The model XCU-400 Crystal Calibrator unit is designed for operation with the NC-400 communications receiver. Each calibrator is factory-adjusted to zero beat with station WWV, and will accurately provide 100 kc and 1 mc marker frequencies for the NC-400 receiver.
OPERATION: The XCU-400 Crystal Calibrator provides an accurate means of checking the frequency calibration of the NC-400 receiver dials. The Calibrate switch, on the receiver panel, provides selection of the 100-kc or 1-mc marker frequencies. The Off position removes B-plus from the calibrator. The Tune position of this switch is not used for calibrator operation.
CALIBRATOR CHECK: The NC-400 receiver provides a control for adjusting the crystals in the calibrator to WWV, by an adjustment in an opening in the calibrator case. Check the adjustment by tuning station WWV on the receiver, turning the Calibrate switch to the 100 kc position, and zero-beating with WWV. A small readjustment may be required to compensate for crystal and component aging over long periods.
Source: The National NC-400 Instruction Manual
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