diode. A 70 cm input signal (e.g. 432 MHz) results in a 23 cm outputsignal (1296 MHz).
Efficiency is about 50%.
It looks like as if tube trimmers are used. The varactor and capacitor of 0,5 pF look
as if that are hard-to-get components. One can make small capacitors with values less
than 1 pF by twisting to pieces of wire.
Principle frequency tripler;