Patent GB-1132283-A (GB)
Title: Radio navigation beacon and receiver
Inventor: EARP CHARLES WILLIAM
IPC: G01S1/22
Filed: 1966-01-28
Abstract: 1,132,283. Radio navigation. STANDARD TELEPHONES & CABLES Ltd. 28 Jan., 1966, No. 3897/66. Addition to 1,121,096. Heading H4D. Relates to a modification of the system of Specification 1,121,096 wherein the plurality of spaced antennµ are disposed respectively (a) at the vertices of an isosceles right-angle triangle; (b) at the vertices and centre of a square; and (c) at the vertices and base centre of a square based pyramid; the antenna (a) at the right angle or (b) and (c) at the square centre being of greater radiating power than the other antennµ. The receiver of Fig. 4 is designed to work with a beacon comprising four antennµ A, B, C and D arranged at the corners of a square, a fifth antenna Q at the centre of the square, and a sixth antenna E arranged vertically above antenna Q, the antennµ radiating signals at centre frequencies of F + 170 kc/s., F - 130 kc/s., F - 150 kc/s., F + 110 kc/s., F and F Œ 90 kc/s. respectively, all synchronously frequency modulated at F.M. = 15 c/s. with a frequency deviation of 80 Mc/s. The amplitude of the signal at frequency F is very much greater than the other signals. The received six signals are detected at 2 to produce frequency-modulated beat frequencies of 170 kc/s., 150 kc/s., 130 kc/s., 110 kc/s. and two signals at 90 kc/s. The two beats of 170 kc/s. and 150 kc/s. are selected by filter 43, and have frequency deviations representing AP-QP and QP-CP respectively, where P is the position of the receiver. These two beats are further beaten together in detector 46, to produce a sum beat at 320 kc/s. representing AP-CP and a difference beat of 20 kc/s. representing AP + CP - 2QP. In a similar manner a sum beat at 240 kc/s. representing DP-BP and a difference beat at 20 kc/s. representing 2QP-DP-BP are produced from the 130 kc/s. and 110 kc/s. beats. The two difference beats are beaten together in detector 50 to produce a difference frequency signal due to the difference in the frequency deviation of the two beats, representing (AP + CP - 2QP) - (2QP - DP - BP) = AP + BP + CP + DP- 4QP. This, except for close proximity to the beacon, is proportional to the reciprocal of the distance QP. The difference frequency signal is therefore converted to a pulse signal by limiter 51 and the pulses counted over a modulation cycle in counter 52, to give an indication of 1/OP. The frequency deviation of the beat signal at 320 kc/s. is determined by mixing the beat signal with a 320 kc/s. signal from oscillator 6. The resultant frequency deviation sign is converted to a pulse signal in limiter 14 and counted in counter 22, to produce an indication of Cos #, where # is the bearing of the receiver with respect to the line AC. The received signal at frequency F from Q is passed to a frequency discriminator 3 to produce the modulator frequency at 15 c/s. The beat signal at 320 kc/s. is also frequency modulated at 15 c/s. and produces a modulator frequency at 15 c/s. by means of frequency discriminator 11. After being phase shifted by 90 degrees, the phase of the first 15 c/s. modulation signal is compared with that of the second modulation signal in differential detector 19. They are either in phase or in antiphase. A corresponding signal is fed to the counter 22, indicating that # is positive or negative respectively. In. a similar manner the beat signal at 240 kc/s. produces an indication of Sin # and an indication of the sign of #. The elevation # of the receiver is provided by the two 90 c/s. beat signals which have equal and opposite frequency deviations proportional to Sin #. The two beats are therefore beaten in detector 53 and the pulse signal derived from the difference frequency output of the detector fed to a counter 55.