GB617243A - Radio-pulse-echo device for measuring the distance of moving objects - Google Patents

Abstract

617,243. Radiolocation. SADIR-CARPENTIER. Sept. 13, 1945, No. 23642. Convention date, March 3, 1944. [Class 40 (vii)] In a recurrent-pulse system for measuring the range of moving objects, received echo signals are recorded at a relatively-slow rate and taken off from the recording medium at two spaced points, the two reproductions being applied in opposition to an indicator so that echoes from fixed objects are eliminated. The slow recording of the echo signals is effected by connecting the receiver to the recorder through a gate circuit opened only for the duration of a pulse, the point in the pulse-recurrence period at which the gate is opened being progressively moved so as to pass during a large number of periods the whole of the reflected signals. In the arrangement shown, at each transmission of a pulse from aerial 2, a pulse from transmitter 1 passes also through a variable delay network 5 to the gating circuit 9. The network 5 provides a maximum delay equal to the pulserecurrence period and comprises a number of similar sections connected to contacts engaged by a wiper 6 rotating at a speed related to the pulse recurrence frequency but much lower. Echoes of progressively-increasing range are thereby passed through the gating circuit 9. The echoes are fed to a recording device comprising a recording head 10, a travelling magnetic ribbon 11 and two spaced pick-up heads 12 and 13. The rate of travel of the ribbon 11 and the distance between the pick-up heads 12 and 13 are such that energy corresponding to echoes arriving at constant time intervals, i.e., echoes from fixed objects, is picked up simultaneously by the two pick-up heads. The energy picked up by the head 13 is reversed in polarity by a device 14 and fed to a circuit 15 in which it meets and cancels any energy picked up simultaneously by the head 13. Any energy passing through the circuit 15 corresponds to echoes which arrive at progressively changing time intervals, i.e. to echoes from moving objects and this energy is fed to the vertical deflection system of a cathode-ray tube 16, the time base of which is provided by a generator 19 synchronised with the movement of the wiper 6. Each moving object gives rise to two indications spaced apart and of opposite sign, the distance of the first from the origin representing range and the distance between the two indications giving a measure of the relative speed.