> >
> Interesting Tom. Why not discuss how the coil form (bobin?) affects the
> capacitance turn to turn? I have a ceramic bobin where the wire only
touches
> the ceramic only at a few points each turn. There is a lot of air beetween
> the turns. Low self capacitance then?
>
> ??? de Hans SM5KI
If the coil form dielectric constant is equal or larger than the air
dielectric constant, and that material has no losses at frequency in use, I
don't see how stray capacitance can increase.
I tuned circuits with small alumina pads between lines, but it was at 12
GHz, not HF.
The only way to decrease the coil turns self capacitance (to rise self
resonance), is to use a thinner wire.
Unluckily this is not applicable where power is large, and a 2-30 MHz
amplifier should have a minimum of two switchable plate chokes to be really
resonance free.
The "technique" to wind chokes leaving gaps between turns only shifts
resonances, and finds out a cheap compromise that utilyzes ham bands are
enough separated to allow it (at least until the advent of WARC bands).
73,
Mauri I4JMY
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