RadioBanter - View Single Post

April 1st 06, 05:51 PM posted to rec.radio.amateur.antenna

On Fri, 31 Mar 2006 21:40:46 -0600, (Richard
Harrison) wrote:

Yes. I think turn-to-turn capacitance doesn`t amount to much and won`t
bypass the coil as you have 100 small capacitors in series, so their sum
approaches zero.

Hi Richard,

This "approaches zero" capacitance for a coil has been tossed out so
many times it is approaching infinity.

For the commonplace coils in these applications, we have rather
non-trivial self capacitances. Why, when this evaluates to on the
order of 10-12 pF, that so many feel it incumbent to dismiss mutual
capacitances, then it does not follow.

Yuri's 60 turn coil may have 60 series capacitors, but it also has 60
parallel capacitances too. A back-of-the-napkin calculation for one
turn-to-turn capacitance finds
23.3pF
If we look at the capacitance between the first and last
0.2pF

The capacitance seen at the first loop, then, is a combination of
series/parallel capacitances to all other windings that, on average,
approaches a dozen picofarads.

The apparent capacitance based on reported resonances and modeled
reactance is on the order 12-14pF.

So, across the board and considering that this is RF, and HF at that,
the dismissal of capacitances are unwarranted.

73's
Richard Clark, KB7QHC