Patent GB-622098-A (GB)
Title: Improvements in or relating to apparatus for the location of distant objects
IPC: G01S15/46
Filed: 1945-03-21
Abstract: 622,098. Radiolocation; sawtooth circuits. TRICKER, R. A. R., and WRIGHT, C. S. March 21, 1945, No. 7201. [Class 40 (vi) and 40 (vii)] A pulse radiolocation apparatus for measuring the height of a distant object above the horizontal plane has a cathode-ray tube indicator scanned linearly at the pulse repetition frequency and at a speed proportional to the sine of the angle of elevation of the beam, thus providing a uniform height scale. The tube may be similarly scanned in a perpendicular direction at a speed proportional to the cosine of the angle of elevation to produce a uniform horizontal distance scale. In Fig. 1 the antenna A is used for both transmission and reception and is arranged in its mounting M to scan vertically, and is coupled to the search coil in a goniometer G whose fieldcoils are connected to the vertical time-base and the horizontal timebase generators respectively, providing a vertical scan proportional to the sine of the angle of elevation # and a horizontal scan proportional to cosine #. Both these scans commence simultaneously with the transmitting of a pulse and at the same time the cathode-ray beam is switched on at low intensity. The received echo pulse is used to modulate the beam to produce an indication B from which the height and horizontal distance to the object may be read on the scales marked on the tube. Electrostatic deflection may be used if desired and extra deflecting means provided to bring the origin to the bottom lefthand corner of the tube. Fig. 2 is a circuit diagram of suitable time-base generators for the above system. The goniometer G has its search coil fed with alternating current of any suitable frequency. Induced voltages in coils S1 and S2, proportional to cos #, are rectified by diode D1 and the voltage across the loadresistor R1 is smoothed by C1 and charges C2 through resistor R2. The voltage across C2 and R3 is amplified by V1 and fed to output valve V2 having the horizontal deflection coil L1 in its cathode circuit. Similarly the output of coils S3 and S4, proportional to sin #, is used to feed vertical deflection coils L2. The condensers C2 and C4 are also connected to clamping circuits including triodes V5 and V6, V7 and V8, respectively. The potential of the cathode of V6 and V8 is adjustable by means of a potentiometer P2 across a stabilized source of negative potential. Normally V5 and V6 are conducting and form a potentiometer which is so adjusted as to maintain the live end of C2 at earth potential. Similarly V7 and V8 maintain C4 at earth potential. On the transmission of a pulse the leading edge of a negative square wave is applied through condensers C5 to the grids of V5-8 making these valves non- conductive and thus allowing sawtooth waveforms to be produced in the deflection coils. Additional clamping circuits including V9 and V10, and V11 and V12, also controlled by the negative square wave, are similar to those previously described and are used for D.C. restoration to ensure a stable zero. Variable resistances R3 and R6 are used to allow an adjustable fraction of the square wave to be mixed with the sawtooth waveforms to obtain linearity in the current wave supplied to the scanning coils. The invention may also be employed in acoustic object-locating systems.