While sitting in the patio and browsing through E-Bay for any bargains, I came upon a signal generator, model HP8640B which the seller described as needing repair. I had 2 days to bid while I did some research on the web and discovered it was a well known generator and also found several sites that had solved some problems encountered with this unit. Someone had made a small bid of $10, so I figured it would be worth at least $100 even when not functioning. Well, when the bidding ended, I wound up getting it for $60 including $15 for shipping. The seller contacted me and said he would sell me the original manual for an additional $25 which was well worth it.
When the box arrived the first thing I did was go over the manual which also described how it functioned. I discovered it's mostly a UHF power oscillator followed by a bunch of frequency dividers to create the other bands, and phase-locked using a very simple PLL circuit that adjusts the voltage on a varactor which is part of the main cavity oscillator. When turning it on, the dial lights came on but showed no output on any band setting.
I did some trouble shooting and found an unfamiliar output device that wasn't amplifying the signal before being sent to the attenuators.. Searching on Google, I found a nice site by Mark VE7CA in British Columbia who knew exactly how to repair that output amplifier, I soon had it working since I already had the MAV-11 chip in my parts supply. Another good site is from Jose EB5AGV in Spain who showed how mechanical repair may eventually be needed on some switches and controls.
This signal generator has an input for a 5 Mhz reference signal. Already having 10 MHz availabloe from the Z3801A, a simple divide by two circuit was constructed with a tuned 5 MHz circuit to supply a sine wave reference. For extreme accruacy, I use my referenced HP frequency counter along with the generator. It is nice to be able to output a 1 microvolt signal to check a particular receiver or transverter at an accruacy, say for example 144.200000 Mhz.
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