[Elecraft] How varactors work

[Lyle Johnson]

> My guess is that the "speed"of the varactor diode is too slow for it to
> respond to bias voltage changes at RF frequencies...

I used to think the same thing, but it seems to not be the case.  The uplink
400 bps PSK demodulator in the command decoders of AO-40, for example, use
reverse-biased diode junctions (varactors) to tune a PLL in an oscillator at
10 kHz.  No diodes are *that* slow! :-)

See "The Art of Electronics," 2nd Edition, pp 297ff.

PIN diodes, used for signal routing in the K2 (a 1N4007 rectifier), *are*
especially designed to be slow...

73,

Lyle KK7P