[TowerTalk] Solenoid or Binocular configuration?

Steve Hunt steve at karinya.net
Sun Oct 21 04:36:13 EDT 2012


Roger,

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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