I would think a "W3JDR" would know that even harmonics are *much*
harder to obtain in nonlinear multipliers.

I guessed I missed Jim's comment in the earlier post, or I would have replied earlier.
Jim, I'm not not sure what you're trying to say, but there seems to be a sarcastic undertone to the way you said it.

Anyway, it turns out that non-linear single-ended elements are great generators of even-order harmonics. That's why the classical HF/VHF multiplier circuit is typically a single ended transistor amplifier with output and input tuned to different frequencies. If you bias the device so it is non-linear, then it becomes a natural harmonic generator. You can enhance even-order generation and supress the odd-order generation by using a non-linear 'push-push' stage, just as you can suppress even order harmonics with a 'push-pull' stage.

In either case, the important thing to remember is that symmetrical clipping or limiting generates mostly odd-order distortion and unsymmetrical clipping or limiting generates mostly even order distortion. The quantification of this is left to those more mathematically inclined.

Joe
W3JDR