"Scott" wrote in message
...
Searching Google, I was able to find a copy of the manual for the
frequency doubler unit (HP 11690A) which conveniently describes the
operation and has a schematic. I could make one, except there is one part
that is just labeled as a transformer (T1) with three windings. That
probably wouldn't be too hard to make, but no idea how many turns for each
winding...


The purpose of the transformer is to split the incoming signal in-phase and
apply to the 2 input port of the double balanced mixer. The number of turns
will depend a bit on the ferrite that you use for the core, I suspect that a
2 hole bead would be best, but a toroid would probably do as well.

73
Jeff