Patent GB-972529-A (GB)
Title: Omni-directional altimetric radar
IPC: G01S13/78
Filed: 1961-03-10
Abstract: 972,529. Radio-navigation. STANDARD TELEPHONES & CABLES Ltd. March 20, 1961 [March 16, 1960], No. 8859/61. Addition to 926,921. Heading H4D. In a radio-beacon navigation system in which the beacon transmits omnidirectionally a wave modulated by a reference signal of frequency f1  and by a further signal of frequency f2 (characteristic of a particular beacon) mobile craft (e.g. aircraft) co-operating with the beacon are provided with means for transmitting response signals which, at the beacon, are utilized to produce indications of the range, bearing and altitude of such craft. In one embodiment (Figs. 1 and 2, not shown) for producing the response signals representative of altitude means are provided in the craft for shifting the phase of the reference signal f1 in accordance with the actual altitude of the craft and on coincidence of the pulses of a pulse train derived from this phase-shifted signal with pulses of a pulse train derived from the received signal f2 a signal is derived which initiates the transmission of an altitude representative signal. At the beacon this received signal is employed as a brightening pulse for an altitude display cathode-ray tube, the horizontal deflection of which is produced by a sawtooth wave of frequency f2 and the vertical deflection of which is produced by a sawtooth wave of frequency f1 modified to vary in steps at frequency f2, (f2>f1). In a second embodiment (Fig. 3), for use with a beacon which, additionally, transmits a directive pattern rotating at frequency f1, the equipment on the mobile craft comprises means additional to those described above, for transmitting response signals representative of range and bearing which may be distinguished (at the beacon) from the response signals from other craft " addressed" to other beacons. As shown,the received reference frequency f1 (# 0 ) is supplied to a phase-shifter 74 which is adjusted by the craft altimeter 75 to produce a signal f1[# (h)]representative of the altitude of the craft, this signal being fed as a first input to AND gate 92. A second phase-shifter 71, also supplied with the reference frequency f1 is adjusted via a motor 73 and phase comparator 72 to reduce to zero the phase difference between the reference frequency f1(# 0 ) and the frequency of the rotating directive pattern f1[#(A)] to produce a bearing representative signal which is fed as a first input to a second AND gate 91. As a second input the gates are supplied with respective opposed outputs of a bi-stable flip-flop circuit 95 and therefore alternately supply their first inputs to an OR gate 93, the signal passed by which is converted in generator 57 into a series of pulses 102 and supplied as a first input to OR gate 67 which has as a second input one output of a monostable flip-flop circuit 68. The output from OR gate 67 is supplied as a first input to an AND gate 60 which has as a second input a series of pulses 104 produced in generator 59 from the received distance measuring signal of frequency f2. When a pulse 102 coincides with a pulse 104, gate 60 produces a pulse 114 which, inter alia, is utilized to trigger circuit 68 to its unstable condition and to provide a pulse which, via OR gate 67, holds AND gate 60 open until the next pulse 104 occurs which is passed as pulse 114<SP>1</SP>. In this manner the coincidence of pulses 102 and 104 results in the production of a pair of pulses 114, 114<SP>1</SP> spaced by a period 1/f2 and it is this characteristic which, at the beacon, is utilized to discriminate between responses " addressed " to it and those " addressed " to other beacons. The pairs of pulses 114, 114<SP>1</SP> are fed as a first input to three AND gates 94, 96 and 97, gate 94 receiving as a second input the " stable " output of circuit 68 so that only pulses 114 are passed and these pulses are employed to switch the bi-stable circuit 95 between its two states which in addition to supplying the first inputs to gates 91, 92 provides the second inputs to AND gates 96, 97. The latter therefore conduct alternately and supply the pulse pairs 114, 114<SP>1</SP> to coders 64, 65 which convert each of the input pulses into a pair of pulses those from coder 64 being spaced by a factor # (h) characteristic of the altitude of the craft and those from coder 65 by a factor # (A) characteristic of the azimuthal bearing of the craft. These pulse pairs are then transmitted alternately and at the beacon the pulse pairs from coder 64 are utilized to provide an indication of the distance and altitude of the craft whilst the pulse pairs from coder 65 provide an indication of the bearing of the craft with respect to the beacon.