----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <topband@contesting.com>
Sent: Saturday, November 17, 2012 1:12 PM
Subject: Re: Topband: Toroidal common mode choke
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
The question was for RG-58. Have you made tests using that and published it?
Also the difference between Mix 31 and 43 is not great and was used for
decades successfully before 31 was introduced.
Carl
KM1H
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