On Sat, 07 Jan 2006 17:26:23 -0500, JE wrote:

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

I've used them at low VHF, the limiting factor there is minimum
capacitance my be too high for some VHF uses.

And how about zener diodes?

As varicaps? Some are ok some very poor. You require a breakdown
voltage well above the applied bias.

Allison