In the PPT you linked, there are slightly fewer effective turns on the
binocular than on the tall stack; he's comparing 3 complete turns
through a stack of 8 toroids, with 3 turns through part of the stack and
2 turns through the remainder. You'd expect the relative impedances to
be (8*3^2) and (4*3^2+4*2^2) for the tall stack and the binocular
respectively; that's an impedance ratio of 1.38:1 which is about what
the chart shows consistently at frequencies well below the SRF.
I guess the shift in SRF is then simply down to the difference in
inter-winding capacitance between the two arrangements.
Steve G3TXQ
On 10/02/2015 11:35, Ian White wrote:
Interesting question about binocular arrangements of cores (two short stacks of
cores side by side, vs one tall stack). I found K9YC's comparative measurements
[1] but am struggling to explain either (a) the shift in resonant frequency or
(b) the difference in |Z| magnitude.
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