The field effect transistors have characteristics that allow the realization of excellent oscillators, as shown in the figure, which operates from 4 to 18MHz. The transistor used is a junction FET, like the BF245 or MPF102, and there is no tuned tank circuit. The RF shock must have an impedance high enough at the resonance frequency of the crystal to allow the signal to pass to the output. The crystal is of the fundamental type and the output signal will vary in intensity depending on the frequency. The current consumption of this circuit is quite low, less than 10 mA, and if there is little efficiency, the inversion of terminals D and S may be suspected.
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