Patent GB-1141180-A (GB)
Title: Improvements in or relating to phase comparison radio navigation systems
Inventor: YOUNG REX ALAN
IPC: G01S1/30
Filed: 1966-12-07
Abstract: 1,141,180. Radio navigation. DECCA Ltd. 13 Oct., 1967 [7 Dec., 1966], No. 54734/66. Heading H4D. [Also in Division H2] In a radio navigation system comprising a mobile receiver 17, Fig. 1, determining its position by measuring the phase relationship between radio-frequency signals, transmitted by respective master transmitting station 10 and three spaced slave stations 12, 13, 14 each normally radiating only one characteristic frequency at a time but also having identification means to radiate simultaneously signals at frequencies of 5F, 6F, 8F, 9F and 8À2F where F is a common fundamental frequency; all the radiated signals from any one transmitting station have a substantially fixed multiphase relation to a locally generated pulse at a frequency of 0À2F, the means for generating the 0À2F pulses at each slave station, Fig. 8, including an oscillator 103 adapted (divider 106) to produce 6F pulses, a thirty-to-one frequency divider 108 dividing down the 6F pulses and having means to phase step the resulting 0À2F pulses along in time steps of one or more whole numbers of 6F cycles on command and one of the stations transmits timing and coded phase control command signals, derived at a control monitor station 18, receiving all the transmissions, as modulations of the 8À2F signal. A clock divider operates from each oscillator and comprises a pulse counter and coincident gating means to provide signals controlling a transmitted signal programme, whereby there is a normal period of transmission during which the master station radiates only a signal of 6F and each slave station radiates a respective one of the frequencies 5F, 8F and 9F, a master break period during which no station radiates a signal of 6F, and a series of lane identification periods, in which each station, in turn, radiates signals of frequencies 5F, 6F, 8F and 9F simultaneously, the other stations not then radiating on these frequencies. Each slave station has means 90, 111, 92 for receiving and amplifying the 6F signals radiated by the master station, means including a phase discriminator 101 for controlling the frequency of the oscillator 103 output, by determining the phase difference between a 6F signal derived from the oscillator and the received 6F signals whereby said difference is reduced to zero, a receiver 91 for receiving and amplifying said modulated 8À2F signals from said one station, means 93 for rectifying the 8À2F signals from said receiver to convert them into interrupted direct current signals for synchronizing via 98 and 99 said signal programme with said timing signals and for controlling the stepping of the 0À2F pulses via 96 and 97 with said phase control command signals. The control station includes a five-channel receiver for receiving each of the different radiated frequencies, a local oscillator controlled in frequency and phase by the received 6F signals, a frequency divider coupled to the oscillator to produce a reference IF signal, a phase indicator for each slave to indicate the phase difference at the least common multiple of the master and corresponding slave received signals during said normal period, a phase indicator to indicate the phase difference between the reference 1F signal and the 1F signal derived from four transmitted signals received from one station during each lane identification period, a signal generator producing a signal having components at each of the five transmitted frequencies with fixed multiple phase relationships, means for coupling said components into said five-channel receiver in place of the respective received signals to standardize the phase indicators, an 8À2F receiving channel to receive sequence timing information from the transmitting stations, and means responsive to the indicated phase differences for transmitting said phase control command signals to the transmitting stations whereby the coarse pattern of equiphase position lines is determined with reference to a frequency of 0À2F. Fig. 2 shows part of the master station which comprises three phase locked master oscillators, one 20 being in the active mode and the other two (not shown) being in stand-by. The output of the oscillator of 64X6F is divided down at 21 to a 0À2F frequency and a 6F frequency. The 6F frequency is used to control a local clock 22 synchronizing the various transmissions and the 0À2F frequency is converted into very short pulses of 0À2F p.r.f. which contain all harmonics of F. Harmonics 5F, 6F, 8F, 9F and 8À2F are extracted in phase locked relationship by tuned amplifiers 25. The output of each tuned amplifier is fed to one side of a phase discriminator 26. The other sides of the discriminator is fed by a second tuned amplifier 27 receiving a sample of the transmitted signal from aerial 50. The output amplifier 25 is fed to the transmitting amplifiers 36, 37 via an adjustable phase shifter 28 under the control of the output of the discriminator. The system thus adjusts until the phase difference of the inputs to the discriminator is zero. The signal is transmitted in its correct order by means of an opening signal from clock 22 applied to gate 32. The output of each transmitting amplifier is coupled to the aerial 50 by a series of primary coupling coils 60, 61, 62, 63, 64 and tuned secondaries 53, 54, 56 such that the aerial is neutralized for all transmitted frequencies and no cross interference occurs. A coil 66 detects the sample for feeding to amplifiers 27. Much of the described master station equipment is repeated in the control station and the transmission of the 8À2F signal is pulse code modulated by information received from the control stations.