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100 kc calibrator with 10 kc markers

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The versatile neon-bulb sawtooth oscillator can he used to modulate a 100 kc crystal calibrator and obtain 10-kc. marker intervals. The circuit shown in Fig. 1 uses a version of a 100-kc. oscillator found in The Radio Amateur's Handbook. However, the circuit may be adapted to fit almost any calibrator.

Fig 1
Fig. 1. Diagram of the 100-kc. oscillator with 10 kc markers. Unless otherwise indicated, capacitances are in pF, resistances are in ohm, resistors are ½ watt.

The neon-bulb oscillator is adjusted to oscillate at 10 kc by the potentiometer R1, and its output is coupled to the screen grid of the 6AU6 oscillator by a 30 pF capacitor. The resultant beats of the 10 kc and 100 kc frequencies produce 10 kc markers between the stronger 100 kc points. The neon-bulb oscillator will synchronize or lock in with the 100 kc crystal-controlled oscillator, making this circuit easy to adjust. The oscillator is set by adjusting R1 and listening to the calibrator signals on the station receiver. The 10 kc oscillator may lock in with the 100 kc oscillator at several settings of R1, and the setting that gives the optimum signal strength will have to be found experimentally.

James Bull, W7EIO.