Patent GB-600794-A (GB)
Title: Radio direction- indicating device
IPC: G01S1/02
Filed: 1945-08-21
Abstract: 600,794. Radio navigation. HAZELTINE CORPORATION. Aug. 21, 1945, No. 21410. Convention date, Sept. 15, 1944. [Classes 40 (vi) and 40 (vii)] Relates to pulse radio navigation systems for determining the bearing of a source of pulses by means of spaced receiving aerials or for determining the bearing of a single receiving aerial with respect to spaced aerials transmitting pulses in a predetermined phase relationship. In either case, the time interval between the reception of two corresponding pulses is proportional to d sin a, where d is the distance between the two spaced aerials and is assumed to be small compared to the distance between the transmitter and receiver and a is the bearing referred to the perpendicular bisector of the two aerials. According to the invention, the bearing is determined by deriving a control pulse having a duration equal to the time interval. The invention is described as applied to a system with spaced transmitters triggered by a local modulator, but in a modification the transmitters function as responders being triggered by pulses radiated from a mobile equipment. Fig. 1 shows four transmitters 13, 14, 18, 19 modulated simultaneously by pulses from the generator 15 and radiating at different carrier frequencies from the aerials 11, 12, 16, 17 which are spaced in the four quarters N, S, E and W. The signals from aerials 11 and 12 are picked up by a mobile receiver and fed through the separate RF and IF channels 21-23 and 21<1>-23<1> to the diode detectors 30 and 30<1> which have long time-constant parallel R.C. loads 31, 32 and 31', 32<1> such that a pulse signal, Fig. 2A, produces a step voltage B with a slow exponential decay. The detector outputs are differentially connected in series between the grids of the valves 36, 36<1> which are conductive in the absence of signals. If the receiver is in the NE or NW quadrants, the signal from aerial 11 is received first and produces a step voltage, Fig. 2c, which is negative at the grid of valve 36<1>, the succeeding pulse D from aerial 12 producing a positive waveform E so that the resultant input to valve 36<1> is a negative pulse F of duration equal to the time interval between pulses A and D. Since the anode of valve 36<1> is connected to H.T.+ by a high resistance 38<1> and to earth by the capacitor 37<1>, the pulse F produces a positive saw-tooth voltage 9, the amplitude of which is proportional to the duration of pulse F and this voltage is applied to the upper Y plate of the cathode-ray tube 42 through a cathode follower 391 with a long time-constant parallel R.C. cathode circuit 40<1>, 411 which gives a substantially constant positive D.C. voltage H of amplitude proportional to the peak of the saw-tooth 9. The cathode-ray beam is thus deflected upwards by an. amount proportional to d sin a, but if the receiver is in the SE or SW quadrants the signal from aerial 12 is received first and the valves 30, 36 and 39 produce a similar voltage which is applied to the lower Y plate to deflect the beam downwards. The signals from E-W aerials 16, 17 are fed through similar circuits 43 and 44 to give a voltage proportional to d cos a which is applied to the X plates so that the angular position of the spot on the screen indicates the bearing angle a.