Patent GB-795266-A (GB)
Title: Phase comparator applicable to direction determination of a target
IPC: G01S7/62
Filed: 1955-12-23
Abstract: 795,266. Phase difference measurement. BENDIX AVIATION CORPORATION. Dec. 23, 1955 [Jan. 3, 1955], No. 36912/55. Class 37. [Also in Groups XXXVIII and XL (c)] Apparatus for producing at two output terminals a potential difference indicating the phase difference between two input alternating voltages (which may represent e.g. the angular bearing of a vibratory wave reflecting target from a directional transducer) comprises a circuit deriving from the inputs a third voltage in phase quadrature with the mean phase of the inputs, a pair of cathode follower assemblies each having two cathode followers with interconnected anodes and cathodes and separate grids, and connections applying the third or quadrature voltage to one grid of each assembly and for applying to the remaining grids respective alternating voltages representing in phase the corresponding input voltages; the common cathodes of each assembly being connected respectively to the output terminals. In Fig. 1 a multi-unit directional underwater acoustic transducer 10 of known type is axially divided into independent halves 10b, 10c which are alternately excited from transmitting power source 19 and connected to receiving input terminals 15, 16 by contacts of relay 14 in response to timer 48. Voltages E1, E2 developed at terminals 15, 16 by the reception of echo sound waves from a target are separately amplified, respectively shifted in phase by - 45 degrees in networks 20a, 20b to E1a, E1a; and are also vectorially combined to voltage E3 which is phase shifted by + 45 degrees in network 20c to E3a; the three output voltages being then converted to square wave voltages E1b, E2b, E3b (Figs. 4 and 5) by limiters 21a, 21b, 21c. The squared voltages E1b, E2b are respectively capacitance coupled to the grids 25a, 26a of double triodes 25, 26 connected as cathode followers having an earth tapped balancing potentiometer 29a as their cathode load, and their remaining grids 25b, 26b are excited from the squared vectorially combined voltage E3b all in combination with a variable bias from battery 50 and a sawtooth waveform derived over isolating resistances 51 from generator 47 synchronized with timer 48. The resultant combined cathode voltages E6, E7 in the form of rectangular unidirectional voltage pulses of variable duration superimposed on the sawtooth are smoothed by resistancecapacitance circuits 29, 31, 30, 32 to sawtooth voltages E6a, E7a of variable slope which are amplified by valves 35, 40, 36, 41 and cathode coupled as voltages E6b, E7b to the horizontal deflection plates of cathode-ray oscilloscope 44 whose vertical deflection plates are excited by the sawtooth generator 47 and whose modulation electrode is energized from the voltage E3a at the output of phase shifter 20c over amplifier 52 and potentiometer 53. In operation, when a reflected target signal arrives along the centre line of transducer 10, voltages E1, E2 and E3 are in phase and voltage E3a is in quadrature with voltages E1a, E2a (Fig. 2, not shown). The combination rectangular waveforms E1b, E2b, E3b developed on the appropriate cathode follower grids cyclically increase from initial values at which the peaks are at cut off to final values at which the troughs are at cut off (Fig. 4) and the potentials of the combined cathodes of each valve 25, 26 respectively follow the greater positive grid potential so that the cathode voltages E6, E7 respectively remain at constant maximum values while either of voltages E1b, E3b or E2b, E3b are at peak, and fall to minimum only when both the appropriate components are at their trough values. By reason of the 90 degree phase shift between E3l and E1b, E2b the waveforms of E6, E7 are at peak for 270 degrees of each cycle and at trough for 90 degrees, and are thus identical, as are the respective smooth voltages E6a, E7a, so that the deflection voltages E6b, E7b are also equal in magnitude and angular slope and there is zero horizontal deflection of the trace on the C.R. screen, which remains vertical, indicating that the target is on the transducer centre line. Since the amplified voltage E3a derived from potentiometer 53 in response to the vectorial sum of the transducer voltages is displaced in time from the transmit/receive changeover and from the indication of the C.R. deflection sawtooth by an interval proportionate to the echo time and the target range, it is applied to the beam modulation electrode to brighten the trace 60 at a sweep position 60a dependent on the range. When the reflected target signal arrives off centre of the transducer (17, 18), the voltages E1, E2 correspondingly differ in phase. As before the voltages E1, E2 are phase retarded by 45 degrees and the vectorial sum E3 is advanced 45 degrees (Fig. 3, not shown) so that the corresponding rectangular voltages E1b, E2b, E3b are combined in the cathode followers to produce resultant rectangular cathode voltages E6, E7 (Fig. 5) wherein the durations of positive excursions in E6 exceed those in E7 and the durations of the negative excursions of E7 exceed those in E6 or vice versa in correspondence with the phase difference. Consequently the angular slopes of the smoothed voltage E6a and amplified deflection voltage E6b correspondingly exceeds the slopes of voltages E7a or E7b or vice versa in response to the phase difference, so that in conjunction with the vertical deflection sawtooth the oscillograph trace is deflected by voltage (E6b-E7b) which also has a sawtooth form, synchronous therewith, so that the trace 60 indicates the bearing of the target referred to the vertical axis of the oscillograph, and is brightened as before at 60a to indicate the target range on the required bearing.