Patent GB-773670-A (GB)
Title: Improvements in or relating to phase-measuring and synchronising apparatus
Inventor: CRIST PHILIP WIDDECOMB
IPC: G01S1/24
Filed: 1953-01-14
Abstract: 773,670. Phase measurements. SPERRY CORPORATION. Jan. 14, 1953, No. 1162/53. Class 37. [Also in Group XL (c)] Apparatus for measuring the phase relationship between the carrier-frequency components of first and second modulated high-frequency signals comprises means for producing a first unmodulated signal alternating at the frequency of the carrier-frequency component of the modulated signals and having a predetermined phase relationship with the carrier frequency component of the modulated signals of the first train; means for producing a second unmodulated signal alternating at the frequency of the carrier-frequency component of the modulated signals having a predetermined phase relationship with the carrier-frequency component of the modulated signals of the second train; and means for measuring the phase relationship between the first and second unmodulated signals to produce a measure of the phase relationship between the carrier-frequency components of the first and second modulated signals. The apparatus may be used in a receiver for a " precision Loran " radio navigation system. In one such arrangement, Fig. 2, received signals are applied to a R.F. amplifier 11, from which an output to a detector 12 and a pulse time comparator and trigger pulse generator 13. An output from the R.F. amplifier 11 is also fed to a phase detector in each of the three servo loops. The first servo loop includes an oscillator 37 of high-frequency stability which may be tuned to the frequency of the master transmitting station. The output of the oscillator passes through a phase shifter 38 to the phase detector 39 of the first servo loop and also to the phase shifters of the second and third servo loops. Phase detector 39 compares the phase of the input from phase shifter 38 and of the pulses from the master transmitting station and passes an output to a sampling gate 42. The trigger pulse generator 13 generator trigger pulses at the instant when the received pulses attain a predetermined amplitude which is low compared to their peak amplitudes; these trigger pulses are delayed by a delay circuit 43 in each of the servo loops so that the sampling gates 42 are opened at a time at which the radio-frequency cycles of the pulses have attained appreciable magnitude but at a time prior to the occurrence of sky wave interference. Thus the output of the phase detector 39, after passing through a filter, an amplifier, and the sampling gate 42, is fed through a smoothing filter 44 to a servo amplifier 45 which operates a motor 46 which drives the phase shifter 38 so that the output of the phase shifter 38 is in phase with the radiofrequency component of the received pulses. The second and third servo loops are similar to the first, but the servo motors 46<SP>1</SP>, 46<SP>11</SP> also drive indicators 58, 58<SP>1</SP> which indicate the phase relationship between the pulses. In a modification, Fig. 7 (not shown), the sampling gate 42 and delay circuit 43 are omitted and trigger pulses from the unit 13 are used to open gates between the R.F. amplifier 11 and each of the three servo loops so that approximately one half of each received pulse is applied to the appropriate servo loop. In a further modification, Fig. 6, the servo amplifier, motor and phase shifter are replaced by a reactance tube circuit 60 which controls an oscillator 37 in each servo loop. The phases of the three oscillators are then compared in known manner. Specifications 509,139, [Group XL], and 609,298 are referred to.