Patent GB-1419965-A (GB)
Title: Radio method of determining the exact position of an object
IPC: G01S5/08
Filed: 1972-10-24
Abstract: 1419965 Radio navigation E A MOSYAKOV J V RTISCHEV E Z BERER V M LEUS V P LUKEEV E M RODIONOV V L LEVITSKY V S AKOPYAN J X MINDLIN E I BALASHOV I E KINKULKIN G P SHUMAKOVA E T FEDOTOV and V E LAZAREV 24 Oct 1972 49012/72 Heading H4D General.-This is a phase comparison path difference hyperbolic navigation system using one main station and two auxiliary stations. The general transmission format is shown in Fig. 1a wherein in a one second overall cycle the full transmission periods T1, T2, T3 and T4 are used all of 220 m.sec. duration and spaced by gaps of 30 m.secs., transmission intervals T1 and T3 being used by the main transmitter, interval T2 being used by the first auxiliary transmitter and interval T4 being used by the second auxiliary transmitter. An auxiliary transmission comprises (Fig. lb), within a cycle t of 1À2 m.sec., four pulses of duration ti= 150 Ásec. and of successive frequencies f1, f3, f4 and f2 the pulses being grouped into pairs as shown with gaps of 300 Ásec. separating the pairs. The transmission from the main station is similar except for the addition of a synchronizing pulse at a frequency f5 in the gap between the said pairs of pulses. Auxiliary transmitter, Fig. 2. Production of transmission format. Fig. 1b.-A reference oscillator 1 produces a 100 kHz reference signal which after passing through variable phase shifter 3, switch 17 and respective variable phase shifters 4, 5, 6 and 7 is applied in parallel to respective amplitude modulators 8, 9, 10 and 11. The modulators are fed with respective pulses from an auxiliary pulse shaping unit 27 the pulses on any one output being at 100 Hz shaped as indicated in Fig. 1b and relatively positioned with respect to the other outputs to give the pulse pairing and positioning of Fig. 1b. The collective outputs of the modulators similar to Fig. lb but at 100 kHz are fed to the bank of frequency changers 12, 13, 14, 15 fed with respective outputs from a frequency generator 26 at respective frequencies f1-100 kHz, f2-100 kHz, f3-100 kHz, f4-100 kHz. The outputs of the frequency changers are thus at the required frequenciesi f1,f2,f3 and f4 and when combined in amplifier 19 and transmitter 20 give Fig. 1b. Synchronization with master signals.-The auxiliary transmission has to be synchronized, both with respect to pulse envelope and carrier, with the corresponding transmission from the master station. The envelope synchronization is in two stages, coarse and fine. For the coarse stage the received f1, f3, f4, f2 transmissions of the master are passed to wide band filters 37, 38, 39 and 40 respectively tuned to f1, f2, f3 and f4, whereby the pulses are separated out and the separated pulses are returned to a common frequency of 100 kHz by means of frequency changers 41, 42, 43 and 44 fed with the aforesaid outputs of frequency generator 26. Switch 45 is now closed so that the pulses at 100 kHz derived from the master f1 transmissions are fed to early and late gates 53 and 54 receiving gating signals from a gating generator 74 whereby they are open for the first half and the second half respectively of a period t. The situation sought is that the pulse shall be half in the early gate and half in the late gate. When however the pulse is only within one of the gates, e.g. gate 53 and the other gate 54 passes only noise the output of a narrow band filter sharply tuned to a 100 kHz will be significantly higher than that of a similar narrow band filter 57 at the output of gate 54. The outputs of the narrow band filters are made sequential by means of sequentially enabled gates 59, 60 and combined in a summer 61 whereby the summer produces an amplitude modulated signal the amount of modulation being dependent on the difference of content of the signals passed by the early and late gates i.e. for the sought situation there would be no modulation. The modulation is therefore detected by amplitude detector 62 the output of which is used to control a variable phase shifter 70 which in turn, via switch 71, controls gate generator 74 such that the early and late gates bisect the pulse at their intersection. The output of detector 62 is used to control phase shifter 72 which, via a reference phase shifter 137, controls phase shifter 29 determining the timing of the four sets of modulating pulses at 800 Hz produced by generator 27. Reference phase shifter 137 contains fixed phase shifts representative of the known transit times from the master station to the auxiliary station. The phases of the outputs from generator 27 are thus adjusted such that the outputs from modulators 8, 9, 10 and 11 are all in the correct timing relationship with respect to the signals from the master. When this coarse control has been completed the wide early and late gates from generator 74 are replaced by two narrow gates having durations equal to half that of the pulses i.e. 75 m.sec. the method