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Re: Topband: Choke material

To: Guy Olinger K2AV <>
Subject: Re: Topband: Choke material
From: Mike Waters <>
Date: Fri, 8 Sep 2017 20:22:23 -0500
List-post: <>
Hello Guy,

I don't disagree with this at all. The common-mode chokes I now use are
K9YC's design, except for one still on the coax in the shack feeding a TX

But I can personally testify that the TV deflection yoke cores I made were
useful at much higher frequencies. For example, I made and installed
common-mode chokes on 3 phase lines feeding some CNC equipment the last
place I worked. IIRC, there were about 12 turns of 3x10 AWG THHN wound on
it. They completely eliminated the RFI from a TIG welder in the same
building, operating at some ISM frequency (probably 13 MHz).

Having said that, I also installed some RF-rated Sangamo surplus mica caps
(remember those? ;-) between the phases (and maybe to ground, too) on the
equipment side of the choke. I never took the capacitors (IIRC .005 to .02
uF) out of the circuit to see what happened.

Other times, they prevented RFI in my shack at frequencies above 160 meters.

Just sayin'. Can't hurt to try them.

73, Mike

On Fri, Sep 8, 2017 at 7:21 PM, Guy Olinger K2AV <> wrote:

> Those chokes are of a material that is designed for audio frequencies. I
> can still remember the day's in my youth when I could hear the 15 kHz
> horizontal sweep frequency.
> I would not be using those for a frequency more than a hundred times the
> frequency they were designed for.
> Use the #31 material for 1.8 Mhz.  Go see K9YC's web page to see why.
> 73, Guy K2AV
> On Fri, Sep 8, 2017 at 3:30 PM, Mike Waters <> wrote:
>> Yes they are! I have used many of those ferrite cores for that purpose
>> over
>> the years. Wind as many turns of coax through them as possible. And make
>> sure there is no gap between the halves.
>> How they compare to stacked 2.4" 31 material toroids (which is what I've
>> used the past few years), I can't say.
>> 73, Mike
>> On Fri, Sep 8, 2017 at 2:23 PM, Carol Richards <> wrote:
>> > I have been cleaning out a shed with 50+ years of stuff. I found several
>> > yoke cores from the TV sets made in the 60's. Are they usable for common
>> > mode chokes?
>> >
>> _________________
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