The Franklin Oscillator Circuit

A separate phase inverter tube is used in this oscillator to feed a portion of the output back to the input in the proper phase to sustain oscillation. The values of Cj and C2 should be as small as will permit oscillations to be sustained over the desired frequency range.

V.F.O. Transmit- When used to control the fre-

ter Controls quency of a transmitter in which there are stringent limitations on frequency tolerance, several precautions are taken to ensure that a variable frequency oscillator will stay on frequency. The oscillator is fed from a voltage regulated power supply, uses a well designed and temperature compensated tank circuit, is of rugged mechanical construction to avoid the effects of shock and vibration, is protected against excessive changes in ambient room temperature, and is isolated from feedback or stray coupling from other portions of the transmitter by shielding, filtering of voltage supply leads, and incorporation of one or more buffer-ampli-fier stages. In a high power transmitter a small amount of stray coupling from the final amplifier to the oscillator can produce appreciable degradation of the oscillator stability if both are on the same frequency. Therefore, the oscillator usually is operated on a subharmonic of the transmitter output frequency, with one or more frequency multipliers between the oscillator and final amplifier.

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