Patent GB-717489-A (GB)
Title: Improvements in or relating to radio proximity indicator systems for vehicles
IPC: G01S13/931
Filed: 1952-12-29
Abstract: 717,489. Combined transmitting and receiving systems. NYSTROM, K. G. Dec. 29, 1952 [Dec. 29, 1951], No. 32880/52. Class 40 (5). [Also in Group XXXVIII] In a proximity indicator system for vehicles, e.g. motor cars, each vehicle has a V.H.F. radio transmitter and receiver installed on it alternately energized at a variable rate depending on the operation, for example speed, of the vehicle, so as to avoid synchronism between vehicles, and the transmitter anode circuits are fed with alternating current of variable frequency from power sources on the vehicles and of such waveform, e.g. rectangular, that a wide bandwidth centred round a fixed frequency is obtained in transmitting. In Fig. 6 positive and negative excursions of a rectangular waveform are applied from terminals 6, 7 to the anode circuits of a transmitter T and receiver R, rendering them operative alternately, the waveform being obtained from the secondary of a transformer with earthed centre-tap energized by a generator driven from the vehicle engine or from a D.C. motor supplied from the battery of the vehicle, or by a vibrator operated by the vehicle battery while under charge. In any such case the frequency will therefore vary with the engine speed, and if the waveform is not rectangular it is made so by arranging that the transformer core becomes saturated by, and so limits, the voltage peaks. Pulses received from another vehicle during reception intervals are detected by a grid detector valve V2 and if of sufficient amplitude trigger a thyratron V3 causing an intermittent warning light from an indicator lamp I1. A variable cathode resistor R6 adjusts the threshold bias of the thyratron. In Fig. 9 a mechanical transmit-receive switch S2, S3 is employed operated by a bi-metallic rod Q2 surrounded by a heater coil L12, intermittently operating a switch K3 and energizing a solenoid L13, which acts on an armature Q3 operating the switch S2, S3. In transmit positions K4, K6 of the switch the anode circuit of the valve Vi is supplied with A.C. of rectangular waveform from a terminal 6, and the grid of the valve V1 is connected to earth through a resistor R12. In "receive positions K5, K7, the valve V1 is fed with D.C. anode voltage derived from a full-wave rectifier valve V4 and its grid disconnected from earth so that it acts as a super-regenerative detector of oscillations received from a common transmitting and receiving aerial A. Pulses will be transmitted, about 100 per sec., from the transmitter during positive half cycles in the anode circuit, but the frequency of transmit / receive switching may be only ¢ to 3 cycles per sec. Pulses received from another vehicle dunng intervals of reception will be detected by the valve V1 and applied through a transformer L10 to a thyratron V3, and those that coincide with the positive half cycles of energization of the thyratron anode (some will coincide as their repetition frequency is variable) act to energize intermittently an indicator lamp I1. The system may also be used between fixed beacons and motor cars.