Patent GB-595074-A (GB)
Title: Improvement in radio direction finding
IPC: G01S3/10
Filed: 1944-12-12
Abstract: 595,074. Radio direction-finding. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Dec. 12, 1944, No. 24947. Convention date, Aug. 28, 1942. [Class 40 (v)] Relates to the provision of means in direction finders receiving telegraphic-like signals for eliminating night effect by utilizing the first portion only of each signal. According to the invention, in a direction finder of the kind including two mutually perpendicular directional aerials connected through separate channels to the perpendicular deflection systems of a cathode-ray tube and an omni-directional sense aerial connected through another channel to the brilliancy control electrode of the cathode-ray tube, the two directional channels are normally biassed to cut-off, the biasses being removed during the first portion of each received signal or the two channels are normally conductive and are biassed to cut-off by biasses initiated and terminated respectively by pulses derived with a slight delay from the leading and trailing edges of the received signals, The invention is described as applied to a two-path direction finder, Fig. 1, with a crossed Adcock array N-S, E-W in which an auxiliary aerial R is located a short distance from and on a, line bisecting the diagonals of the array, a signal from a local oscillator 11 differing slightly in frequency from the incoming signal being radiated from the auxiliary aerial.. The combined incoming and locally generated signals are picked up by the array and the two components are fed through separate superheterodyne receivers 5, 15 and 7, 17 having a common local oscillator 13, the beat-frequency outputs being applied through the normally biassed-off amplifiers 23 and 27 to the deflection plates of the cathode-ray tube indicator 25. The signals received on the central sense aerial C are applied through a separate receiver 9, 19 to black out half the cathode-ray trace to eliminate the 180 degrees ambiguity. The receiver 9 is provided with a duplicate detector 21 and the output from this, Fig. 2a, is differentiated by the C.R. circuit 41, 43 to give a peaky waveform, Fig. 2b, the negative peaks being suppressed by the diode 45. The resultant positive pulses, Fig. 2c, are further differentiated by the circuit comprising condenser 49 and the grid-to-cathode resistance of the normally conductive triode 47 which is cut off by the negative pulse, Fig. 2d, for a time determined by the setting of the variable resistance 53 connecting the grid to H.T. +, and the positive pulse, Fig. 2e, produced in the anode circuit is fed to unblock amplifiers 23, 27 so that the indication on the cathode-ray tube is produced by the first component only of the signal. In a modification, Fig. 3 (not shown), the amplifiers are blocked shortly after receipt of a signal as above, but they are unblocked shortly after the termination of the signal and remain unblocked until the succeeding signal is received. This is achieved by duplicating the circuits 21 to 47 and reversing the connections of duplicate diodes 21 and 39 to produce negative signals corresponding to the positive signals, Fig. 2a, in the original circuit. Thus, two short rectangular pulses corresponding to Fig. 2b are produced, their leading edges being coincident with the commencement and termination respectively of the signal and these pulses are further differentiated and the sharp pulses coincident with their trailing edges are applied to trigger a D.C. coupled multivibrator which produces a positive rectangular pulse for unblocking the amplifiers 23 and 27. Specification 520,606 is referred to.