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 manual is at ftp://bama.sbc.edu/downloads/hp/1169..._service_6.pdf

Ideas??

Scott
N0EDV

Scott wrote:

I recently picked up an HP 8640B Opt. 323 (8640B in a can) and wonder if
anyone has information on the external frequency doubler so that it can
use it's upper frequency position (512-1024 MHz). I want to get 902 MHz
out of it to test the feed for my parabolic dish's return loss (SWR).

I can build a diode doubler to generate harmonics and then put a 1/4
wavelength of shorted-end coax across its output to select the 902 MHz
harmonic, but I'd like to be able to tune all freqs between the 512 and
1024 MHz without building a lot of shorted stubs. How does HP do it
with their doubler? Bandpass filtering? Could one bandpass filter
cover that much range?? Maybe something as simple as a low pass filter
with an Fco of 1050 MHz or so, but with this, how would I keep the
fundamental freq (256-512 MHz) out of the output??

Thanks for any leads!


--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)