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
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