The type XCU-50 Crystal Calibrator Unit is designed expressly for use within HRO receivers. It utilizes an electron-coupled oscillator circuit controlled by a dual crystal (Valpey type DFS). This type of crystal provides two crystal-controlled marker frequencies of 100 kilocycles and 1 megacycle. When plugged into the Crystal Calibrator Socket, the XCU-50 output is loosely coupled to the first R.F. amplifier input circuits. Selection of either the 100 kilocycle or 1000 kilocycle crystal-controlled signal is made possible by the front-panel mounted Calibrate switch on the receiver.

INSTALLATION: The XCU-50 calibrator is installed in the receiver by plugging the unit into the Crystal Calibrator socket, on top of the chassis. A slotted-head screw mounted through the top of the unit is provided to bolt the unit to the chassis.

A trimmer capacitor, is connected across the crystal to permit adjustment of the frequency of the 100 kilocycle output marker when the unit is operated at locations where the temperature is vastly removed from that of normal room temperature. This capacitor should never require adjustment unless such abnormal temperatures are experienced.

Source: The National HRO-60 Instruction Manual

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