Patent GB-764822-A (GB)
Title: Improvements in and relating to systems for automatic radio direction finding
IPC: G01S13/86
Filed: 1953-09-21
Abstract: 764,822. Radar SVENSKA AKTIEBOLAGET GASACCUMULATOR. Sept. 21, 1953 [Oct. 27, 1952], No. 25969/53. Class 40(7) A radio direction finder and a separate radar, viewing the same field have a common indicator which is scanned synchronously with the radar scanning, the direction finder being provided with means for storing an indication of the bearing angle until the radar aerial is scanning in a direction corresponding thereto when a signal is provided for making an indication. It is therefore unnecessary for the direction finder and radar aerial scans to be synchronized. In one embodiment a narrow beam direction finder aerial 10 is rotated by motor 12 and the signal received when it is directed towards a transmitter is passed over slip rings 14 and 15 to receiver 13 coupled to timing device 21 which delivers an output pulse through relay winding 39 at a time corresponding to the received pulse. Relay 39 is provided with holding contacts 40 and an armature 38 pressing a brake shoe 37 against the rim of disc 33. Thus on passage of a pulse through relay coil 39 shoe 37 contacts the rim of disc 33 which is normally driven by gearing 23, 24 and selsyn system 26 and 31 in synchronism with the aerial rotation. Due to the action of a spring loaded device disc 33 is stopped by the brake although the aerial and the disc drive continue to rotate. The effect of stopping the disc is to " store" information about the direction from which the signal has been received in terms of the angular position of contacts on the disc surface. The information is stored in this way until the aerial 10 passes through a reference direction when a pulse of energy is fed over contacts 60 and 61 to cause the relay magnet to be demagnetized whereupon the holding contacts 40 are released and so is the brake shoe 37 allowing the disc to return rapidly to its normal angular relationship with its drive under the influence of the spring loaded device. The radar comprises a directive aerial 29 constantly rotated by motor 28 at a speed preferably rather slower than the speed of rotation of aerial 10 and the transmitter-receiver equipment 48 from which signals corresponding to returned pulses are fed to modulate cathode-ray tube indicator 22. The rotation of the aerial and the scanning of the indicator are synchronized by means of drive 44, 45, selsyn system 50, 52 and drive 55, 56. Coupled to the selsyn system is a second receiver 51 which rotates an arm carrying leads 35 and 36 extending to contacts which press against the surface of the disc 33. When the direction of the radar aerial corresponds to the bearing information stored by the disc 33 the contacts on the disc surface bridge the arm contacts and current flows over lead 59 to cause a radial bearing indication line to be drawn on the indicator screen. If preferred other ways of marking the bearing indication on the indicator may be used, for example two radial lines forming a narrow angle between them' may enclose the bearing direction. An alternative arrangement is described with reference to Figs 2 and 3 (not shown) in which the mechanical storage unit involving disc .33 is replaced by an electronic arrangement comprising a binary counter receiving a pulse each time the antenna 10 moves through 1 degree from the reference direction until the output of circuit 21 cuts off any further supply of pulses and a second counter is similarly fed by 1 degree pulses with respect to the movement of aerial 29. The counters are reset each time their corresponding aerial passes through zero and a co-incidence circuit is provided which releases an output signal when the counters register the same value to cause the bearing marker signal to appear on the indicator. In this arrangement the duration of the direction finding pulse may be allowed for by feeding every other 1 degree pulse to the direction-finder counter for the duration of the pulse. The angular information stored thus coresponds to the angular separation between reference direction and the direction corresponding to the mid point of the direction-finder pulse.