On Wed, 21 May 2008 17:00:40 +1000, Alan Peake
wrote:

However, I have
found two pieces of equipment in the junk box which just use diode
multipliers. One is an old Electrophone UHF CB radio which multiplies
the crystal oscillator by 17 (I think, from memory)then uses helical
resonators to filter the desired harmonic.


Sounds like a step recovery diode (SRD) multiplier, which generates a
very broad spectrum. In extreme multiplication situations a tunable
harmonic analyser could be used to select out a single harmonic from
the broad SRD spectrum (mix down with a VFO, filter with a crystal
filter with bandwidth comparable to the fundamental and mix up the
filtered harmonic up to the original frequency using the _same_ VFO,
effectively canceling out any VFO drift).

However, since there have been prescalers available for quite a while
for satellite-TV indoor units, which are capable of at least 2 GHz,
why not use a PLL. Put a VCO at 1296 MHz, use a divide it by 64 using
the prescaler and phase lock it to a 20.25 MHz crystal. With such high
reference frequency, the loop filter can be quite broad, greatly
attenuating the VCO phase noise.

Paul OH3LWR