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Old November 11th 04, 05:42 AM
Dale Parfitt
 
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Default Update: Home-built air-gap variable capacitor


"Lars Janqqvist" wrote in message
...
Frightening the yaks, -=jd=- just had to say:

It wasn't nearly as difficult as I had anticipated.
I finished up with 14 rotors and 15 stators.

The meter says 7pF with the plates unmeshed, and 314pF with
the plates fully meshed.

The trickiest part was patiently (and subtly) straightening
the plates after assembly. Cumulative time spent building it
was probably 4 hours. After building the first one, you
realize that the plates don't have to be perfectly cut - they
just have to rotate all the way around without contacting
anything. Just as the Cajuns know that "looks don't make it
taste good", capacitor plates that aren't cut exquisitely neat
don't mean it won't... um... "capacitate"...

-=jd=-


re uneven plates: The linearity will suffer but unless you're
calibrating it to something (tuning dial, antenna load) that
shouldn't matter.


I don't see anything linear in F vs C for a resonant circuit. In fact, in
order to make it anywhere close to linear, one has to go to extremes with
the shape of the plates.

Dale W4OP