Patent GB-693930-A (GB)
Title: Improvements in radar and like apparatus
Inventor: MCMULLIN TERENCE ALEXANDER
IPC: G01S1/02
Filed: 1950-12-14
Abstract: 693,930. Radiolocation; valve relay circuits; automatic gain control. MURPHY RADIO, Ltd. Dec. 14, 1951 [Dec. 14, 1950], No. 30543/50. Classes 40 (v), 40 (vi) and 40 (vii). Relates to an automatic-ranging pulse radar of the type disclosed in Specification 690,480, in which a single strobe pulse is caused to drift relatively to the transmitted pulse until it encounters and partially overlaps a response pulse when it remains locked thereto, means being provided which are operative upon interruption of the response pulses to modify the normal drift of the strobe pulse during a succeeding " memory " period not exg aceedin predetermined maximum; such modification may comprise maintaining the strobe pulse in the same relation to the transmitted pulse as it had before the interruption. In such a system, if the strobe pulse locks on to a transient interference signal the normal search for a true response is interrupted for the maximum memory period and according to the present invention this is avoided by making the memory period dependent on the number of coincident strobe and signal pulses before the interruption. As shown, strobe pulses from generator 1 are applied to a gate circuit 3 together with response pulses from a line 4 and the gated output is applied through relay contacts 6 to the drift control circuit 2 coupled to generator 1. The gated output is also applied directly and via resistor 8 to the grids of triodes 7 and 9 respectively, the valves being biased off in the absence of signals from gate 3. A capacitor 12 is coupled between the anode and grid of V9 and between the anodes of the valves is connected a polarized relay 20 operated only when the anode potential of V7 exceeds that of V9. When positive gated signals are applied to V7 and V9, the anode potential of V7 falls sharply and that of V9 falls slowly due to the long time constant of R8, C12, and if the response pulses are interrupted the anode potential of V7 rises more quickly than that of V9 and relay 20 is operated, thereby opening contacts 6 and modifying the control circuit 2 to effect the required modification of the strobe drift. Relay 20 remains energized until the anode potential of V9 is equal to that of V7 and thus the duration of energization, i.e. the memory period, depends upon the potential difference between the anodes of V7 and V9 at interruption and this depends upon the number of output pulses from gate 3 prior to the interruption. In a modification, Fig. 2 (not shown), there is generated a second wider strobe pulse whose leading edge coincides with that of the first strobe and which is applied together with response pulses to a wide gate whose output is applied to V7 and V9 in place of the output from the narrow gate. When the narrow strobe locks on a response pulse, the whole of the response pulse is within the duration of the wide strobe and this allows the production of a negative A.G.C. voltage proportional to the amplitude of the selected response pulse which is derived from a tapping on a potentiometer connected between the anode of V9 and a negative bias source, the tapping being connected through a crystal diode to earth and via a capacitor to the grid of V9 and a balancing resistor being connected between the anode and cathode of V7. A fast A.G.C. may be obtained by interchanging the components added to V7 and V9. Specification 690,480 is referred to.