Patent GB-841582-A (GB)
Title: Improvements in or relating to electrical phase discriminators and algebraic multipliers
Inventor: EARP CHARLES WILLIAM
IPC: G06G7/161
Filed: 1957-03-20
Abstract: 841,582. Radio direction finding; phase discriminators. STANDARD TELEPHONES & CABLES Ltd. March 20, 1957, No. 9095/57. Classes 40(5) and 40(7). [Also in Group XXXVI] An electric circuit for algebraically multiplying two quantities respectively represented by the instantaneous phase difference between two waves and by the instantaneous amplitude of a multiplier wave of substantially lower frequency comprises means jointly responsive to the first two waves producing two interlaced squarewave pulse trains of period T and respective pulse durations T/2 (1 + #/#) and T/2 (1 - #/#) where # is the instantaneous phase difference, the voltage amplitudes of the trains being balanced about zero; means for clamping the amplitudes of the pulse trains to the instantaneous amplitude of the multiplier wave when such amplitude has a particular sign; and integrating means responsive to whichever clamped train has an instantaneous potential of such particular sign to derive a voltage waveform corresponding in amplitude to the product. When the multiplier wave amplitude is held constant the circuit operates as a phase discriminator whose output amplitude represents the phase difference between the first two waves. Input H F waves E, E < # differing in phase by # radians representing a first parameter are applied at 1, 3 (Fig. 1) to a pulse generator 4 (Fig. 3) wherein the respective waves are squared and differentiated in converters 29, 30 to two interlaced trains of sharp pulses of repetition period T = 1/f  where f is the input frequency; the leading edges of the trains differing in time by a half period (due to a transposition network 2 inserted in series with input 3) plus T #/# due to the phase difference #. A flip flop circuit 31 is triggered by the respective pulse trains at the grids of its alternate electron tubes 32, 33 from one to the other stable condition and back so that the tube anodes develop trains of rectangular pulses (Figs. 2A, 2B not shown) of repetition period T and duration respectively T (1 + #/#)/2 and T (1 - #/#)/2 which are connected over lines 5, 6, resistors 15, 18, and similarly poled rectifiers 16, 19 to opposite ends of an earth centre tapped secondary of transformer 10 energized from a low frequency source 9 whose amplitude represents a second parameter. The voltages at resistance/rectifier junctions 17, 20 due to the pulse trains are clamped so that they cannot move more positively than the output voltages at the respective ends of transformer 10, and the junctions are connected over simularly poled rectifiers 22, 23 so that the more positive junction voltage is applied to an integrating R-C network 24, 25, and a bias voltage from D.C. source 26 is applied to the junction of rectifiers 22, 23. (Figs. 5A-F not shown). The integrated voltage at terminal 25 is alternating at the frequency of energization of transformer 10 and of amplitude proportionate to the product of the two input parameters represented by angle #, and the voltage amplitude of source 9 over transformer 10 which may be replaced by unidirectional voltage sources of opposite polarities each returned to earth. An attenuator 90 and transposition network 91 may be connected between inputs 1, 3 whereby converters 29, 30 are maintained in operation on failure of either input to hold the discriminator output stabilized at a value corresponding to # = O. Buffer amplifiers may be inserted between the pulse train inputs and the clamping rectifiers and between the latter and the integrating circuit (Fig. 4 not shown). In an application (Fig. 6) to a radio direction finding system, an array 61 of nine antennae is uniformly spaced round a circle of radius R and each is commutatively coupled in regular succession at frequency F by switch 62 controlled by unit 64 to receiver-mixer 63 for one millisecond; the whole cycle being repeated at frequency F/9.   Mixer 63 energized by beat oscillator 66 generates an intermediate frequency signal selected by filter 67 for mixer 68, while reference antenna 69 is similarly coupled to a receiver mixer 70 energized from oscillator 66 to generate intermediate frequency signals for mixer 72 energized from stabilized oscillator 73 at frequency Fo to generate lower and upper sidebands of which the latter are selected by filter 74 and applied to mixer 68 to yield inter alia a difference frequency signal of frequency F o  and phase corresponding to the instantaneous phase difference between the inputs to mixers 63 and 70, and is thus phase modulated at the commutation frequency F and phase determined by the angle # with a reference direction made by the direction of the received signal. The emergent signal selected by filter 75 is given by E # # = E sin [2# Fo t + α sin (2# t + #)] where # = α sin 2# (Ft + #) α = 2#R/# - the maximum phase modulation due to scanning. # = the operating wavelength and is applied to a pair of phase discriminators 76, 77 of the kind described above together with the output of oscillator 73; the low frequency sources 78, 79 being energized in quadrature from unit 64 at a frequency isochronous with the scanning. The discriminator outputs are applied to the X, Y plates of cathode ray oscillograph 80, and it is shown that they are respectively given by # cos 2# Ft = #/2 [sin # + sin (4# Ft + #)] and # sin 2# Ft = α/2 [cos # - cos (4# Ft + 0)] so that the display (Fig. 7) is a circle of luminous spots 82 intersecting the origin 83 and corresponding to the respective antennae of the array intersected by a diameter indicating the direction of the received signal. Specifications 594,530 and 758,139 are referred to.