In message , Jeff
writes

"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

An alternative (but similar) circuit is essentially the same as the
well-known two-diode fullwave (bi-phase) rectifier.

Single ferrite bead input transformer, trifilar wound with 2 or 3 turns
(say 32 -34 gauge). Bead typically 5mm long, 4mm dia, small hole, mu 100
- 200. One winding is the input (primary). The other two connected as
centre-tapped secondary. CT to ground. Diodes VHF/UHF switching/mixer
diodes. Output 'DC polarity' - either +ve or -ve (doesn't matter).
Output must have DC return to ground (if output is DC blocked, use RFC
or resistor - say 50 - 330 ohms).

Physical balance affects suppression of fundamental and odd harmonics.
Helped (maybe) if input feed is via series bifilar balun choke (2 or 3
turns on same type of bead as transformer).

Ian.
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