Patent GB-580361-A (GB)
Title: Improvements in or relating to radio direction finders
IPC: G01S1/02
Filed: 1942-08-06
Abstract: 580,361. Wireless directionfinding systems. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). Aug. 6, 1942, No. 10973. [Class 40 (v)] A direct-reading cathode-ray oscilloscope radio direction-finder comprises a rotatable directional antenna system, means synchronised by the output thereof for combining the energy received from a non-directional antenna with that received by the rotatable system for brief intervals of time at the maxima of the output from the latter, and means controlled by the combined output for suppressing the indicating diagram on the screen of the oscilloscope during one indication of direction in each cycle of rotation of the directional system, so removing the 180 degrees directional ambiguity produced by the double indication otherwise obtained. The suppression may be effected by extinguishing the spot, or by blocking the application of signals from the directional antenna system to the oscilloscope deflection circuits, for the required period. In the system shown in Fig. 2, a motor M rotates a directional loop antenna LA and the magnetic deflecting system N of an oscilloscope indicator. The signals picked up by the loop and modulated at the rotation frequency are amplified in R, detected in D and the resulting uni-directional half-wave signals are applied through a limiter K to the coil N, whereby in known manner a bearing indication of the form t1, t2 shown in Fig. 5 would be obtained on the oscillograph screen were no means provided to eliminate the portion t2, which indicates a bearing 180 degrees displaced from the true direction. To eliminate this portion, signals from a non-directional aerial A are passed to a normally blocked amplifier P, which is periodically unblocked for short periods by square-topped impulses supplied from a circuit Z and derived from a saw-tooth wave. During these periods, signals from the aerial A pass to the amplifier R and are combined with the unidirectional half-wave output from the detector D. This occurs only at the maximum of alternate half-waves occurring when the signals are in phase, since the tube producing the saw-tooth oscillation is triggered only when these maxima are increased by the combination of the signals. The combined output from the detector D is applied to a limiter circuit V which passes the detector output only during the periods of increased maxima to a time-constant circuit G. This supplies at each actuation a cut-off bias to the oscilloscope lasting at least for a half cycle of the curve A, so that the beam is cut-off from point U to point U1, curve E, eliminating the bearing indication t2 which gives the incorrect sense. In a similar system, Fig. 8 (not shown), blocking voltages similarly derived are applied to a detector or subsequent low-frequency stage by which the combined signals from the two aerials are supplied to the oscillograph deflecting system, so that the spot, though not extinguished, is not deflected during the period when the trace t2 would occur. In a modification, Fig. 9 (not shown), in which the signals are supplied to distantly-located oscillograph indicators, the output of a high-frequency transmitter is modulated by the signals and is cut off during the periods when the indication is to be suppressed. The transmitter output is supplied to a two-phase distributer (e.g. to the rotatable coil of a goniometer) which is rotated in synchronism with the aerial goniometor. The two-phase output from the distributer is supplied over transmission lines to distantly-located receivers to which the oscillographs are connected. In the system shown in Fig. 10, the bearing indications are produced in known manner by the application to the two pairs of deflection plates in the oscilloscope of voltages in phase quadrature derived from a rotary potentialdivider 8 which is rotated synchronously with the movable coil of an aerial goniometer 2 and is connected to a receiver 3, the output diode 11 of which supplies the signals to a valve 7 in the anode circuit of which the potentiometer is included. A voltage divider 17 in parallel with the load resistance 12 of the diode 11 applies the detected signals, which are in the form of unidirectional half-waves, via an amplifier valve 18 to a gas-filled valve 19, to which is connected a relaxation circuit 21, 22, thus causing it to discharge at the signal peaks. Each discharge causes momentary operation of the tube 24, of which the grid is normally biassed to cut-off point, and which receives, after suitable phase displacement, the signals from a non-directional aerial. During the operative periods of the tube 24, the signals pass via a condenser 26 to the receiver 3, where they are added to those from the goniometer. The voltage divider 17 applies the same signals to the valve 28 which triggers a gas-filled valve 29 only at the peaks produced by the addition of the in-phase signals from both aerials, that is at each alternate half-wave of the detected signals. This, through a valve 32 and air-core transformer 33, causes a cut-off voltage to be applied to the grid 16 of the oscilloscope for a period depending on the timeconstant of output circuit of the valve 32, during which period the undesired part of the diagram on the oscilloscope screen is eliminated owing to extinction of the beam. To secure regular operation of the gas-filled valves 19, 29 with input signals of varying strength,'their grids are connected to the plate circuit of a second diode rectifier 39 to which the signals are applied by a condenser 38. The rectified current produces a negative bias increasing with signal strength. Modifications of this circuit are illustrated in which (a) the valve 23 is omitted, (b) the valve 32 is omitted, (c) the valve 32 is connected to the grid of the oscilloscope by a condenser in place of a transformer, (d) resistance-capacity networks are provided which produce on the grid of the oscilloscope a counter-bias to that produced on it by selfpolarization due to the asymmetrical signals, (e) the output from the transformer 33 is applied, not to the oscilloscope, but to a circuit producing a cut-off bias on the grid of the valve 7 during the periods when the trace is to be eliminated. Specifications 519,351. and 24521 /39, as open to inspection under Sect. 91, are referred to.