Patent GB-678148-A (GB)
Title: Improvements in or relating to radio direction finders
Inventor: EARP CHARLES WILLIAM
IPC: G01S3/54
Filed: 1947-03-26
Abstract: 678,148. Radio direction-finders. STANDARD TELEPHONES & CABLES, Ltd. March 25, 1948 [March 26, 1947], No. 8217/47. Class 40 (vii). In a radio direction-finder, the signals from a plurality of aerials are commutatively switched to a single receiver in such a manner as to derive two interlocking signal trains, at least one train being phase-modulated in accordance with the direction of the incoming signals, and the output from the receiver is fed alternately, in synchronism with the commutative switching, to two separate channels, the signals derived from which are applied, either separately or in combination, to an indicating circuit for indicating the direction of the incoming signals. The invention may be used for direction-finding upon incoherent signal trains; in such an arrangement two separate signals are applied on a time-sharing basis to the receiver and by a comparison of the phases thereof a further signal is derived which is phase-modulated in a manner indicative of the direction of the incoming signals and is independent of any incoherence thereof. The system illustrated in Fig. 1 comprises an odd number, e.g. nine, of aerials, which are equally spaced around the circumference of a circle. The aerials are coupled over normally blocked amplifiers to the receiver 19. Switching pulses from a 9-phase pulse generator 33, of the tupe described in Specification 596,699, are applied in succession to the amplifiers so that the aerials are connected to the receiver in the order a, f, b, g, c, h, d, i, e, a, &c., i.e. successively connected aerials are approximately oppositely situated around the circle. The receiver output which is at an intermediate frequency, is amplified at 39 whence it is passed via detector and amplifier 74 and filter 76 to loud-speaker 78 whereby any message intelligence in the received signal is extracted. The output of amplifier 39 is also applied to the amplifier 40 and frequency-changer 42 which are switched on alternately in synchronism with the aerial switching by a switching signal from the unit 88. These switching pulses B, Fig. 2, are derived, by frequency-division by two, from the output A of 1000 c/s. pulse generator 30 which is also coupled to the 9-phase generator 33, one phase of which is illustrated at C. The signal applied to unit 42 is combined with the output of stable 50 kc/s. oscillator 44, so that the output signal is changed in frequency by 50 kc/s. This signal and the corresponding output of amplifier 40 are applied to respective filter and delay circuits 51, 49, having delays of one millisecond each. (The circuits 51, 49 may also effect broadening of the pulses applied thereto.) The output signals from units 40, 42, 49 and 51 are applied as shown to frequency changers 54 and 57, the outputs of which comprise alternately occurring 50 kc/s. signals due to the heterodyning of the directly transmitted and delayed pulses. The signals from the frequency-changers are combined and applied through 50 kc/s. filter 60 to phase-discriminator 62, the output of which is applied, through filter 64, to phase comparator 66. The output of the discriminator 62, owing to the switching arrangements used, is similar to that obtained by successively switching the aerials of an 18 aerial array into a single channel. The input to the phase-comparator 66 is consequently a 55.55 c/s. signal which is compared with a further signal of the same frequency derived from the pulse generator 30. The 500 c/s. square-wave output of the frequency-divider 88, B, Fig. 2, is mixed with an output, e.g. C, of the generator 33 to derive a resultant signal D which is limited at 67, the output of which is as shown at E, and is then passed through a lowpass filter 71, the output of which is applied to the phase-comparator for comparison with the output of discriminator 62. In a further embodiment, Fig. 3 (not shown), the two perpendicular arrays of successivelyselected aerials are applied alternately to the receiver. The signals from the two arrays are separated from one another at the output of the receiver and by passing them through a narrowband filter the gaps between successive components of each signal are at least partially removed. These signals are discriminated separately and the discriminated signals are used to provide the bearing information on an indicator. Alternately if the two signals are phase-modulated at different fundamental rates they may be combined and a single phasediscriminator used as described in Specification 635,277. In the arrangement of Fig. 4, the successively selected aerials of the circular array 103 ... 108 are alternated with the aerial 109, i.e. the aerials are selected in the order 103, 109, 104, 109, 105, &c. Specifications 594,530 and 638,292 also are referred to.