Patent GB-740362-A (GB)
Title: Arrangements in automatic radio direction finding systems
IPC: G01S7/292
Filed: 1952-08-27
Abstract: 740,362. Radio direction-finding. SVENSKA AKTIEBOLAGET GASACCUMULATOR. Aug. 27, 1952 [Sept. 1, 1951], No. 21529/52. Class 40 (7). A constantly rotating narrow beam directionfinding system includes a cathode-ray tube indicator in which a field is created which rotates in synchronism with the aerial beam and which is supplied with a sharp marking pulse independent of the width of the signal pulse applied to the receiver from the aerial system. The marking pulse is applied to the indicator a predetermined constant delay time after the time when half the signal pulse has elapsed, this latter time being evaluated by the delay means as the mean of the times at which the signal pulse begins and ends. In one embodiment the directive aerial system 10 is rotated by motor 12 and the cathode-ray tube deflection coil system 21 is rotated in synchronism by the mechanical linkage 16, 17, 18 and 19. Signals from the aerial system are passed to receiver 14 whose output may be fed directly to the tube to give a radial lobe pattern over lines 28 although such connection forms no part of the invention. According to the invention the receiver output pulse is applied over line 29 and valve 30 to quick-acting relay 31 which is operated substantially for the whole pulse duration. The normally open contact 32 of the relay is then closed and completes a circuit energizing magnetic clutch 34 and so applying a drive over shaft 40 and gear-wheel 41 to timing disc 42. This disc, therefore, is driven over the mechanical connections shown for the duration of the signal pulse. When the signal pulse ceases relay 31 is de-energized and completes an energizing circuit for relay 50 which closes, thereby energizing relay 47 which breaks the circuit of relay 50 at 46 and completes its own holding circuit at 55. It also closes contacts 56 in the circuit of magnetic clutch 58 causing the disc 42 to continue to be driven in the same direction but by gear 59. It is driven until projection 60 operates limit switch 53, breaking the holding circuit of relay 47 and at the same instant applying a brief marking pulse over line 61 to the cathode-ray tube indicator. Immediately relay 47 opens clutch 58 releases and spring 62 returns the disc 42 to its initial position with projection 60 against stop 63. It is then ready for a further operation. The gearing is arranged so that when the drive is through clutch 34 the disc 42 rotates at only half of the speed of rotation when the drive is through clutch 58. Thus whatever the signal pulse width the marking pulse occurs a fixed delay after its mid-point. This fixed delay is allowed for in the calibration of the indicator device. To prevent operation by short spurious pulses the coil of relay 50 is shorted out over cam-operated contacts 64 until the disc 42 has moved through an angle short of, but approaching, that due to the reception of a normal length signal. Modifications of the timing arrangements are described with reference to Figs. 4, 5 and 6 (all not shown). These avoid the necessity of having rotating parts and in the first of these relays are used to control the charging of a condenser. This is done at a certain rate for the duration of the signal pulse and thereafter at double the rate until a predetermined total charge is reached. The marker pulse is then transmitted to the indicator and the circuit reset. The second arrangement comprises a circuit without relays which is entirely valveoperated but which depends in the same way on the charging of a condenser at half and full rate. The third arrangement makes use of a control oscillator and electronic counter circuits. The latter count half the number of pulses from the control oscillator for the duration of the signal pulse and then all subsequent pulses until a predetermined number is reached. The marking pulse is then formed and the counters reset. In each of these modifications arrangements are provided for preventing the production of a marker pulse after a short spurious signal pulse and for resetting the timing circuit to zero immediately such a pulse has ended.