Patent GB-1319634-A (GB)
Title: Navigation systems
IPC: G01S1/30
Filed: 1970-07-31
Abstract: 1319634 Radio navigation TELEDYNE Inc 31 July 1970 [1 Aug 1969] 37222/70 Heading H4D  In an OMEGA phase comparison navigation system adapted to overcome skywave interference, a relay station 16, Fig. 1 is provided at a fixed known position in the vicinity of the mobile station 18, such that it may be assumed that the signals received at the relay station from the transmitting stations A, B, and C undergo the same skywave phase shifts # A , # B  # C  as do those received by the mobile station. The use of the 10À2 KH 3  transmission only is described. At the relay station (Fig. 3, not shown) each received 10À2 KH 3  signals mixed with the output of a phase locked oscillator at 10À5 KH 3 , to give a 300 H 3  signal phase locked to the received 10À2 KH 3  signal, which 300 H 3  signal is amplitude modulated on to a 1750 KH 3  carrier. At the mobile station the 10À2 KH 3  signal from station A is received at receiver 24 with a phase shift # A18  + # A  and the modulated relay carrier is received at 22 with a phase shift #A.16+#A+# 16À18 , where # AÀ18 , # A16  and # 16À18  are the propagation phase shifts between stations A and the mobile stations 18, between stations A and the relay station and between the relay station and the mobile station, respectively. The receivers 22 and 24 produce signals of equal frequency from the received signals, phase locked therewith, and feed these via synchronous commutators 26, 28 operating in synchronism with the transmission - to a phase comparator 30. The phase difference presented at 30 and indicated thereby is: # A.16  - # A18 +# 16.18 , i.e. the skywave effect is cancelled out. Similarly phase comparators 32 and 34, respectively receiving the direct and relayed transmission from stations B and C indicate: # B.16  - # B.18 +# 16.18  and The comparators have shaft rotation outputs such that mechanised differentials 36 and 38 coupled to the shafts of comparators 30/32 and 32/34 respectively, give outputs at 40 and 42 indicative of the phase differences:  Since the relay has a known position the terms (# A16  - # B.16 ) and (# B.16  - # C16 ) one known and can be compensated for, thereby leaving the position line defining phase differences, In the arrangement of Fig. 2 (not shown), the differential resolves 44 and 46 are used as phase shifters to shift the phases of the A station signals received by receiver 24 and receiver 22 respectively under the control of phase comparator 32. Comparators 40 and 42 then determine the phase differences between the respective phase shifted signals and the signals from receivers 22 and 24 to give the same indicated final indications on 40 and 42 as given above. The phase comparators 30, 32, &c. may be replaced by balanced mixers feeding phase storage means (Fig. 5, not shown). The phase storage means may be updated by navigational aids e.g. inertial nagivation means and may comprise (Fig. 6, not shown) a phase detector detecting the phase difference between the balanced mixer output and that of a voltage controlled oscillator. The intermittent detector output is stored in an integrator, being fed as a continuous signal to control the oscillator. The output of the oscillator constitutes the output of the phase storage means.