High-power varactors

[Bob Bruninga]

On Sat, 29 Nov 2003, Andre Kesteloot wrote:

> The idea of using the drain-gate capacitance of biased-off power MOSFETs
> as high power varactors is interesting.

What is it about varactors that makes them better than just a diode as a
high power mixer?

I need to build a high power varactor mixer to take a 220 MHz exciter and
a 27 MHz exciter and yield 247 MHz AM.  Filter the result and use it as a
means of generating a watt or so at 247 MHz for the uplink for the MARS
satellite we are building.

We chose the satellite uplink so that any MARS member with an
old CB set and a source of 220 MHz could put something together for the
uplink.

I remember seeing a high level mixer made from just a BUNCH of 2N4148
plain old signal diodes in parallel... Whats the advantage of the
varactor?  Just higher percentage products?

Bob