Patent GB-596794-A (GB)
Title: Radio locating and communicating systems
IPC: G01S7/282
Filed: 1945-01-05
Abstract: 596,794. Radio signalling. STANDARD TELEPHONES & CABLES, Ltd. Jan. 5, 1945, No. 561. Convention date, Jan. 8, 1944. Addition to 590,701. [Class 40 (v)] A transmitter receiver for a pulse communication. system comprises a selfpulsing oscillator which for reception is triggerable by incoming pulses ahead of its normal pulsing period and for transmission has its pulsing rate controlled by signals, a transmitreceiver switch rendering the pulsing of the oscillator insensitive to incoming pulses during transmission, and during reception causing the received pulses to control the triggering of the oscillator and thus reproduce the intelligence on the received pulses. In the combined radar and communication system of Fig. 1, the ground station 10 comprises the squegging oscillator 15, pulses being radiated from aerial 14. The pulse recurrence frequency is controlled by the time constant of the grid condenser 22 and resistor 23 and the bias applied over resistors 36, 37. For the transmitting function a negative bias is applied over switch 38 and the triggering of the oscillator is controlled over switch 40 by signal impulses from a system 60. The sawtooth grid voltage wave of the oscillator is clipped in circuit 48 to provide the sweep voltage for the oscilloscope 46, on which are displayed echo pulses such as 12a from a craft 12, which are received by aerial 44 and receiver 43. The receiver is normally blocked by voltage from a source 54 but is unblocked for the desired interval following each transmitted pulse by a square wave obtained by limiting and shaping the oscillator grid voltage in circuit 56. The impulse generating and modulating system 60 is of the " cusper " type. An alternating wave 66 and the output from amplifier 63 produced by microphone 61 are fed to the full-wave rectifier comprising valves 71, 72 via transformer 67, in such a manner that the rectified wave 69 is produced. The positions of the cusps 82a, 82b are controlled by the differing bias voltage sources 75, 76 and the speech voltage, and the rectifier output is clipped and amplified at 84 to produce the impulses 42a, b, which are fed over switch 40 control the triggering of the transmitter. The craft, with which communication is to be obtained, carries a transmitter-receiver 13, Fig. 3 (not shown), which is substantially identical with the oscillator and modulator of Fig. 1. and operates to transmit and receive in the same fashion. In order to receive time modulated pulses on the ground equipment, Fig. 1, the switches 38, 40 are changed over to remove the source of triggering pulses from the oscillator and to provide zero bias which lowers its triggering level. Pulses 52a, b, &c., Fig. 4, which are received by the aerial 14 then trigger the oscillator circuit when they exceed the triggering level 41b in the grid circuit. Pulses 92a, b, &c. are thus produced in the oscillator anode circuit, which reproduce the time modulation of the received pulses, and are fed to a harmonic generator 32 and demodulator 33 in the demodulator unit 31, which is illustrated in detail in Fig. 3 (not shown). The demodulator comprises a valve 93 which is fed on the control grid with the amplified pulses 92a, b, &c. while its screen grid is fed through a phaseshifting network with the output from the tuned circuit of the harmonic generator which is shock excited into resonance at a harmonic 112 of the average pulse recurrence frequency. The bias of the demodulator valve is selected to provide a threshold clipping level 114 so that the demodulator output pulses 93a, b, &c. are of amplitude dependent upon the relative timing of the pulse and harmonic wave. The envelope 115 of the output pulses, which reproduces the original modulation, is removed by a filter and passed to headphones.