1.One plate - ground - is a metal case.
2.Bearings are those of joystick. So capacitor's
   elements are two isolated from ground aluminium
   plates - one for PIC1 oscillator and another for
   PIC2 oscillator.
3.Dust is not a big trouble for thick aluminium plates.
4."poor contact in the bearing for RF currents" does
   not matter, since curcuit is mounted with aluminium
   plates and get connected via flat ribbon cable, a sort
   of used in dot printers.

   The idea of "fixed plates (of a cap) into which is
moved a dielectric" is highly interesting. I need to think
about it. Thank you.

   Mike.

>
>    "Using two variable capacitors"
>
> Dust and variable capacitors mentioned in the same
> sentence - is this a recipe for future trouble?
>
>    - dust between plates
>    - dust in the bearings of the movable portion
>    - wear in the metal 'bearing'
>    - poor contact in the bearing for RF currents
>
> How about two fixed plates (of a cap) into which is
> moved a dielectric - to change the capacitance.
>
> At least this way the dependence on a metallic
> bearing also carrying RF from one cap plate in a
> dusty environ is eliminated ...
>
> Jim
>
> From: "Mike Singer" <mike@POLUOSTROV.NET>
> >
> >    I don't like much the optical idea, because of dusty air.
>>.
>>.
>>.
> >    Using two variable capacitors, as I posted, we already
> > have two frequencies, and getting the difference is only
> > a question of programming technique.
> >    Moreover, capacitor plates may be made in overall design,
> > since one capacitor plate of PIC oscillator is Ground.
> >
> >    Mike.
> > -------

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