GB628862A - Improvements in transmitting-receiving circuits for short waves - Google Patents

Abstract

628,862. Radio receiving systems. PHILIPS LAMPS, Ltd. March 26, 1947, No. 8236. Convention date, July 28, 1944. Addition to 623,069. [Classes 40 (v) and 40 (vi)] [Also in Group XXXVIII] In a radio transceiver circuit of the type described in the parent Specification, means are provided to change over the circuit automatically from transmission to reception, and conversely. Incoming oscillations are applied in push-pull to mixing valves 3<1> and 3<11>, and local oscillations are generated in parallel phase by these valves, as described in the parent Specification, so that an intermediate frequency output is obtained from timed circuit 12, 13. For transmitting purposes, valves 3<1> and 3<11> generate oscillations in push-pull in tuned circuit 2<1>, 2<11> which consists of Lecher lines, for transmission from aerial 1<1>, 1<11>. The push-pull oscillations for transmission are produced by means of the positive feed-back provided by inductances 14<1> and 14<11> in conjunction with the anode-grid capacities, and the parallel phase oscillations for heterodyne reception are produced by means of the positive feed-back provided by inductance 15. The parallel phase circuit consisting of impedance 5, the parallel connected impedances of both halves of the push-pull circuit and variable impedance 16 is tuned to the frequency of the local oscillations. This tuned circuit may be periodically damped under the control of diode 22 which shunts impedance 5, to prevent the production of parallel phase oscillations, the circuit then operating as a transmitter. On removal of the damping, the local oscillations are produced and the circuit operates as a superheterodyne receiver. Diode 22 is normally held non- conducting by the current through the cathode load 21 of valve 19. If a modulating signal is applied to the grid of valve 19, the valve current decreases, due to rectification effect, and diode 22 becomes conductive, thereby damping the parallel phase oscillating circuit. Instead of utilizing the modulating signal to effect the switching control, an oscillation at supersonic frequency may be applied to valve 19, to continuously switch the circuit between the states of transmission and reception. This switching frequency may also be received by the distant co-operating transmitting receiving station, where it is used to effect a corresponding switching control. The phase of this control frequency at the distant station, and also the value of the frequency at the main station, may be adjusted to allow for transit time effects and ensure effective synchronism between the co-operating transmitting and receiving periods at the two stations. The arrangement may be extended to a plurality of stations and several different switching frequencies may be used.