Patent GB-652666-A (GB)
Title: Pulse-signal translating system
IPC: G01S1/02
Filed: 1948-06-29
Abstract: 652,666. Radiolocation ; valve circuits. HAZELTINE CORPORATION. June 29, 1948, No. 17448. Convention date, July 11, 1947. [Classes 40 (vi) and 40 (vii)] In a pulse radar system comprising means for continuously following an echo signal in range by a gating circuit, means are provided for causing the gating circuit to search in range in a plurality of discrete steps, the timing of the gating pulses remaining constant for the duration, equal to that of a plurality of exploring- pulse cycles, of each step, and to follow a received signal if more than a prescribed number of echo pulses is received at any one step. By this means, the risk of incorrect operation of the apparatus by spurious signals is considerably reduced. The system comprises a master oscillator 10, operating at 150 c/s., which initiates the transmission of exploring pulses A, Fig. 2, from the common T-R aerial 13. The oscillator 10 also synchronizes the production of a saw-tooth waveform B in generator 51, the output of which is applied via diode 50 to circuit 53. A delay bias is applied to the cathode of diode 50, whereby the saw-tooth waveform C as applied to the circuit 53 is delayed by a time t. Circuit 53 generates a step waveform D from which a synchronizing-pulse signal E is produced and applied to gate-pulse generator 30 which delivers wide and narrow gate-pulses P1 and P2 to gated amplifiers 21 and 33 respectively. These two gated amplifiers are substantially identical, the gating action being performed on the suppressor grid of the input pentode stage to the control grid of which the received pulse signals are applied. The apparatus also comprises a relaxation oscillator 40 comprising a condenser 41 charged through a resistor 42 and periodically discharged by gas-filled valve 43. Negative pulses are produced at the anode of valve 43 at the rate of 10 per second and these are applied via diode 44 to step-charge the condenser 66 which is connected between anode and control grid of valve 65 to provide a Miller integrating circuit. The potential at the cathode of cathode follower 62, and thus at the cathode of diode 50, rises in a series of steps, each step lasting for fifteen cycles of pulse transmission. Thus for a period encompassing fifteen transmitted pulses, the bias on the cathode of diode 50 will be such that the saw-tooth waveform applied to circuit 53 is delayed by a time t ; however, during the period comprising the fifteen successive transmitted pulses the saw-tooth waveform will be delayed by a time t2 thus giving rise to differently delayed synchronizing and gate pulses as indicated in Fig. 2 by the dashed curves. This process is repeated until the potential at the cathode of valve 62 reaches such a value that valve 71 conducts to actuate relay 70 which then discharges the condenser 66. The delay of the gating pulses P1, P2 with respect to the transmitted pulses thus increases in a series of steps until the relay 70 is actuated, when it returns to a low value and the process commences afresh. When a received pulse signal coincides with the wide gate P1, a positive output signal from the amplifier 21 is applied to the counter circuit 90. The signal is applied via cathode-follower 91 and diode 92 to charge the condenser 96 which comprises, together with pentode 97, a Miller integrator. Should the received signals be spurious it is unlikely that during any one period of fifteen transmitted more than four pulses will coincide with the wide-gate pulse. It is therefore arranged that, when five pulse signals have been applied to the condenser 96, the potential at the grid of valve 99 will fall to such a value as to cut the valve off, thus causing the contact 100a of the relay 100 to open and preventing the relaxation oscillator 40 from functioning owing to the large negative value of the bias voltage Ec2. Under these conditions the oscillator 40 ceases to control the charge on the condenser 66 and the delay introduced by the bias on the diode 50. The pulse output from the amplifier 21 is applied as a negativegoing signal via diode 63 to step-charge condenser 66, thus altering the delay bias on diode 50 until the narrow-gate amplifier 33 also applies signals, which are arranged to be positive-going and of larger amplitude than the negative-going signals via diode 64 to maintain the received echo signal in a fixed time-relationship with respect to the gating pulses. The potential at the cathode of valve 62 is then a measure of the range of the echo-producing signal and is measured by meter 84 which is calibrated in range. In order to ensure that only pulses received during one cycle of operation of the oscillator 40 are used to charge the condenser 96 at any one time, means are provided for resetting the counter circuit with each discharge of the condenser 41. When condenser 41 discharges, a negative pulse is applied to the suppressor of pentode 97, cutting it off, whereby the anode, and thus the grid, potential rises, and the condenser discharges through the grid-cathode path of the pentode. The circuit is then re-set to receive charging pulses from the amplifier corresponding to the successive range-step. It is stated that the radar system may co-operate with one or more responder beacons. The exploring pulse signal may comprise a pair of pulses coded according to spacing, each beacon being responsive only to a predetermined spacing of the exploring signals. Specification 593,346 is referred to.