Paul Keinanen wrote:

Sounds like a step recovery diode (SRD) multiplier, which generates a
very broad spectrum.
......
I have a couple of SRDs but they seem to be optimised for 500MHz input
and I don't know if they would work at lower frequencies. I would assume
that the diodes I mentioned are some sort of SRD or "snap" diode so I
might pull one out and try it.

Paul OH3LWR