Thanks for the input Peter and Alan,  I was considering using them in a grid
dip oscillator.  If a varactor is used, I wonder if it would need to be
buffered?  I saw that the Motorola varactors are discontinued and even some
of the varactors on digi-key are discontinued and only available in a
surface mount package.  NTE makes some varactors in a TO-92 type case.  I'm
starting to wonder if a varactor is not the correct part for a GDO circuit?
There was a NTE618 AM tuning varactor.  If I tied them together to isolate
the tuning voltage in the oscillator circuit, the capacitance would be
halved and in the range of 250pF but with low Q and possibly the need for
switched-in fixed capacitance values?
Thanks/regards,
Mike
----- Original Message -----
From: "Peter L. Peres" <plp@ACTCOM.CO.IL>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, August 10, 2001 8:07 AM
Subject: EE: varactors vs. air variable caps and LED windows


> You don't say what frequency but 120 pF suggests low HF or lower.
> Varactors have problems if the RF amplitude is comparable inmagnitude to
> the control voltage. This is almost always the case in equipment not
> designed to work with varactors. The Q is at least one order of magnitude
> lower than that of an air variables. Plus they are prone to
> intermodulation and other effects if used near a front end that can be
> overloaded.
>
> Apart from that, every TV and VCR tuner manufactured in the last at least
> 25 years used and uses varactors and there seem to be no serious problems
> so it depends on what you really do.
>
> Peter
>
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