Patent GB-598701-A (GB)
Title: Improvements in or relating to the measurement of time intervals
IPC: G04F13/02
Filed: 1943-03-30
Abstract: 598,701. Radiolocation ; valve circuits. COCKCROFT, J. D., POLLARD, P. E., NEWSAM, B., BRITISH THOMSONHOUSTON CO., Ltd., and LUCAS, G, S. C. March 30, 1943, No. 20786/46. Divided out of 598,649. [Class 40 (v)] [Also in Group XXXVI] The subject matter is the same as that disclosed in Specification 598,649, which describes a radiolocation system in which range is determined by measuring the time interval between transmitted and reflected pulses, the echo signals being displayed on a slow-time base for coarse measurement and also, for accurate measurement, on a fast time-base which corresponds to one half-cycle of a standard frequency oscillation of adjustable phase ; the selection of the appropriate halfcycle being performed with the aid of a coarse range indicator on the slow time-base. The claims relate to the apparatus for the measurement of the short interval. Figs. 2 and 2A indicate the time-base and. control circuits for the range measuring cathoderay tubes of the radiolocation system of Fig. 1 (not shown). The one microsecond locking pulse from the transmitter, applied at terminal 29 is lengthened by diode 118 and circuit 119, 120 to a pulse of 240 microseconds which is amplified by valve 121 and fed to trigger the biassed multi-vibrator comprising valves 124, 125. Valve 125 is normally conducting to discharge condenser 126 but when the circuit is triggered valve 125 is cut-off and condenser 126 charges up through resistances 129, 130, 131 and the pentode 128. A linear sweep voltage is produced by allowing the rising voltage to cut-off the diode 132 and influence the grid voltage of the pentode 128. Sweep voltages from the cathode of valve 128 and the anode of phase-reversing valve 133 are applied in push-pull via leads 141, 142 to the horizontal-deflecting plates of the coarse range tube 26 across a mean zero potential provided by the earthed point E between resistances 143, 144. The time-base for the fine range tube 27 is sinusoidal and is produced by a lightly damped train of waves at 82 kc/s, generated in the circuit comprising inductance 173 and associated elements when valve 169 is cut-off by the fall of anode voltage of valve 124 on the triggering of the multivibrator. Quadrature voltages from the branches 174, 175 and 176, 177 are fed to phase-splitting valves 180, 181 and voltages phased respectively at angles of 0‹, 90‹, 180‹ and 270‹ are fed to the terminals of the phasepotentiometer 34 which comprises a circular potentiometer with padding resistances to ensure a uniform phase distribution. The output voltage from the wiper arm 186 which is thus capable of continuous variation in phase, is fed via the paraphase amplifier 187, 188 to the X plates of the fine range tube 27 which is normally biassed off. The blackout on the tube 27 is removed for a period of 6 microseconds, which corresponds to a range interval of 1000 yards and one half cycle of the fine range time-base wave, at a time determined by the adjustment of a coarse range potentiometer 32, a pulse being simultaneously fed to the coarse range tube 26 to brighten the trace and indicate the range interval visible on the tube 27. The H.T. supply fed to terminals 127, 148 is floating about the earth point E and to ensure that the initial value of the sweep voltage on the X plates of tube 26 bears a constant relation to the voltage across potentiometer 32, a " master " potentiometer 149, 150 is provided, the tapping 151 being connected to the grid of valve 152, the cathode of which is coupled through the normally conducting diode 132 to the grid of the charging valve 128. This link ensures that the initial sweep voltage and the voltage across potentiometer 32 are both fixed at a definite fraction of the supply voltage. Potentiometers 130, 153 enable adjustments to be made. Valves 157, 155 have the voltage from the potentiometer 32 and the sweep voltage respectively applied to their grids and a common cathode load provided by valve 156 maintains their grids negative with respect to their cathodes so that no grid current flows. When the sweep voltage exceeds the potentiometer voltage an impulse shock-excites the tuned circuit 159, 160 and a six microsecond pulse is produced by valve 161. These pulses are fed via valve 163 to brighten the trace on tube 26 and render visible the selected half-cycle of trace on tube 27. The flyback of the time-base on the coarse range tube 26 is eliminated by a voltage fed to its control grid from the screen circuit of the sine wave generator 169. The coarse range potentiometer 32 and phase potentiometer 34 are ganged, and when the control is adjusted so that the brightened portion of the trace on tube 26 overlaps a particular signal (applied to the Y-plates of the tubes) the signal also appears on the trace produced on tube 27 by the selected half-cycle of the sinusoidal time-base. If the control is then adjusted so that the selected signal is centred on the screen of the fine-range tube 27, the particular half-cycle of sweep voltage is passing through its zero value and the total phase shift which has been introduced by potentiometer 34 (complete rotations being effectively added up by the coarse potentiometer 32) is equal to the phase angle of the sinusoidal sweep voltage at the instant when the echo signal is received and the movement of the control handle may be calibrated directly in terms of time interval or range. Specification 582,325 also is referred to.