Patent GB-1333804-A (GB)
Title: Radio-navigation station
IPC: H04B7/08
Filed: 1971-07-08
Abstract: 1333804 Radio direction-finders and radio navigation THOMSON-CSF 8 July 1971 [17 July 1970 (2) 18 May 1971 (2)] 32234/71 Heading H4D In a radio direction-finder or radio beacon, of the basic kind utilizing a rotating cardioid pattern, a plurality n of identical aerials each having a rotating cardioid pattern are utilized and a receiving device (in the case of a directionfinder), or a transmitting device (in the case of a beacon), is successively connected to each of the aerials for a predetermined duration.  Direction-finders, Fig. 1.-Each aerial, e.g. 1, comprises a dipole 11 and a ring of dipole reflectors successively rendered operative. 1f # is the duration for which a reflector is rendered operative, clock pulses from a generator 10 at a repetition frequency f = (1/#) actuate a generator 7 to give a series of pulses S i  (i = 1, 2 ... N) where i is the position number of a reflecting dipole in each aerial and the pulses in each series have a duration # = T/N, the pulses of the series S i  being shifted by # relative to those in series S; - 1. Pulses J on line 42 are of repetition frequency F, the frequency of rotation of the cardioid patterns. In the course of a cycle of duration nT and taking the jth (j = 1, ... n) time interval of duration T, device 9 directs the N series S i  respectively to the corresponding reflectors of the jth aerial at the same time as it connects the centre dipole thereof to receiving device 8, synchronization of a phase signal with aerial pattern rotation being ensured by pulses J applied also to line 43. During the complete cycle of duration nT, the phases, relative to the reference phase, P + #P j  ensure where #P j  represents the error (due to reflected rays from the surroundings) corresponding to the jth aerial; averaging by low-frequency filtering in the receiver and by the bearing indicator yields a decreased final error, Figs. 2 and 3 (neither shown). Beacons, Fig. 4.-A phase beacon is based on a single-aerial rotating cardioid-pattern comprising an omnidirectional element fed by a first H.F. signal amplitude-modulated by a subcarrier which is itself frequency-modulated by the phase reference signal frequency F (about 30 Hz) and two crossed dipoles respectively fed with two other H.F. signals, of the same frequency #/2# and the same H.F. phase as the first H.F. signal, and of the respective forms (sin 2# Ft sin # t) and (cos 2# Ft sin # t). In the embodiment n = six such aerials 101 ... 106 are employed, the above three signals being provided by generators 108, 109, 110. The n aerials may be fed (i) successively, each for a duration T = 1/F, or (ii) successively, but each for a duration # = T/p(p>1), the number p being such that the fundamental switching aerial-switching frequency and its harmonics lie outside the low-frequency band in the corresponding receiver and also outside any lowfrequency bands used in auxiliary modulation of the H.F. signals (e.g. for identification and telephony). Other aerial dispositions mentioned are a diamond shape and, where the offending obstacle is known, a linear arrangement normal to the direction of the obstacle.