of the fine tuning being exactly the same as for the coarse. The phases of the carriers f1,f2,f3 and f4 have now to be adjusted to specific inter-relationships. For this purpose the carrier frequency f1 is phase matched with the carrier frequency f1 as received from the main station and the thus matched f1 signal is used as the reference for the phase matching of the other three carriers f2,f3 and f4. A received pulse frequency f1 is therefore converted to one at 100 kKz as previously described and passed to gate 37 to which is now applied a gating signal having a duration of 150 Ásec. i.e. equal to the pulse width. Due to the previous fine tuning this gating pulse should exactly coincide with the 100 kHz pulse. Such gating removes any sky wave interference. The narrow band filter 57 produces a continuous wave at 100 kHz which wave is applied to one input of a phase discriminator 24. The signal, derived from phase shifter 3 via key 17 and key 22 closed during the transmission time T3 of the main station, is applied to the other input of the discriminator. The output of the phase discriminator is used to adjust phase shifter 3 until the desired phase inter-relationship is achieved. It is now required to phase match the /1 signal as transmitted by the auxiliary station with that received from the main station taking into account the known propagation time phase shift between the main station and the auxiliary station. The f1 signal from the auxiliary station as transmitted is therefore converted to the 100 kHz signal as described above and passed to one input of the discriminator 24. The other output of the discriminator is fed with the output of phase shifter 3 via a further preset phase shifter- 23 containing said propagation phase shift and now shut switch 25. The output of the discriminator 24 controls phase shifter 4 until the desired phase matching is achieved. In the main station such phase matching is not needed and not provided. To provide for the correct phasing of the signals at f2, f3 and f4 a reference frequency shaping unit 76 receives the output of the 100 kHz generator 1 via phase shifters 3 and 75 and also the output of the generator 26 at frequency f1-100 kHz. The output of the shaping unit 76 passes via a gate 78 opened for the time that the main station is not transmitting to a reference pulse shaping unit 79 to produce a correctly shaped short pulse containing frequency f1, f2, f3 and f4 as harmonics of a common sub-frequency. The frequencies will be naturally in a fixed phase relationship. The four frequencies are separated out by filters 37, 38, 39 and 40 and converted to respective 100 kHz signals in frequency changes 41, 42, 43 and 44. The transmitted pulse frequency f1 also passes through filter 37 but at a different time. Gating stages 54 and 55 are respectively opened such that the transmitted pulse passes through gating stage 54 whilst the component signals at f1 pass through stage 55. After conversion to continuous signals via the narrow band filters 57 and 58 the phase discriminator 24 determines any phase differences between the transmitted pulse and the component pulse, the output of the discriminator being used to adjust phase shifter 75. The transmitted pulse at frequency f2 is then phase compared with the component pulse at frequency f2 in discriminator 24 in the same manner as described for the frequency f1 and the output of the discriminator 24 used to vary the phase shifter 5 the output of the narrow band filter 58 being passed to the phase discriminator via a reference phase shifter 64 wherein any desired phase relationship can be set. The relative phases of the f3 and the f4 transmitted pulses are then set up in a similar manner using preset phase shifters 65 and 66 and variable phase shifters 6 and 7. This completes the setting up of the auxiliary station, the transmitted pulses having the correct timing relationship, i.e. their envelopes, with respect to the transmissions from the main station and their carrier frequencies f1, f2, f3 and f4 having the correct phase relationships with each other i.e. as exhibited by corresponding harmonic frequencies of a narrow pulse as modified by the set phases in phase shifters 64, 65 and 66. Receiver.-At the receiver position display station Fig. 3 search for the master and the auxiliary f1 pulse transmission is carried out in two stages using wide, early and late range gates and narrow, early and late range gates in a manner similar to that already described for the ground stations. For the reception of the main station f1 pulse the pulse is received and passed through filter 88 changed to 100 kHz in mixer 92 and passed to early and late gates 100, 112. These are enabled for the first stage by wide, early and late range gates respectively, the gated pulse and/or noise converted to continuous signals by narrow band filters 102 and 113 and the continuous outputs alternately applied to a summer 107 by modulators 106, 114 to produce an output signal which has an amplitude v