I notice the holding bolt is steel. Do you think this had any effect on your
measurements? I know that if you use this method on L-coil or the PI coil
in a linear amplifier, the bolt heats considerably.
From: "Tod" <firstname.lastname@example.org>
Sent: Sunday, August 28, 2011 3:51 PM
To: <email@example.com>; <firstname.lastname@example.org>
Subject: [TowerTalk] Fabricated common mode chokes and their impedances
> This probably has a limited audience but I do know that there are some
> readers on this list interested in fabrication of high impedance common
> chokes for their stations.
> I built and measured 18 of this type of choke during the past week. There
> a write-up on my web site which shows how they were fabricated, how they
> were measured and the measurement results. I used Fair-Rite 2.4 inch
> diameter type 31 toroidal cores and small diameter [RG 59 size} coax. I
> measured the magnitude of the impedance for each of the chokes on the 160,
> 80, 40, 20, 15 and 10 meter bands. There are also attenuation values for
> each choke [specific to the 50 ohm measurement circuit]. The results are
> shown as a series of graphs for two cores, three cores and four cores with
> 3, 4, 5, 6, 7 and 8 turns on the core bundle.
> These graphs should provide guidance to those fabricating their own common
> mode chokes.
> The site is
> The article is under Experiments & Measurements
> "Measurement of Chokes made using type 31 material cores"
> My work is an extension of material found in the excellent paper on this
> subject written by Jim Brown, K9YC, which has been mentioned here before.
> Tod Olson, K0TO
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