GB768109A - Omnidirectional radio range system - Google Patents

Abstract

768,109. Radio navigation. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). Nov. 3, 1954, No. 31764/54. Class 40(7) Relates to a phase-comparison ' radio-navigation system of the type in which the directional radiation pattern of a beacon transmitter (carrier frequency F), is rotated at a frequency f1 to produce at a mobile receiver a signal of fundamental frequency f1 whose phase rela-. tive to a reference signal of fundamental frequency f1 is dependent on the bearing of the receiver from the beacon, the reference signal being transmitted omnidirectionally from the beacon' by frequency modulating a subcarrier which is amplitude modulated on to a carrier of frequency F. According to the present invention, the bearing sensitivity is increasably shaping the beacon directional modulation pattern, Fig. 4, such that the waveform, Fig. 5, of the bearing-dependent signal at the receiver comprises the fundamental f1 and the third and fifth harmonies f3 and f5 of rotation frequency, corresponding. reference signals of frequency f1, f3 and f5 being modulated on to subcarriers having frequencies Fl, F3 and F5 respectively. The beacon, Fig. 2, comprises three horizontal loop aerials 18, 19, 20 spaced apart 11#/24. The two outer aerials 19, 20 are rotated about the fixed central aerial 18 at a speed of f1/=90 c/s by a motor 1b and'are energized in phase opposition from an R.F. oscillator 11 (frequency F=1,000 Mc/s), at 25 per cent of the energization level of the central aerial 18. Reference signals f1, f3 and f5 from generators 5; 6, and 7 synchronized with motor 16 are applied at 8, 9 and 10 to frequency modulate corresponding subcarriers F1, F3 and F5 which are applied together with an output from R.F. oscillator 11 to modulator 12 whose output is applied via bridge 21 to the central aerial 18. At the mobile receiver, Fig. 3, the bearing signal output, Fig. 5, from the detector 26 is applied through an amplifier 27 to a phase discriminator 28 and the subcarriers F1, F3 and F5 from detector 26 are demodulated at 29, 30 and 31 to give reference signals f1, f3 and f5 which are applied to the discriminator 28 through geared phase shifters 38, 39 and 40 controlled by a dial 46 which indicates the required bearing when it is adjusted to give a zero output from discriminator 28 as indicated on the centre-zero meter 55. The output from discriminator 28 varies with the setting of dial 46 as illustrated in Fig. 6 which shows that two null positions are obtainable, if there is a 180 degree ambiguity, but that the sensitivity is a maximum in the region of the nulls.