On 2006-07-25, Tim Wescott wrote:
If you're using a load capacitance you're not using the crystal's
natural resonance frequency -- that occurs at the series resonant frequency.

Point taken. It's a crystal cut for a parallel resonance with a specified
load capacitance (18p, I think).

Were you using the same crystal for both circuits? The same LED?

Not physically the same parts, but identical parts purchased at the
same time.

I would try this out with a trimmer and parallel cap that mirrored the
expected range of the varicap, _then_ I'd add the extra variable of an
unknown varicap.

That's an obvious idea I had totally overlooked!

--
Ben Jackson AD7GD

http://www.ben.com/