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

Maybe 2N4401 will work, I built some simple 1 transistor FM transmitters
that modulate the base.

If not, who sells dual varactors in small quantities?

JE

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

Since the 1N4007 isn't a dual, why do you require a dual varactor? I'd
expect diodes specifically made to be varactors would have less
variation from part to part with respect to capacitance than would some
other random diode.

Have you tried Mouser (as Professor suggests) or DigiKey, or some of
the surplus places like MPJA?

I've heard that 1N4007s commonly make decent PIN diodes. If that's the
case, if they really are made as a PIN structure, I would think they'd
make lousy varactors. Wide-tuning-range varactors are commonly
"hyper-abrupt" junctions, NOT PINs.

Cheers,
Tom