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Re: [TowerTalk] Solenoid or Binocular configuration?

Subject: Re: [TowerTalk] Solenoid or Binocular configuration?
From: Steve Hunt <>
Date: Sun, 21 Oct 2012 09:36:13 +0100
List-post: <">>

Interesting question!

I just tried a measurement using four FT240-31 cores - all I had spare in the component draw. I wound 9 turns of RG-400 on a stack of four cores. The CM impedance peaked at 13,400 Ohms and the CM phase angle was within +/-45 degrees from 2.28MHz to 4.84MHz.

Using _the same length_ of coax gave me 12 turns on a 2x2core binocular, and that reproduced the CM impedance almost exactly: 13,700 Ohms peak and +/-45 degrees from 2.3MHz to 4.87MHz. Reducing the number of turns to 9 shifted the peak impedance much further up in frequency. So I don't think it follows that you'll get the same results using _the same number of turns_ in the two configurations.

Remember, these are parallel-tuned circuits - that's why we get the high peak in CM impedance. The stray capacitance is determined by number of turns, the length of turns, and by the "dress" of the windings. That changes between the two configurations, so although the effective inductance may not change, the stray C does.

Hope that helps some,
Steve G3TXQ

On 21/10/2012 03:23, K8RI wrote:
My question is about the difference between the 6 cores stacked or two stacks side by side. Would there be much difference between them as far as the resistive component of the common mode choke. These being toroids I would think the magnetic fields are pretty much contained inside each core and the associated winding(s) and doubt there would be much difference between configurations.


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