Patent GB-588672-A (GB)
Title: Improvements in energy wave reflection type ranging systems
IPC: G01S19/48
Filed: 1944-11-29
Abstract: 588,672. Radiolocation. WESTERN ELECTRIC CO., Inc. Nov. 29, 1944, No. 23875. Convention date, Nov. 30, 1943. [Class 40 (v)] In a circuit arrangement for the time base of a cathode-ray oscillograph, used for instance as a radar indicator, adjustment of the timing circuit provides a range of sweep rates and, whatever the time of sweep, the timing circuit is automatically restored to its original condition. at the end of each sweep. Fig. 1 shows in block diagram form the time base of a radar oscillograph indicator, including a prepulsor 14 of which the circuit is shown in Fig. 2. The time base is quiescent until a synchronizing pulse 11 from the radar pulse modulator applied at 10 is inverted by valve 12 to produce a pulse 13 which is applied to a single-stroke multivibrator circuit comprising valves 50 and 54 and their associated components. Valve 54 is normally conducting owing to positive bias through resistor 44. Valve 50 is non-conducting as the bias due to the current from valve 54 in cathode resistor 52 is greater than the grid potential fixed by resistors 40 and 48. The negative pulse 13 drives the valve 54 to cut-off and thus removes bias from the valve 50, which conducts and the resulting voltage drop in resistor 42 also provides the grid of the valve 54 with a negative pulse which tends to hold this valve non-conducting. The valve 50 which is self-biassed and cannot cut itself off, remains conducting until cut off by a negative pulse 27 derived, as described later, from the sweep limiter. The cutting off of valve 50 reduces the voltage drop in resistor 42 and makes the grid of the valve 54 positive, thus returning the circuit to its original condition. The time constant of resistor 44 and condenser 38 are made sufficiently large to prevent the valve 54 becoming conductive before the arrival of pulse 27. Pulse 17 derived from the anode of the valve 54 is a substantially squaretopped pulse of length equivalent to the duration of the sweep and is inverted by valve 212 before being passed as pulse 19 to the adjustable sweep generator 18. This is of resistancecapacity type and the speed of sweep is varied by choosing one of a number of resistors of different values. The condenser of the sweep generator is normally short-circuited by a conducting valve which is held non-conducting for the duration of pulse 19, allowing the sweep potential to build up. The output of the sweep generator is fed to an amplifier 20 which is described in detail with reference to Fig. 4 (not shown), and which has D.C. re-insertion and negative feedback, the oscilloscope deflecting coils being included in the feedback circuit. Provision is also made for cutting off the output valve between sweeps so that full gain is available at the start of each sweep ; alternatively, if the trace is of the centre zero type a switch may be incorporated to allow current to flow in the coils between sweeps and thus to expand the centre zero point to a zero distance circle giving better separation of indications on fast sweeps. A second sweep amplifier 3 and oscilloscope 4 may be connected, if desired, to produce an additional indicator. Thefirst amplifier is also connected to a single-stroke multivibrator circuit acting as sweep limiter 22, which provides the prepulser 14 with the negative pulse 27 when the sweep potential reaches its maximum value. Pulses 17 or 19 may be utilized to control an unblanking circuit for switching on the ray of the oscilloscope during the sweep time only.