Patent GB-635277-A (GB)
Title: Improvements in or relating to radio direction finders
IPC: G01S3/54
Filed: 1947-03-11
Abstract: 635,277. Radio direction-finders. STANDARD TELEPHONES & CABLES, Ltd., and EARP, C. W. March 11, 1947, No. 6714. [Class 40 (vii)] A radio direction-finder comprises two perpendicularly-arranged linear aerial-arrays, the aerials of each array being coupled in succession to respective receiving circuits, one for each array, whereby the received signal from each array bears a phase-modulation corresponding to the direction of reception of the received radio signal, and means for phase-discriminating the received signals to yield two lowfrequency signals, which are applied to the deflecting plates of a cathode-ray tube to deflect the spot thereof in a direction corresponding to the direction of reception. The two sets of aerials 1, 2, 3, 4 and A, B, C, D are situated at positions on the perpendicular lines 5, 6 determined by projection from the apices 8 ... 15 of a regular octagon, as shown in Fig. 1. The aerials may comprise vertical elements for receiving vertically-polarized radiation or they may comprise pairs of crossed elements, feeding in quadrature, for receiving horizontally - polarized radiation. Switching waveforms generated in the units 16 and 17, Fig. 3, and having frequencies F1 and F2 respectively cause the aerials of the array 1, 2, 3, 4 to be coupled to the receiver 18, Fig. 4, in the order 1, 2, 3, 4, 3, 2, 1, and cause the aerials A, B, C, D to be coupled to receiver 19 in the order A, B, C, D, C, B, A, the duration. of each period of application of the aerials 1, 4, A and D being twice as long as that for the remaining aerials. The signals received in receivers 18 and 19 are consequently substantially sinusoidally phase-modulated to an extent proportional to cos # and sin # respectively (see Fig. 1). The output of receiver 19 is frequency-changed at 24, 20 being a local oscillator, amplified at 28 and again frequencychanged at 30, 31 being a crystal-controlled oscillator. The output from the frequencychanger 30 is amplified at 33 and applied to a further frequency-changer 36 to which is also applied the signal from the receiver 18 after frequency-changing at 23 and amplification at 38. The output from the frequency-changer 36 consequently comprises a signal of the frequency of the oscillator 31 phase-modulated by the difference between the phase-modulations of the signals received by the two aerial arrays. The output from 36 is amplified at 41, Fig. 3, and applied to phase-discriminator 43, the output from which is applied to bandpass filter 45 passing the fundamental frequencies of the switching frequencies F1 and F2 only. The output of filter 45 is applied in series to the primary windings of the transformers 53 and 54. Signals of frequency F1 and F2 from the units 16 and 17 are applied to centre-tappings on the secondary windings of the transformers 53 and 54 respectively. These secondaries are coupled via rectifiers 59, 60, 61, 62 to the deflecting plates of a cathode-ray tube to the horizontally-deflecting plates of which a steady voltage corresponding to the amplitude of. the signal of frequency F2 from the filter 45 is applied, and to the verticallydeflecting plates of which a steady voltage corresponding in amplitude to the signal of frequency F1 is applied. The spot on the cathode-ray tube is consequently deflected in accordance with the direction of reception of the received signal; means may be provided for converting the spot deflection into a radial line as described in Specification 590,260, [Group XXXVI]. Specification 594,530 also is referred to.