Parametric operation is when you have a parameter such as diode
capacitance
that varies with voltage. The non-linearity of the parameter makes it act
as
a multiplier, mixer or an amplifier. Parametric amplifiers (they need to
be
'pumped' with an oscilllator) used to be very popular for microwave use.
If
you have inadvertently make yourself a parametric amplifier with your
diode
it could oscillate given the right conditions and do all sorts of strange
things. In your hands, this is a strong possibility. 8-)


I think you have a point Leon. Paul, use a Schottky diode, (HP 5082-2835 or
similar), use ZERO lead lengths. Make your PCBoard for the multiplier double
sided, drill a hole the diameter of the diode length, wrap a copper tape
ground from top to bottom on one edge of the hole, and drop the diode in the
hole and solder both ends. One end to the ground tape, the other to the land
to the filter for the harmonic you want. Then, drive with not more than +10
dBm of fundamental and hope a lot. It may STILL oscillate, but you've
maximized your chances. When you start getting output from the filter (on
the desired frequency which ought to be the only output you can get with the
filter in place) you can start matching the input to the diode with "L"
networks to maximize the output. Generally, the diode looks like a quite low
impedance so the capacitor used, ought to wind up on the side of the
inductor AWAY from the diode.

You can use an MMIC in the same manner to generate harmonics. Overdrive it
and under feed it with DC. More output, more chance of self oscillation if
you don't pay attention to detail.

A superior (less touchy) method of harmonic generation is just a full wave
diode rectifier. Using signal diodes and a center tapped transformer, make a
full wave doubler. Ground the DC out with an RF choke and you have 2F the
input frequency with good suppression of the fundamental and odd harmonics
built in. It's then a lot easier to filter the rest of the undesired out. Do
two of those to get 4F out rather than trying to do it all in one stage.
LOTS more efficiency.

W4ZCB