....impossible to tell! nobody ever characterized them for high
frequency use. the usual effects of the varactor are pernicious! they
are crucial for low phase noise of the VCO using them. the only truly
effective way to check is build one and measure the performance with a
spectrum analyzer or a phase noise meter, both expensive items. my
recommendation is to build one and try to listen to its signal on a
receiver (stable one!), if the note is clean and not ragged it's OK. if
not the VCO is too noisy for use. don't be afraid to check more than
one diode in the same circuit. experience has shown that some units
perform better than others.
Saandy 4Z5KS


JE wrote:
The common 1N4007 seem to work for HF but what is the max. frequency they
can be used as varactors?

And how about zener diodes?

JE