Patent GB-633096-A (GB)
Title: Improvements in or relating to radar systems
IPC: G01S13/70
Filed: 1947-02-20
Abstract: 633,096. Radiolocation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Feb. 20, 1947, No. 5045. Convention date, June 25, 1941. [Class 40 (vii)] In a pulse radar system means are provided for determining from differences between the transmitted and received pulse repetition rates the relative radial velocity of a reflecting object. The difference between the pulse repetition rates may be determined by measuring the rate of change of phase difference between the two sets of pulses. Oscillator 1 generates a signal having a frequency of 93 kc/s. which is applied through frequency divider 3 to synchronize pulse generator 5 producing 930 pulses per second. The pulses are transmitted by transmitter 7 and received by receiver 33, the output of which is applied to the radially-deflecting electrodes of cathode-ray tubes 19 and- 27. Alternatively, the output of 33 may be used to modulate the intensity of the cathode-ray beams. The outputs of units 1 and 3 are applied by phase-splitting condenser-resistance networks to the deflecting-electrodes of cathoderay tubes 27 and 19 to produce circular timebases with recurrence frequencies of 93 kc/s. and 930 c/s. respectively. The trace upon the screen of tube 19 accordingly represents' 100 miles and echo signals are displayed as radial deflections thereof at positions corresponding to the distance of the reflecting objects from the radar system. Echo signals are also displayed upon the tube 27 and, as shown, an echo signal 37 is followed by a pointer 41 which is driven through gearing 45 by a motor 43, the speed of which is controlled manually at 49. The motor speed is recorded by a tachometer 42 which may be calibrated in miles per hour to indicate the radial velocity of the reflecting object. In order to prevent confusion when more than one echo is received, means for selecting and following a particular signal may be provided. In Fig. 2 (not shown) a signal from the oscillator is applied to frequencydividing and phase-shifting circuits to generate a blanking-pulse signal at half the transmitted pulse recurrence frequency. This signal is applied in an adjustable phase relation to the range-tube to blank all except a selected echo signal in each alternate revolution of the trace, so that the selected signal appears brighter than the other signals. The blanking-pulse signal is also so applied to the circuits supplying the velocity-measuring tube that only the selected pulse is supplied thereto. An alternative velocity-measuring arrangement is used; a mechanically variable phase-shifter is driven by the motor to vary the phase of the circular time-base so that the deflection due to the echo signal is maintained stationary. In Fig. 4 (not shown) a vibrator operated at the pulse recurrence frequency applies the signal and gating pulses alternately to the radiallydeflecting electrode of the range tube. The signals are applied with such polarities that they deflect the electron beam in opposite directions. Automatic following of target. Instead of the motor speed being controlled manually, a pair of photo-cells may be placed on either side of the position on the velocity-measuring tube at which it is desired to maintain the selected echo indication. Signals generated by one or other of the photo-cells when the indication moves from the desired position control the motor driving the time-base to restore the position of the indication.