Switch

should be a square wave with a free running frequency of about 150 kHz, This can be checked on the station receiver. The next step is to put the crystal back in the circuit and adjust the trimmer to zero beat with W.W.V, when slightly coupled to the antenna. A /¿L 914 should be used as a buffer amplifier to prevent loading of the oscillator as shown in Fig. 13,

There are several alternatives to consider in place of the /¿L 958 decade dividers if one is not limited by space requirements. One alternative would be to use the basic counter module of Fig, 7A, Another would be to use the minimum hardware type decade divider shown in Fig* 14.

A digital type divider should be used in the time base section as there lias not been as yet developed a reliable, low-component count, regenerative or step type divider that can compare with the digital type for temperature, component tolerancc and frequency stability.

Fig. 15 is the schematic of the complete integrated circuit frequency counter.

The function switch SI selects the mode of measurement. In position 1 check the out put from Q10? the first decade divider, a 3 V P-P pulse is applied to a resistive voltage divider and coupled through a .01 ^F capacitor to the input of the pulse shaper. The level is set at approximately 53 millivolts to allow a setting of the sensitivity control to the most sensitive position for future measurements.

Position 2 "FREQ' is used for most frequency measurements. Some adjustment of the sensitivity control may be needed to handle very small or very large signals. Some consideration should be given the dc level applied to the input jack. The 1 ^F, 50v input capacitor should be changed in the event the unit is used exclusively with tube type circuits. However an external dc block-

COUNTER & DISPLAY LAMPS

TO DISPLAY T!ME

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