Heathkit HD-20 and Homebrew Crystal Calibrators

Every vintage receiver should have a crystal calibrator to check dial calibration of both the receiver as well as the transmitter, to ensure FCC rule compliance. Some receivers have a built in calibrator. You can also have an external accessory crystal calibrator. The Heathkit HD-20 is a 100 KHz crystal calibrator which runs off 9 VDC. Here are the schematic and alignment instructions:

For a full copy of the manual, go to: http://tubularelectronics.com/

Here are pictures of mine, with the attached DC battery eliminator and coax cable with "T" ready to attach to a receiver. The trimmer capacitor on the back adjusts the frequency to zero beat with WWV. The coil on the back peaks the output signal on the highest receiver frequency band.

Here are pictures of a Homebrew unit I made based on a 4 MHz crystal and TTL dividers. It outputs frequencies of 4, 2, and 1 MHz. It also does 200, 100, 20, 10, 2, and 1 KHz. The output connectors are set for a level appropriate for a receiver calibration or a scope frequency calibration. It can also be used in a TTL breadboard circuit for a highly accurate clock generator. If you want your scope time base exactly on, this is a good way to adjust it. You can zero beat the 1 MHz standard exactly to WWV and all others are good, since they are generated by frequency division circuits. This is more of a test bench device.


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