A Low-Frequency Crystal Controlled Oscillator

The RF engineer sometimes has to look for an instrument that will check a low frequency quartz crystal unit reliably and rapidly. This is a difficult piece of equipment to find and the engineer often has to consult an electronic circuits handbook for the schematic of a circuit that will perform the task.

Unfortunately, there aren't many such circuits in the technical literature currently available, and when found, they don't always work as expected. A circuit that has been found to work at full satisfaction in the frequency range from 10 kHz to 500 kHz is illustrated in follow.

This is a schematic of a low frequency sine wave oscillator featuring low distortion, wideband operation and crystal control.The circuit, originally developed for laboratory use, employs low cost AF bipolar transistors for the oscillator and amplifier sections and a JFET for loop-gain control. Operation of the oscillator in the 10 kHz to 500 kHz frequency range has been found to be excellent, while measured distortion is kept under 0.1 percent.
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