GB858114A - Improvements in or relating to polyphase oscillator and like circuits - Google Patents

Abstract

858,114. Valve oscillator and amplifier circuits; phase and frequency modulation. SALAM, H. P. A. Feb. 7, 1957 [Feb. 7, 1956], No. 3841/56. Classes 40(5) and 40(6). A circuit for producing two or three phase oscillations, for producing a phase modulated signal or for converting amplitude modulated wave to phase modulated wave comprises two frequency selective amplifiers and a source of oscillation of the centre frequency of the selective amplifiers the input to each amplifier being obtained by combining in a symmetrical T-network the output of the other amplifier and the source. Fig. 3 shows an oscillator comprising three amplifiers having tuned anode circuits, the output from each pair being combined in a T- network C1, C2 and fed to the input of the third amplifier. When the circuits are identical three phase oscillations are produced but when the output amplitude of one is less than the others the two equal amplitude oscillations are in phase quadrature and thus two phase oscillations are produced. In an alternative oscillator (Fig. 4) the amplifiers have frequency selective input circuits formed by the frequency selective arms of a Wien bridge (Fig. 5) and the T-networks coupling the outputs to the inputs are resistive and comprise resistors R3, R4. Lamps or thermistors I limit the amplitude of oscillation. Alternatively peak limiting diodes in the anode or screen circuits may be used for this purpose in both Figs. 3 and 4. One of the amplifiers may be replaced by an external source of oscillation (Fig. 2, not shown) in which case two or three or other phase related oscillations may be obtained from the circuit according to the amplitude of the external oscillation. If the external oscillation is amplitude modulated, phase modulated oscillations will be produced in the circuit. Alternatively phase modulated oscillations may be produced by this arrangement by having a constant value of external oscillation and modulating the output from one of the amplifiers. For example, in Fig. 6 which comprises two amplifiers V and a third source of oscillations XY the output from the left-hand amplifier is modulated by a source MI through a circuit RpT and a diode rectifier. If the modulation is suitably integrated before being applied to the transformer a frequency modulated oscillation is produced. Alternatively direct frequency modulations can be achieved using the three phase oscillator circuit of Fig. 3 in conjunction with a balanced modulator. It is suggested that grounded emitter transistors could be used in the circuit, operating under class c conditions where power efficiency is required.