Patent GB-592619-A (GB)
Title: Improvements in time interval measuring systems particularly for use with object locating devices
IPC: G01S7/282
Filed: 1944-07-19
Abstract: 592,619. Radiolocation; thermionic valve circuits. WESTERN ELECTRIC CO., Inc. July 19, 1944, No. 13867. Convention date, Oct. 19, 1942. [Class 40 (v)] A system for measuring short time intervals particularly adapted for range determination in a radiolocation system, comprises pulseoperated means for shock exciting an oscillatory device and quenching the resultant oscillations after a predetermined time ; the oscillations, the period of which is short compared with the time interval to be measured, provide the basis for the time measurement. In the radiolocation system of Fig. 1, a master oscillator 10 controls pulse generators 14 and 20, preferably of the type described in Specification 477,875, [Group XXXV], which in turn control the modulation of pulse transmitter 16, the sweep circuit 26 for the oscilloscope 28 and the adjustable ranging unit 22 providing a range mark which is fed together with echo pulses from receiver 30 to the vertical deflecting plates of the oscilloscope via switches 11, 13. A precision sweep circuit 24 controlled by the ranging unit 22 enables a high-speed sweep to be fed to the oscilloscope through switch 25 to display on an expanded scale a portion of the range centred about the range mark. In one form of adjustable ranging unit, Fig. 2A, a starting impulse source 21 which may be the pulse generator 20 of Fig. 1, provides a series of pulses 72, Fig. 2B, at times t0, t0<SP>1>, &c. An oscillation starter and quenching timer 40 controlled by pulses 72 produces a wave such as 74 or 76 which is employed to start a precise oscillator 42 of the ringing type at time t0 and quench the oscillations at time t max, corresponding to the maximum range of the equipment, to produce the trains of oscillations 78. An amplifier 46 and feedback circuit 44 are provided to eliminate the damping effects of the ringing oscillator which may comprise a tuned circuit, a quartz crystal or a magneto-structive oscillator and may have a frequency of 100 kc/s. The wave train 78 is then passed through a phase shifter 48, of the type described in Specification 503,582, which is adjustable through 360 degrees and provides any desired phase shift such as that indicated by the wave 80, under the control of handle 52. The phase shifted wave 80 is then fed to the pulse generator 58 which produces the waveform comprising positive and negative pulses 82 and 84. In order to select one of pulses 82 as the range mark, a low-frequency oscillator 64 is shock excited simultaneously with oscillator 42 to produce the sine wave 86 which after amplification at 66 is passed through, a phase shifter 68, the phase shifted wave 88 being fed to a pedestal generator 70 which it triggers to produce the pulse 90. Phase shifter 68 is geared to phase shifter 48 so that the latter turns faster than the phase shifter 68 in proportion to the ratio of the frequencies of waves 78 and 86, and rotation of the phase shifters by crank 52 thus enables the pulse 90 to be moved over the total range from t0 to t max and to remain centred about a selected pulse 82 from the pulse generator 58. The selected pulse 82 which is thus superimposed upon the pedestal pulse can be separated to provide the single precision range marking pulse 94 which may be employed directly or fed to a fiducial mark generator circuit 60 which produces a step making wave such as 96, Fig. 2B. Fig. 4A shows a combined precise oscillator and starting and quenching circuit. The input pulse 184 at time t0, Fig. 4B, is fed via terminal 161 and condenser 162 to the grid of valye 160 which is cut off by the negative-going edge of the pulse, the voltage on the grid decaying as in curve 186 due to the discharge of condenser 162 through resistance 164, the valve commencing to conduct again at time t max as indicated in the anode current waveform 188. Oscillations 192 commence in tuned circuit 178, 180 when the input pulse is applied and are quenched when anode current flows at time t max. The oscillations are fed to amplifier 165 via condenser 182 and a coil 176 in the cathode circuit provides feedback to the tuned circuit to prevent decay of the oscillations which thus maintain constant amplitude as shown at 190. A circuit for generating pedestal pulses, Fig. 6A (not shown), comprises a valve to the grid of which are fed positive pulses derived from the timing wave. The valve remains cut off by the negative going edge of the pulse for an interval determined by the time constant of the grid condenser and resistance and produces a positive flat-topped pulse of corresponding duration at the anode. Fig. 7A (not shown) illustrates a circuit for producing a step wave from a narrow pulse 318, Fig. 7B (not shown), which corresponds with pulse 94, Fig. 2B. The narrow pulse is lengthened by means of long time-constant circuits in the-coupling circuits of two cascadeconnected valves, so that the output voltage has the desired step. In a modified ranging unit, Fig. 3A (not shown), the low-frequency oscillator 64 and its phase shifter are replaced by a resistance capacity delay circuit, Figs. 8A and 8B. A pulse 350 from the timing circuit is impressed on input terminals 352, 354 and causes condensers 356, 358 to be charged to its peak potential through diodes 361, 365. Resistances 364, 366 are large so that the amplitude 376 of the voltage 378 across resistances 364, 366 is approximately constant, while the time-constant of the resistance 360 and condenser 358 is such that the voltage on terminal 368 changes as shown at 372. Resistance 360 is adjustable so that the time T at which the voltage between the output terminals 368, 370 passes through zero can be varied and the pedestal pulse which is generated at this instance can be moved over the whole range and be employed to separate the selected precisely timed range pulse by ganging the control of resistance 360 and the phase shifter control following the precise oscillator.