Patent GB-741281-A (GB)
Title: Electrical signal generating circuits and improved radar display system
Inventor: BENJAMIN RUDOLF
IPC: G01S7/22
Filed: 1951-03-09
Abstract: 741,281. Pulse-generating circuits; pulse radar. NATIONAL RESEARCH DEVELOPMENT CORPORATION. March 10, 1952 [March 9, 1951], No. 5706/51. Classes 40 (6) and 40 (7). A circuit for producing a train of pulses at a predetermined interval after the beginning of a control signal, comprising a saw-tooth generator which is started by the beginning of the control signal and which causes a pulse to be produced when the instantaneous output voltage of the generator exceeds a reference value, the pulse being used to restart the saw-tooth generator and the generator being stopped at the termination of the control signal. The circuit shown is for producing range-marking pulses which in a plan position indicator combine to form concentric steadily expanding or contracting range marking rings. Basically it comprises a flip-flop (Fig. 1) triggered by the radar synchronizing pulse and which does not restore until after the final reflected pulse is received. The first part of the output pulse of the flip-flop starts a Miller-type saw-tooth generator, the instantaneous output of which rises until it is equal to a reference voltage applied to a voltage comparator, whereupon a pulse is produced which constitutes the first range-marker pulse and which restarts the generator. The circuit continues to produce marker pulses until the flip-flop returns to its original state. The delay in occurrence of the first marker pulse depends upon the initial value of the anode voltage of the saw-tooth generator and this is varied by means of a motor from one value to another to correspondingly vary the delay, causing the marker rings to contract or expand. The varying voltage is rapidly returned to its initial value when the delay gets small or approaches the pulse spacing so that the inner or outer ring respectively disappears and is replaced by a new outer ring or inner ring. In the detailed circuit (Fig. 3) the Miller sawtooth generator valve V2 is normally held fully conducting by valve V4. Each radar synchronizing pulse operates a flip-flop V1 causing valve V4 to be cut off and the Miller capacitor accordingly charges through the cathode resistor of valve V4. The anode voltage of the Miller valve rises until the voltage it feeds to the comparator V6, V7 equals a reference voltage whereupon valve V6 rapidly becomes conductive aided by feedback applied from the anode of V6 to the grid of V7 through a capacitor and diode circuit. The resulting pulse output from V7 is differentiated in a circuit T and fed, together with the radar video signal, to an output cathode follower V12, V13. The pulse from V7 also operates a flip-flop V9 which renders a valve V10 conducting. This valve is in the grid circuit of the Miller valve and when conducting rapidly restores the grid voltage to its initial value and restarts the saw-tooth. Pulses continue to be generated in this manner in the output circuit until the flip-flop valve V1 returns to its original condition. The time taken for the anode voltage of V2 to reach the reference value depends upon the initial value of the anode voltage and this is initially determined by a valve V5, the grid voltage of which is in turn controlled by the voltage from a potentiometer driven by a motor such that the voltage gradually rises or falls and then rapidly returns to its original value. Valve V5 is cut off by the output from the flip-flop V1 so that the initial anode voltage for succeeding sweeps is independent of the potentiometer and has the value corresponding to the desired range marker pulse spacing. Diodes are provided in the circuit to effect D.C. restoration of the various pulses where required.