Patent GB-815138-A (GB)
Title: Improvements relating to pulse receivers
IPC: G01S1/20
Filed: 1957-04-04
Abstract: 815,138. Radio navigation. SPERRY RAND CORPORATION. April 4, 1957 [April 6, 1956], No..11086/57. Class 40 (7). In a pulse hyperbolic radio navigation system comprising two spaced stations A and B transmitting wave pulses of the same pulse recurrence frequency f in a predetermined time relationship, the carriers of the respective pulses being of the same frequency F and in a predetermined phase relationship, a coarse unambiguous indication of the time interval between the receipt of the A and B pulses at a mobile receiver is provided by determining the time difference between the envelopes of the detected A and B pulses and a fine but ambiguous indication of said time interval is provided by determining the phase difference between the carrier components of the received A and B wave pulses. The invention is illustrated as applied to a system in which the pulse recurrence frequency f is related to the carrier frequency F and in this case the time difference and phase difference determinations are controlled by a single master oscillator 20, Fig. 1, of frequency F. As shown, the envelope time difference is determined by applying an output from the master oscillator 20 through a first phase shifter 22 to a divider chain 26 giving a train of sampling pulses N, Fig. 3, which are automatically maintained coincident with the cross-over points of differentiated detected A pulses, Fig. 3, M, by a first servo loop 46, 52, 54, 56, 58, 23 controlling the phase shifter 22, further outputs from the divider chain 26 being applied to a variable B delay circuit 32 giving a train of sampling pulses O, Fig. 3, which are automatically maintained coincident with the cross-over points of the differentiated detected B pulses, Fig. 3B, by a second servo loop 60, 63, 65, 66, 68, 31 controlling the B delay circuit 32, the desired coarse indication being given by the setting of the delay circuit 32 as indicated by a counter 34. The carrier phase difference is obtained by applying a second output from the master oscillator 20 through a second phase shifter 69 to a phase detector 70 together with the received wave pulses to give an error signal which is applied through a gate 72 controlled by the sampling pulses N to a third servomotor 82<SP>1</SP> which controls the phase shifter 69 so that its output is in phase quadrature with the carrier of the A pulses, a further output from the phase shifter 69 being applied through a third phase shifter 82 which is automatically controlled by a fourth servo loop 84, 86, 90, 88, 92, 96, 94 so that its output is in phase quadrature with the carrier of the B pulses, the desired fine indication being given by the setting of the phase shifter 82 as indicated by a dial 98. Each of the servomotors 23, 31, 82<SP>1</SP>, 94 is of the two-phase type, the D.C. pulse error output from the corresponding gate 46, 60, 72, 86 being connected to a phase-dependent A.C. control voltage by means of an amplifier, low-pass filter, modulator and amplifier. The sampling pulses N, Fig. 3, are produced by a generator 50 triggered by pulses F, Fig. 4, derived in a fixed A delay circuit 30 from a square wave E of recurrence frequency f from a generator 28 triggered by pulses D of recurrence frequency 2f from the divider chain 26 which may comprise ganged phase-shifters as in Specification 654,979; the sampling pulses O are produced by a generator 64 triggered by pulses G from the variable B delay circuit 32. The gates 46 and 60 in the first and second servo loops may be replaced by a single sequentially-operated gate and the gates 72 and 86 in the third and fourth servo loops may be similarly replaced by a single loop as described in Specification 748,539; the third and fourth servo loops may be as described in Specification 773,670. When f and F are unrelated (see above) the first and third servos 23 and 82<SP>1</SP> are used to control the frequencies of the two master oscillators to bring their outputs into a predetermined phase relationship with the pulse recurrence and carrier frequencies respectively of the A wave pulses. The system is set up manually with the switches 25 and 35 in position M (manual) and the ganged switches 38 in position S (slow). The detected pulses, Fig. 3B, are applied to the Y plates of a C.R.T. 18 together with a waveform I, Fig. 4, formed by combining a trace separation waveform (inverted E waveform) with A and B pedestals, Fig. 4H, initiated respectively by F and G pulses, a slow timebase K of recurrence frequency 2f being applied to the X plates of the C.R.T. The displayed A and B pulses are first set on the corresponding pedestals, Fig. 2 (not shown), by controlling the phase shifter 22 and delay circuit 32 by means of sleeving controls 24 and 33. Switch 38 is then moved to position F (fast) thereby removing the waveform I and selecting a fast timebase L triggered by pulses J derived from the A and B pedestals, the leading edges of the superimposed displayed A and B pulses being aligned by further adjustment of delay circuit 32. U.S.A. Specification 2,651,033 also is referred to. Reference has been directed by the Comptroller to Specification 773,670.