Patent GB-703667-A (GB)
Title: Control systems for pulse-echo target position-indicating equipment
Inventor: HIRSCH CHARLES JOACHIM
IPC: G01S13/70
Filed: 1951-10-01
Abstract: 703,667. Pulse radar valve circuits. HAZELTINE CORPORATION. Oct. 1, 1951, No. 22821/51. Classes 40 (6) and 40 (7) Relates to automatic-ranging pulse radar systems in which a pair of gate pulses automatically search for an echo pulse and then track it and wherein the gate pulses are maintained substantially stationary for a predetermined "memory" period if the echo pulse fades; if the echo pulse re-appears within the memory period normal tracking is resumed but if not the search is recommenced. According to the present invention the memory period is made dependent on the duration of the tracking period prior to failure so that 'if the gate pulses lock. into a spurious transient signal the search is only interrupted for a short period but if the gate pulses have been tracking an echo pulse for two seconds or more then the memory period is six seconds. The invention may be applied to a secondary radar system in. which the interrogator and responder transmit coded pulse pairs. As shown a positive sawtooth B, Fig. 2, from generator 51 synchronized by the master oscillator 10 is applied to the anode of a diode 50 and a positive sawtooth C having a recurrence period 300 times the pulse recurrence period is applied to its cathode from the search sweep generator 41 via relay 79, D.C. amplifier 42 and cathode follower 43, valve 77 being normally conductive so that relay coil 79" is energized and the arm 79<SP>1</SP> contacts 79b. The cathode of diode 50 is also coupled to a wave shaping and differentiating circuit 53 which produces a pulse E when the amplitude of wave B exceeds that of C, the pulse E being applied to trigger a gate pulse generator 30 producing wide and narrow gate pulses F and G without coincident leading edges which are applied together with echo pulses from 'receiver 20 to gating circuits' 21 and 31 respectively. The negative output from the wide gate 21 triggers generator 22 giving a negative pulse of longer duration than an echo pulse which is applied through diode 73 to partially discharge the positively charged condenser 74 coupled to the suppressor grid of pentode 77. When a predetermined number of echo pulses coincident with the wide gate has been received, pentode 77 is cut off to de-energize relay coil 79" and move the relay arm 79' from contact 79b to 79a thereby terminating the search. Narrow positive pulses from narrow gate 31 and wider negative pulses from pulse generator 22 are applied via diodes 60 and 61 respectively to charge and discharge condenser 62 and the system establishes an equilibrium tracking condition with the echo pulse overlapping the trailing edge of the narrow gate pulse; the potential applied to the cathode of diode 50 is then proportional to range and is displayed on a voltmeter 90. Searching may be re-initiated by returning relay arm 79<SP>1</SP> to contact 79b manually. When the valve 77 is cut off at the commencement of tracking, i.e at time t2, Figs. 3 and 4, condenser 82 which is connected in series with resistor 80 between the control grid and anode charges up to a maximum value at time t5 as shown by the full line portion of curve A, Fig. 3, and if the echo signals fail then or at some subsequent time condenser 74 is rapidly charged positively but the charge on condenser 82 decays slowly as shown by the dotted portion of curve A and valve 77 is not fully conductive until the charge decays to a level B at time t6, the time interval t5-t6 constituting the maximum memory period. If the tracking period is less than t2-t2, the charge on condenser 82 does not attain the critical value B and subsequently valve 77 becomes conductive as soon as the signal fails, i.e. the memory period is zero, and if the tracking period has an intermediate value then condenser 82 does not charge up to the maximum value and the memory period will have an intermediate value as shown in Fig. 4. The component values of the R.C. network R78, R80, R81, R84, C82 and C83 may be such that the charge and discharge periods of condenser 82 are four and six seconds respectively for a 30 c/s pulse recurrence frequency. Reference has been directed by the Comptroller to Specification 693,930.