
beads have relatively low choking impedance as compared to a wound 
choke, you make them do more by turning the common mode circuit into 
a sort of voltage divider by taking it to ground. Third, for even 
more noise suppression (if you haven't already hit the limit), I 
suggest the same centertapped configuration combined with wound 
chokes using the guidelines in my Cookbook. It's simply "if a 
little;s good, more's better." Fourth, if you are going to use 
beads, #73 is a good choice, since they are primarily resistive, not 
inductive, at HF, which means that their interaction with feedline 
length is minimal. 

If you're going to do a wound choke, I'd suggest 7 turns of the coax 
through the "big #31 clamp-on" specified in my Cookbook. 

73,

Jim Brown K9YC