>2nd question-   Polling for input on Varactors vs air variable capacitors.
>I recently purchased 16 RF tuner capacitors at $1.25ea from Electronix
>Express only to find that there is no such thing as a mating knob for them
>in the USA (they have two flat sides on the tuning shaft and a threaded
hole
>in the center of that.  Also, the shaft is extremely short).  I've
>considered using a varactor tuned oscillator circuit with the 120pF
variety.
>Saw a web page that uses two varactors chained together with the tuning
>voltage at the  tie point.  The circuit web page mentioned the low Q of
>varactors and  I'm  concerned about this affecting my circuit negatively.
>I'm aware of homebrew amateur 2meter transcievers using varactors and their
>usage in radio receiver tuners.

I think you should check out the Hyper-Abrupt junction Varactors that are
available. I think you will find that these give a higher Q than older
varactors. You do not state what frequency range you want, but if you are
talking in terms of 120pF then I suspect it will be HF rather than broadcast
or VHF. To get this you may need several diodes in parallel to get the
capacitance you need, but it is a while since I looked at varactor data
sheets so am not sure of the capacitance ranges available these days.
Certainly every TV and Video tuner has them in.

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