Topband: Toroidal common mode choke

[Jim Brown]

On 11/17/2012 9:12 AM, Bill Conwell (home) wrote:
> I've seen articles that studied the optimum number of turns for air-core
> chokes, but don't recall seeing any for toroidal chokes.  Can anyone offer a
> pointer (or empirical data) that might guide me.  (20 turns?)

See http://audiosystemsgroup.com/RFI-Ham.pdf   which includes both 
measured data for many choke configurations and core materials, and 
specific recommendations for winding transmitting chokes for the ham 
bands. For 160M, Fair-Rite #31 material is the weapon of choice, and 16 
turns of a pair of #12 enameled wire (connected a parallel wire 
transmission line) makes a very effective choke for 160M and 80M, with 
Zo on the order of 50 ohms. #12 THHN works as well on 160M and 80M, and 
has bandwidth good to at least 20M, with Zo of about 100 ohms.  If that 
level of mismatch concerns you,  remember that it's only a few feet of 
line, less than 1/200 of a wavelength at 1.8 MHz.

73, Jim K9YC