Winter 2006 Issue

MICROWAVE

Troubleshooting a 10-GHz Converter with a Homemade Noise Generator

By Chuck Houghton, WB6IGP

My last column, in the fall 2005 issue of CQ VHF, covered the relay switching (transceiver) circuit I used for controlling the switching of my microwave converters. Who could have known that I would be trouble-shooting the switching circuits and the entire 10-GHz converter system? What happened follows, along with a description of a simple, homebrew noise head I used to trouble-shoot in my 10-GHz converter system. I will also cover how you can put together a noise head as part of your microwave test equipment.

Trouble raised its head while I was cleaning the shop shelf of my shack, where my 28-volt, 25-amp Astron power supply for my microwave converterís TWT (traveling wave tube) amp is located. I had removed the cover of the power supply while I was making an adjustment. Nearby was a stack of boxed stuff that had previously occupied the shelf. Shop cleanup created the setting for disaster. The 10-GHz rig was working just fine and was tuned to our microwave groupís 10-GHz beacon on Mt. Miguel. The rig had just been moved. I was making a quick test of the beaconís signal quality, confirming system operation.

The next thing that happened changed the schedule for the day. I had to solve the problem in the entire 10-GHz system, from the power supply to the dish antenna feed. A metal pin rolled off the top of the pile of boxes where it had been perched and fell into the 28-volt power supply, shorting out the supply. Needless to say, I shut down the power supply and removed the pin ASAP!

I turned on the power supply, and you guessed it. . . . It appeared to have blown and the converter was dead. That started my day. A short beacon check ultimately became a full day of trouble-shooting a power supply, and at that point early in the day, who knew what else. I will describe the procedures I went through to determine what could be repaired.

Photo A. Close-up of the surplus PC board and components as placed on the board.
 

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