Patent GB-805311-A (GB)
Title: Improvements in or relating to direction finding apparatus of the type using wave energy
IPC: G01S7/62
Filed: 1956-04-20
Abstract: 805,311. Phase difference measurement. BENDIX AVIATION CORPORATION. April 20, 1956 [May 2, 1955], No. 12163/56. Class 37. [Also in Groups XXXVIII and XL (c)] In a radiant energy directionfinder (see Groups XXXVIII and XL (c)), the phase difference between two signals E1 and E2 received respectively by two spaced transducers is indicated on a C.R.T. by the angular position of a radial trace produced by a sawtooth voltage Es. The signal E1 is applied to a 45 degree phase retardation circuit 55 giving an output E1a, Fig. 8a, and is also combined with the signal E2 to give a resultant signal E3 which is 45 degree phase advanced in a circuit 54 giving an output E3a. The signal E3a is amplitude limited at 58, giving a corresponding square-wave train of constant amplitude which is applied to a limiter circuit comprising valves 62, 64 which limit the positive and negative excursions in accordance with the instantaneous amplitude of the sweep voltage Es which is applied thereto from the control unit 36, Fig. 1 (not shown), via lead 49 and cathode follower 70. The output from the limiter 62, 64, thus comprises a sawtooth-modulated square wave E3b, Fig. 9, which is applied in push-pull (waveforms E3b and E3bi) to the grids of cathode followers 77, 76 and a corresponding waveform E1b derived from the E1a signal by a limiter 63, 65 is applied in phase to the grids of cathode followers 78, 79. Since the cathode followers 77 and 79 have a common cathode impedance the output therefrom E6 follows the positive portion of that one of the two applied waveforms E3b or E1b which is of greater amplitude; a corresponding waveform E7 is derived in cathode followers 76, 78 from the signals E3bi and E1b. The waveforms E6 and E7 have the same sawtooth envelope but different mark space ratios which are dependent on the relative phase of the input signals E1, E2. The signals E6 and E7 are then integrated respectively in R.C. circuits 97, 99 and 96, 98 to give sawtooth waves E6a and E7a which differ in slope in accordance with the sense and magnitude of the phase displacement between E1 and E2 and this difference is so accentuated by amplification in amplifiers 91, 90 having a common cathode feedback resistor 80 that the resultant outputs E6b and E7b may slope in opposite directions but the magnitude of the slope of the difference (E6b-E7b), Fig. 9, is linearly proportional to the phase displacement between E1 and E2 and the sense of said slope depends on the sense of said displacement. The outputs E6b and E7b are applied over leads 17R, 17L to a switched resolver, Figs. 1 and 5 (not shown), where they are combined with the sweep voltage Es and applied to the X and Y deflection members of the C.R.T. In the simplest condition of the resolver the sweep voltage Es is applied to the Y deflection coil and the outputs E6b and E7b are applied to the opposite ends of the X deflection coil to produce a resultant X deflection proportional to (E7b- E6b). The angular deviation of the resultant trace from the vertical position then indicates in sense and magnitude the phase difference between E1 and E2.