In article , Paul Burridge wrote:
What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

Not radio, but interesting nevertheless. The older Hewlett-Packard cesium
clocks, ie 5060/61/62 vintage multiplied a crystal oscillator up to 90 MHz in
several stages. This fed into a step-recovery diode that sits in a cavity, and
has 12.631... MHz applied to the SRD bias. The cavity selects the ***102nd***
harmonic ie 9180 MHz, and there are also sidebands at +/- 12.631.. MHz This is
then fed into a hi-Q cavity tuned to the upper sideband ie 9192.631... MHz
which is the desired cesium transition frequency.

Adjusting the whole thing was a bit fiddly, and there were also some
factory-set adjustments that you NEVER TOUCHED unless you had plenty of time
and a squillion dollars worth of test gear. This was all a 1960's design and
was a bit of a stretch. The newer (5071) clocks do things QUITE differently.

Steve Quigg