kb8tq@n1k.org said:

How would temperature effect that?  For that matter, how does temperature
effect the typical mechanical capacitor?  Does anybody play fancy tricks to
cancel out the mechanical motions?  (like the mercury pendulum - as the
pendulum rod expands the mercury expands in the other direction to keep the
CG the same)

--
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On 11/4/2016 12:34 PM, Hal Murray wrote:

The variable tuning capacitor in one of the military "frequency meters" (I
forget which one, BC221 leaps to mind) had a small disk on an adjustment screw
that worked against a bi-metallic strip "diving board" to make a temperature
sensitive trimmer capacitor.  I suspect, however, that it functioned more to
compensate the inductor than the variable capacitor that was very robust.

Before synthesizers, I built a VFO for a homemade receiver using one of these
cannibalized from a freq meter.

Wes Stewart, N7WS

On 11/4/2016 1:35 PM, Wes wrote:

I guess this list allows attachments so here are some photos.

VFO_1.jpg shows an overall view.  There are two trimmers seen on the end frame
that line up with the holes in the cover.

VFO_2.jpg is another view with the temperature compensating trimmer just visible
behind the circuit card.

VFO_2a.jpg is a closer view.

HI

If you use a good wire wound pot and run it off of and oscillator EFC source (not
all have them), the temperature effect is pretty much zero. You are using the pot
as a ratio device.

A mechanical cap that is part of the heated region of the OCXO (the normal case)
has already been taken into consideration when the OCXO set point is adjusted to
compensate it.

Bob