GB619288A - Improvements in beat frequency oscillators - Google Patents

Abstract

619,288. Cathode-ray oscillographs. STANDARD. TELEPHONES & CABLES, Ltd., and GRAYSON, H. Nov. 30, 1946, No. 35537. [Class 37] [Also in Group XL (c)] In a circuit for producing trains of oscillations which start from a constant point in the cycle of oscillation, the outputs of two oscillators are heterodyned to produce a sum or difference output frequency, and one of the oscillators is periodically coerced to oscillate at the frequency of the other, the train starting when this oscillator ceases to be coerced. As shown, the triode portions of the triode-hexodes V1 and V3 are the oscillators, and the hexode portions form a buffer amplifier and a mixer respectively, the output being taken from the mixer through a low-pass filter and a cathode follower stage V4. Oscillator B is periodically coerced to oscillate at the frequency of A by opening a gate valve V2 which feeds the output of A into B, The opening pulse for V2 comes from an external source and is delayed by a valve V6 so that oscillator B may be prepared for coercion by feeding the input pulse in a negative sense to its anode through valve V5, this allowing the free oscillations in B to die away before the coercing oscillations arrive. In a modification, the output of A is fed to B constantly and the presence or absence of the negative pulse on the anode of B determines whether it oscillates at its natural frequency or is coerced into oscillation at the frequency of A. The oscillator may be used for testing video or audio amplifiers in conjunction with a cathode-ray oscillograph, or the associated cathode-ray tube in the case of video amplifier, the controlling pulses being synchronous with the time-base in each case. The oscillator may also be used for calibrating radar sets, the sine wave output being converted to a " pip " waveform and the controlling pulse derived from the transmitter.