On Dec 16, 2019, at 1:20 PM, Eric KE6US <eric.csuf@...> wrote:

?

Virtually ANY diode will work, some better than others. I have a number of projects where I used a red LED as a varactor. I usually got from low-teens pf to ~50 pf. Smaller ones tended to be better than larger ones. Red was better than other colors which have a much more limited range. The only problem I found was light sensitivity. You have to block the lens (tape, dipped in paint, whatever) or it will pick up 60 cycle variations from lighting and other weird effects.

Didn't have much luck with gp diodes. They work. Just not as much range as red LEDs. I've used them since about 2005. A couple are still plugging away and work fine.

Eric KE6US

On 12/16/2019 11:42 AM, Jerry Gaffke via Groups.Io wrote:

I'm curious how the 1n4001 compares with purpose built varactor diodes.
Figure 3 here shows it going from about 20 to 5 pf as the reverse voltage goes from 0 to 10 volts.
? ??
Would be interesting to verify that with measurements, trying several different manufacturers.