General Microwave 550 WWV Receiver

Bought this on eBay from a guy in Canada in late 2003. He added the extra holes around the meter and the display window under the meter. Said he was going to add a digital clock timed off of WWV which he never completed. He didn’t have the manual but claimed it did receive WWV signals. When I finally got it, of course, it didn’t receive anything. Primarily because the pair of 475KHz IF crystals were removed from the unit. My interest in this receiver was to get a 10MHz reference output for my test equipment and some of the radios I have, and if I got the 10MHz referenced to WWV, all the better. I was not able to track down a tech manual but I did find out that they were used very extensively in Canada and in some US AM Broadcast stations to calibrate the transmitters against WWV.

This receiver is actually a comparator that compares a local standard/reference to a 10MHz signal derived from the WWV 5 or 15MHz transmission from NIST Time and Frequencies Services. The local standard input can be any sub-harmonic of 400KHz, 2MHz, or 10MHz. Any deviation between the local standard being measured and the WWV signal is monitored as an audible beat note and as a rotating half moon pattern on the CRT display. When the local standard is exactly equal to the WWV signal the half moon stops rotating. Any clockwise rotation indicates local standard is high, counterclockwise rotation indicates local standard is low. The comparator allows you to calibrate your local standard to NIST accuracy. Thus I can say my local frequency standard is aligned to NIST.

 This is perfect for what I wanted to do. I could calibrate the 5MHz from my URQ-10 Frequency Standard against WWV as well as get a calibrated 10MHz output from the comparator for test equipment and radios.
With no manual I hand traced the circuitry as I disassembled it down to bare chassis for rebuild. Only problem with a hand traced scat is, I don’t know exactly what the circuitry is supposed to look like. It's possible that anyone along the way could have made some modifications and I just traced them, not knowing how it is actually supposed to be. I did eventually find a tech manual for a Lavoie LA800D a couple years later which is nearly identical to the General Microwave 550 and I was able to verify my tracing of circuitry was correct. Some disassembly pictures above. I striped it down to a bare chassis and rebuilt it using the scat I hand traced.
Here it is completed. Kind of  shame the way the front panel was hacked up. I may consider putting a clock in just to fill the holes as a future project. Came out really good even though. I was able to dig up a single 475KHz IF crystal. It does work with the single crystal but there is no way I can get the 50Hz IF bandwidth specified without the crystal pair. In the rear view you can see I added BNC connectors to have rear connections for the Antenna, Local Standard Input, and 10MHz output.

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