"John Popelish" bravely wrote to "All" (10 Jan 06 22:14:12)
--- on the heady topic of " 1N4007 varactors"

JP From: John Popelish
JP Xref: core-easynews rec.radio.amateur.homebrew:90859

JP Steve Nosko wrote:
JP (snip)
Don't (some) zeners generate noise???...or is that only near the breakdown
reigion?

JP I think that whether noisy or not, the noise generation mechanism
JP kicks in, only when the zeners are reverse conducting via the zener
JP breakdown process, so if you keep the voltage well below the zener
JP knee, say, half of that, they are not particularly noisy compared to
JP other diodes. So, yes, only near the breakdown region, especially
JP just below the rated voltage (low reverse current).


I never tested a zener when used as varactor but I think these have a
much greater reverse saturation current (even far below breakdown
threshold) and it is this that might cause comparatively more noise
than a conventional diode with a tiny leakage current. Well, at least
that is what the junction noise equations would seem to indicate.

A*s*i*m*o*v