In article , "W3JDR"
writes:

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" Starting with a perfect square wave at f1, bang the hell out of a =
diode
with it, and then bandpass it and the 3rd harmonic (f2) separately, =
then
mix them to get f1, f2, f1+f2, and f1-f2. Using a doubly balanced =
mixer
will get rid of f1 and f2, then notching out f1+f2 will leave f1-f2,
which will be 2f1, that non-existent second harmonic."
=20
Oh yuchh...that sounds painful!=20
Why not just distort the symmetry of the square digitally (like drive it =
into an exclusive-or with a small delay on one input) to make a short =
impulse, then bandpass filter the output? Or staying in the purely =
digital domain, use same said exclusive-or and delay one of the two =
inputs by t/4 (t=3Dperiod of input sq wave) and get a 2*F square wave =
out.

...or just use a small toroid transformer, a pair of diodes arranged
like a full-wave rectifier for wideband frequency doubling? :-)

While using digitial techniques sounds cool at first, the above
technique can generate all kinds of PM that isn't noticed on time-
domain viewing with a scope. There are many ways to cure that PM
or incidental FM but all involve lots more circuitry than the simple
diode doubler which can be inherently broadband over half an octave.

Depends on the application of the multiplier and the overall specs
on purity of the multiplied RF.

Len Anderson
retired (from regular hours) electronic engineer person