Patent GB-635487-A (GB)
Title: Improvements in or relating to radio navigation systems
IPC: G01S1/24
Filed: 1946-10-02
Abstract: 635,487. Radio navigation. STANDARD TELEPHONES & CABLES, Ltd., and STRONG, C. E. Oct. 2, 1946, No. 29361. [Class 40 (vii)] [Also in Group XL (b)] A beacon station for radio navigation comprises an array of at least three aerials equally spaced around the circumference of a circle, an aerial located at the centre of the circle, means for transmitting, as a bearing signal, consecutive equi-spaced pulses from consecutive aerials of the array, means for transmitting from the central aerial, as a reference signal, a series of pulses so relatively timed and interleaved with the equi-spaced pulses as to vary cyclically in relative timing in the same manner as the equi-spaced pulses at a distant point in a given direction and means for transmitting from the central transmitter synchronizing pulses of distinctive characteristic. As shown in Fig. 1, the beacon station comprises an array of four omnidirectional aerials 1 ... 4, equally spaced around the circumference of a circle of 600 metres diameter, together with another aerial 5 located at the centre of the circle, each aerial being energized by radio transmitter means 11 controlled by pulse amplifiers 12. These amplifiers are supplied with pulse energy from a 6-channel multiphase transmitter 16 which supplies, at terminal points 18, 19 and 21 respectively, pulses which may be time-modulated in 23, 24, 25 by information consisting of a call sign, ranging tone and traffic signals and, from terminal points 17, 20 and 22 unmodulated pulses for synchronization, reference and bearing. The synchronizing pulses have a greater amplitude and duration (2 Á/sec.) than the other channel pulses (0.5 Á/sec.) so as to have a good signal-to-noise ratio for satisfactory operation of the associated receiving apparatus. The unmodulated pulses from terminal point 22 (i.e. bearing pulses) are fed to the pulse amplifiers associated with aerials 1 ... 4 by means of a distributer-controlled gating system, comprised of a four-phase pulse generator 32 and gating devices 33 ... 36, in such fashion that consecutive pulses energize consecutive aerials in regular progression around the array to set up a bearing signal. The reference pulses from terminal point 20 are fed by means of a second distributer - controlled gating system, comprised of the generator 32 and gating devices 38 ... 41, to the central aerial 5 via delay devices 42 ... 45, which introduce delays such that the envelope of the time-modulation of the reference pulses simulates exactly the timemodulation envelope of the bearing pulses so that by phasecomparison between these two envelopes (e.g. at a mobile receiver) the azimuth bearing of the mobile receiver relative to the beacon station can be determined. A suitable receiver (e.g. aircraft mounted) for use with the present navigation system, comprises a radio receiver 51, Fig. 4, the output from which is fed to a multiplex pulse receiver 53 which supplies at terminals 54 ... 58 the signals corresponding respectively to the effective modulations of the pulses at terminals 18 ... 22 delivered by the transmitter 16, Fig. 1. The outputs at terminals 54 and 57, which correspond respectively to the call sign and traffic signal modulations, are fed to telephone receivers 59, 60 respectively, the outputs from 56 and 58, corresponding respectively to the reference signal modulation and the modulation of the equi-spaced pulses which arise from the distribution in space of the array-aerials, are fed to a phase comparison indicator 61 (e.g. a cathode. ray tube or phase-meter),'the reading of which gives an indication of azimuth bearing, and the output from 55, corresponding to the ranging tone, is fed to another phase-comparison device 63 in which it is phase compared with a wave of like frequency derived from a low-frequency source 64 which modulates a radio transmitter 65 to supply at the beacon station, Fig. 1, the ranging tone used to modulate the pulses at terminal point 19, Fig. 1, this phase comparison indicating the distance of the mobile receiver from the beacon station. Details of the'distributer and gating systems (see Group XL (b)] of Fig. 1 are described with reference to Fig. 3 (not shown). Specifications 594,530 and 635,472 are referred to.