Patent GB-1121096-A (GB)
Title: Radio navigation system
Inventor: EARP CHARLES WILLIAM
IPC: G01S1/22
Filed: 1965-10-01
Abstract: 1,121,096. Radio navigation system. STANDARD TELEPHONES & CABLES Ltd. 1 Oct., 1965, No. 41735/65. Heading H4D. The Specification describes a radio navigation system wherein an item of navigational information of the position of a mobile station with respect to a fixed station, e.g. its azimuth, elevation (glide slope for an aircraft) or range, is determined at the mobile station as the frequency deviation of a frequency modulated beat signal, produced from the beating of two signals received from respective spaced antennµ at the ground station, said signals being in the superhigh frequency range and having very nearly the same frequency, and being synchronously frequency modulated with the same signal. The antennµ system at a ground station adjacent an aircraft runway 76 and touchdown line 77 is shown in Fig. 7. The five antennµ radiate on mean frequencies, and relative amplitudes and provide navigational information at a co-operating aircraft as shown in the following table:- In addition the radiations from antennµ 74 and 75 are used to provide a V.O.R. 360 degrees, azimuth indication. Each radiated signal is frequency modulated in synchronism at 30 c/s. with a deviation ofŒ 80 Mc/s. Thus, if the mean frequency of the reference signal from antenna 71 is F, and that from antenna 72 is F+f 1 , then the beat frequency between the two signals at the aircraft having an azimuth angle of # with respect to the runway has a frequency deviation proportional to where Wm is the modulating frequency and d is the distance between the antennµ. Thus, said deviation gives an indication of the azimuth 0. The indication of the glide slope angle is derived from the beat between the signals from antennµ 71 and 73 in a similar manner. The frequency deviation of the beat between the signals from antennµ 71 and 74 varies with distance from line 77 as shown by curve 91, Fig. 9, and that of the beat between the signals from antennµ 71 and 75, as shown by curve 92. This, by applying deviation signals according to said curves to respective mutually perpendicular deflection coils of a ratiometer, the moving coil thereof and attached pointer will align to give a distance indication on a logarithmic range scale such as shown in Fig. 11. The transmitter at the ground station is shown in Fig. 8, wherein the 100 Mc/s. output of oscillator 22 is frequency modulated at 30 c/s. at 23 with a deviation of Œ2 Mc/s. The output of the modulator 23 is fed to mechanical modulators 82/85 which feed in quadrature side-band signals to respective sum and difference bridges 86, 871/873, such that bridge 86 gives output frequencies of 99.999975 Œ2 Mc/s. at 30 c/s. and 100À000025 Œ2 Mc/s. at 30 c/s. and bridges 871/873 give respective output frequencies of 100À0001 Œ 2 Mc/s. at 30 c/s., 100À00125 Œ2 Mc/s. at 30 c/s., and 100À00225 Œ2 Mc/s. at 30 c/s. These bridge outputs are applied to X 40 frequency multipliers 271/275, to give the signals for radiation by antennµ 71, 73, 75, 72 and 74 respectively. The aircraft receiver is shown in Fig. 10, wherein, due to its greater amplitude, the frequency modulation of the reference signal is produced by frequency discriminator 1021 and filter 1055, and an amplitude detector causes the signals from antennµ 72, 73, 74 and 75 to each beat with the reference signal for antenna 71 to produce the respective frequency modulated beat signals having average frequencies of 51 kc./s., 2 kc./s., 91 kc./s. and 5 kc./s. The frequency modulation of each beat signal is extracted by frequency discriminators 1041/ 1044 and filters 1051/1054. The amplitude of the output of filter 1052 determines the azimuth of the aircraft, and the sign of this azimuth is determined by the phase of the output relative to the reference 30 c/s. output of filter 1055. The outputs of filters 1052 and 1055 are thus fed in quadrature (90 degrees phase shifter 1067) to a phase discriminator 1062, and the output thereof is fed to an azimuth indicator 1072. The output of filter 1051 is fed directly to an amplitude sensitive slope angle indicator 1071. The outputs of filters 1053 and 1054, having amplitudes respectively given by curves 91 and 92 are fed to the crossed coils 1078, 1047 of ratiometer distance indicator 1073. The moving coil 1076, supporting the indicator pointer is energized by the reference output of filter 1055. The amplitudes of the outputs of filters 1053 and 1054 are respectively proportional to sin 0 and cos #. The output of filter 1053 is thus phase shifted at 1065 by 90 degrees and added in circuit 1066 with the output of filter 1054 to give a 30 c/s. signal having a phase relative to that of the reference signal equal to #. A phase discriminator 1075, receiving the outputs of circuit 1066 and filter 1055 thus gives the azimuth angle 0.