[TowerTalk] Cutting a FT-240 type 33...in half ??

Steve Hunt steve at karinya.net
Tue Feb 10 08:44:55 EST 2015


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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