Patent GB-590494-A (GB)
Title: Radio obstacle detection system
IPC: G01S7/08
Filed: 1944-11-22
Abstract: 590,494. Radiolocation ; valve circuits. STANDARD TELEPHONES & CABLES, Ltd. Nov. 22, 1944, No. 23259. Convention date, Jan. 4, 1943, [Class 40 (v)] [Also in Group XXXVI] In a cathode-ray tube indicating arrangement for pulse radar, the oscillograph sweep potential has two rates of increase changing from a first to a second rate when the potential reaches a certain adjustable value. This may be used to give an expanded view of the range up to a certain distance from the radar apparatus on one part of the sweep whilst showing on a smaller scale on the rest of the sweep objects up to a distance beyond, which may either be fixed, or depend on the amount of sweep remaining. A reference marker may be generaated to show on the trace where the change in sweep rates occurs and if the circuit controlling the potential at which the change occurs is adjusted to cause the marker to coincide with an echo signal, the distance to the corresponding object can be accurately read off from the adjustment calibration. Fig. 2 shows the circuit of the sweep potential generator ; positive synchronizing pulses are applied at 19 through condenser 24 to the grid of valve 20 causing this valve, which is normally biassed. to cut-off through resistor 25, to conduct and discharge condensers C1,.C2 and C3. At the end of the short synchronizing pulses, the potential of line 26 begins to rise at a rate determined almost entirely by the time constant C1, R1 as R2 and R3 are large compared. with R1. Diode 40 has an adjustable negative bias, depending on the position of tap 43 on potentiometer R4, and when this bias is overcome by the rising potential. of line 26, diode 40 conducts and effectively shunts C1 with C3, the rate of potential increase of line 26 then being determined by (C1-f-C3) R1. Thus, the position of tap 43 determines at what potential the sweep changes from a fast to a slower rate of increase. The output at 48 is applied to a clipper and pulse amplifier and may be used to provide the reference marker by lifting above the datum level on the tube screen to form a step that portion of the trace which has the faster rate of increase, Fig. 4 (not shown). The output of the sweep generator is derived through line 36 and the purpose of diode 30 and its circuit is to limit the rise in potential applied. to the oscillograph to that required for maximum deflection ; bias C is adjusted so that the diode conducts when such a potential is reached. Fig. 5 (not shown) illustrates an alternative circuit for the sweep generator in which diode 40 is provided with a variable cathode resistor, the adjustment of which is ganged to that of tap 43 in such a way that the cathode resistor is a minimum, when the bias applied through tap 43 is a maximum. This cathode resistor affects the rate of potential increase after the valve conducts in such a way that at whatever potential the change in sweep rates is effected the complete sweep is made in substantially the same time ; thus, the greater the range covered by the initial high speed or vernier sweep of the radar indicator, the slower the sweep on the rest of the tube and the more condensed the indications thereon. However, unlike the display when the circuit of Fig. 2 is used, the field up to a given distance is always in view no matter how the reference marker is moved. ,