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,
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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