Patent GB-583478-A (GB)
Title: Improvement in or relating to radar and like systems for detecting and locating objects
IPC: G01S1/02
Filed: 1943-10-15
Abstract: 583,478. Radiolocation ; valve circuits. WATSON, D. S., and WRIGHT, C. S. Oct. 15, 1943, No. 16927. [Class 40 (v)] In a radiolocation or similar echo detection system in which the transmitted beam rotates or oscillates in azimuth and a cathode-ray tube plan position indicator is employed, signals from selected bearings are displayed as deflections on a linear time-base (A scan) on a second cathoderay tube together with time measuring indications in the form of adjustable strobe markers, for the accurate measurement of range. In the arrangement described, two class A scans, A and B, Fig. 2a, corresponding to two selected bearings, are displayed on the same cathode-ray tube while in the intervals between the scanning of the selected bearings two traces a and b with variably timed strobe pulses produced in known manner are alternately displayed. The strobe pulses which are arranged to be brightened are aligned with the signal deflections, the range of the object producing the signal being determined from the setting of the strobe timing control. The cathode-ray tube screen is arranged to have a long after-glow to enable the strobe pulse to be aligned with the signal and the after-glow may be of a different colour from the direct excitation so that colour filters may be employed to view the after-glow of the signals and the direct excitation due to the strobe pulses. Selection of bearings.-Adjustable contacts 5, 6, Fig. 3 (not shown), mounted on a disc 1 which is rotated in synchronism with the aerial system, bridge contacts 9, 10 on a disc 8, the angular position of which is adjustable, and socause operation of a relay for a short interval when the aerial is scanning a small selected arc, the duration of the relay operation depending upon the spacing of contacts 5,. 6. Operation of the relay causes signals to be presented on the A scan together with necessary shift voltages, while when the relay is not operated, the strobe pulses are displayed with a lesser magnitude shift voltage. The arrangement of rotating contacts and relay is duplicated for a second selected bearing, while the A scans displaying the strobe pulses are displayed alternately at a frequency of 25 c.p.s., with necessary shift voltages. Time-base and signal circuits, Fig. 5. Valve V4 and the screen grid portion of valve V5 operate as a flip-flop circuit, the external synchronizing pulse, amplified in valve V3, rendering valve V5 non-conducting so that condenser C2 commences to charge exponentially through resistances R2, R3. Valve V2 is normally cut off until the rising voltage across condenser C2 which is fed to the grid and is D.C. restored by diode V1 renders it conducting, the resulting fall of anode voltage being fed through condenser C3 to cause the flip-flop circuit to revert to its normal condition and end the rising sweep voltage across condenser C2. The sweep voltage at the grid of valve V2 is fed through a network comprising resistances R6, R7 and condenser C4 for accentuating high frequencies, to the push-pull amplifier V7, V8, the oppositely phased outputs from which are D.C. restored by diodes V9 and V11 and fed to the X-plates of the cathode-ray tube to produce the time - base traces for the A scans. Resistances R8 and R9 are equal and as the gain of valve V8 is large, the voltages appearing at the anodes of valves V7 and V8 are necessarily equal and opposite. For producing a small horizontal shift of the time-base traces for -use with known " split " technique, a valve V10 has applied to its suppressor grid a positive pulse, coincident with the scan voltage and derived from the timebase circuits, which is D.C. restored by diode V1 and condenser C7 so that the valve is only conducting during the period of the time-base scans. A portion of the corresponding negative wave at the anode of valve V10 derived from potential divider R10 is fed to the grid of valve V8 to shift the scan horizontally by a small amount. A negative voltage fed to the grid of valve V10 prevents this action occurring so that by applying a suitable wave form to the grid of valve V10 (obtained from the aerial beam switching mechanism) the A scans can be shifted horizontally when required to give a side-by-side display. Valves V20, V21 and V23 form a normal video amplifier fed with signals, the output from valve V23 being fed through condenser C14 and relay contacts to either the Y1- or Y2-plate of the cathode-ray tube depending upon the bearing from which they are received. The gain of the amplifier is controlled by varying the feed-back resistance R17. D.C. restoration is provided at the grids of V20 and V23 by diodes V19, V20. The output applied to the plates of the cathode-ray tube is D.C. restored by a diode V12. Switching and scan brightening and shift circuits. Valves V13, V14 form a multivibrator operating at 25 c.p.s., the oppositelyphased square waves from the screens being D.C. restored by diodes V15 and fed to the suppressor grids of valves V16, V17 to render them conducting alternately. Strobe pulses from two strobe generators are fed to the grids of valves V16, V17 and the outputs from the anodes, consisting of oppositely phased square waves of amplitude controlled by resistance R13, with the appropriate strobe pulses superimposed, are fed via condensers C9, C10 and normally closed contacts of relays 1 and 2 to the Y1- and Y2-plates of the cathode-ray tube respectively to produce the traces a and b, Fig. 2a. Resistances R11, R12 connecting the anodes of V16, V17 are equal and therefore at their junction point only strobe pulses from one or other strobe generator are obtained. These are fed through normally closed relay contacts to the grid of valve V18 where they are mixed with a scan brightening pulse, of amplitude determined by the potential divider R14, R15, obtained from the anode of valve V4. The output from valve V18 is fed to the grid of the cathode-ray tube so that the strobe pulses brighten themselves, the brightness of the remainder of the trace being set at a lower level by means of resistance R14. When the aerial reaches one or other of the selected bearings, relay 1 or 2 is energized and the outputs from valves V16, V17 are disconnected from the Y-plates of the cathode-ray tube, the signal output from valve V23 being fed to the Y1- or Y2-plate together with a suitable shift voltage obtained from the potential divider R20. Simultaneously, the strobe brightening pulses are removed from the grid of valve V18 and the full amplitude of scan brightening pulse is applied by breaking the earth connection of resistance R14. The apparatus is stated to be applicable to a system in which the identity of a particular target is ascertained by interrogating pulses transmitted only over the desired bearing or sector, the returned identification signals obtained on the same trace as the strobe pulses. It is also stated that the height of a target can be estimated by measurement of the signal amplitudes on the A scan in relation to prepared calibration tables. An alternate mechanism for selecting the desired sector 'or bearing on the plan position indicator, is described consisting of radial lines of light on the screen of the tube which are rotated around the centre of the tube by rotation of the apertures producing the beams, the apertures being coupling to a switching mechanism by means of which the relays are energized at the appropriate instants. - The Provisional Specification also states that the accuracy of range measurement may be improved by confining the period of time presented on the A-scan to that corresponding to the range of the echo signal, for example Œ3000 yards relative to the echo signal.