GB597052A - Improvements in circuits for measuring short periods of time - Google Patents

Abstract

5 9 7 , 0 5 2 . Valve circuits; radiolocation. PLETTS, J. W. May 2, 1945, No. 11199. [Class 40 (v)] [Also in Group XXXVI] A pulse radar system comprises a time-base circuit wherein the sawtooth time base voltage is applied differentially with the output from a potentiometer to the deflecting plates of the cathode ray tube, the setting of the potentiometer indicating the range from which is received an echo signal appearing at the centre of the trace, and wherein the rate of change of time base voltage is controlled by an adjustable datum voltage which is also applied to the potentiometer so that the rate of change of time base voltage may be altered without upsetting the correlation between the potentiometer setting and range. A pulse waveform 25, which is synchronized with the exploring pulse, is applied to the suppressor grid of a pentode 20 which is normally cut off. At the instant of transmission the pentode conduits and, due to the Miller timebase circuit comprising condenser 22 and resistor 23, its anode voltage falls at a nearly constant rate, proportional to the " datum " voltage on line 24, the total amplitude of the sweep voltage being nearly equal to the " supply " voltage on line 26. The saw tooth waveform from the anode of the pentode 20 is fed to one X-plate 28 of a cathode ray tube, the other plate of which is connected to ground. The voltage of the plate 28 is initially that of the slider of potentiometer 32 and falls from this value by nearly the whole of the supply voltage at a constant rate. The potentiometer slider is set so that the received echo is displayed at the centre of the cathode ray tube screen, so that the echo time is equal to the time taken for the time base voltage to fall by the voltage at the potentiometer slider. Both the rate of change of the time base voltage and the potentiometer voltage are proportional to the datum voltage on line 24, and thus the switch 35 may be opened and closed without affecting the potentiometer setting corresponding to any particular echo time. With the switch closed, the time base voltage falls at a high rate, so that the trace on the cathode ray tube corresponds to only a short element of the total range, and even with the potentiometer set for maximum range, the echoes which can be received on the screen are from comparatively near objects. However with the switch open the voltage falls at a much lower rate, so that, although echoes appearing at the centre of the screen are, for the same potentiometer setting, from the same range as before, an echo from a considerably greater distance can be seen and its range estimated. Specification 582,170 is referred to.