Patent GB-1480490-A (GB)
Title: Transmission of radio navigation phase corrections
IPC: G01S5/10
Filed: 1974-07-03
Abstract: 1480490 Radio navigation SOC D'ETUDES RECHERCHES ET CONSTRUCTIONS ELECTRONIQUES 3 July 1974 [3 July 1973] 29518/74 Heading H4D A method of transmitting phase correction information to mobile phase-reception radionavigation receivers, particularly in a sequential radionavigation system of the OMEGA type, comprises receiving (120) at a fixed radiobeacon station Fig. 1, wave portions sequentially transmitted from the fixed stations of the navigation system to determine actual phase information in a multiplex sequence # M  (M=a, b, c, d) corresponding to the sequence of transmission a, b, c, d of the sequential radionavigation system; deriving (122) a phase correction signal (# M -# M <SP>1</SP>) M=a, b, c, d linearly related to the difference between the actual phase information # M  received from each fixed station and the theoretical phase # M <SP>1</SP> which should be received from each fixed station, a given phase correction signal being produced simultaneously with the phase information which is to be corrected; transmitting (112) from said radio-beacon station a signal amplitude modulated (112) in standard manner for local direction finding and, phase or frequency modulated (125) in accordance with the multiplexed sequence of phase correction signals; receiving (420) at a mobile receiver Fig. 4 said wave portions to determine therefrom phase information related to the position of the mobile receiver and receiving (140) also from the fixed radio-beacon station the signal modulated in amplitude for local direction finding and in phase of frequency for phase corrections of the received phase information, whereby filtering (412) and demodulating (411) said signal recovers the multiplexed phase correction signal ## M , the phase corrections being applied (421) to the determined phase information from the fixed stations so that each phase information is modified by the phase correction associated with it. Said method of transmitting phase correction signals is a development of the method described in Specifications 1,371,952 wherein a radio beacon (110, 111, 112, 113) of the kind transmitting ON-OFF coded CW to enable R.D.F. at the mobile receiver has the multiplexed sequence of phase correction signals, additionally phase or frequency modulated on to its carrier. A complete system may comprise, Fig. 2, the modified radio beacon of Fig. 1 acting as a master station I, and modified radio beacons III, V acting as slave stations, the master station transmitting an unmodulated reference tone of 20 Hz which is received by the slave stations and used for synchronizing means. Unmodified radio beacons II, III, VI may be present. The master station includes a sequence clock whereby control signals are transmitted to the slave stations and the stations' transmissions to the mobile receiver produced sequentially. A slave station, Fig. 3, has the theoretical phases # M <SP>1</SP> stored in phase shifters 3221 to which the received Q, # M  signals are fed, with the correct phase shifter being used by the sequenced control of switches at the outputs thereof. In the receiver of Fig. 4, amplitude threshold detector 415 disables Q demultiplexer 423 when the error signals are below a reliability threshold. In an alternative mobile receiver Fig. 6 (not shown) the error signals ## M  are demultiplexed into parallel analogue channels for correction with the received analogue # signals, the corrected # signals then being demultiplexed. Alternatively, Fig. 7 (not shown) the Q signals may be demultiplexed and the individual portions corrected by the corresponding error signals.