GB630616A - Improvements in or relating to radar systems - Google Patents

Abstract

630,616. Radiolocation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Dec. 4, 1946, No. 35953. Convention date, July 31, 1941. [Class 40 (vii)] In order to measure very short ranges in a pulse radar system with a type-A cathode-ray. tube display, a very high-speed time-base synchronized with the radiated pulses is applied to the X plates of the tube and both the direct R.F. wave pulses and the R.F. echo wave pulses are applied without rectification to the Y plates so that the R.F. waveform of the pulses is visible on the screen and provides a timing calibration, the time of reception of the leading edge of the echo pulse being indicated by a change in the amplitude of the waveform displayed. Switching means are also provided for converting the system to give a conventional type-A display when measuring longer ranges. In the pulse altimeter shown in Fig. 1, the output from a transmitter 3 controlled by a pulse generator 1 is applied to the transmitting aerial 13 and a portion of the output is also applied to a detector and limiter 19, Fig. 4 (not shown), to produce a very high speed sweep voltage which is applied through amplifier 21 and switch 7 to the X plates of the cathode-ray tube 11 and the direct wave pulse received on a separate aerial 25 is applied through the R.F. amplifier 23 and switch 27 to the Y plates 29 to produce a timing trace 39, Fig. 3. At very low altitudes the echo pulse will be received before the direct pulse has terminated and the overlapping portions of the two pulses will produce a resultant waveform 41 of greater or less amplitude than the waveform 39 depending on the relative R.F. phase of the overlapping pulses, the point where the amplitude changes indicating the altitude. ' The rate of change of altitude may be determined by observing the rate of change in the amplitude of the resultant waveform 41 caused by changes in the R.F. phase of the echo pulse with changes in altitude. At greater altitudes the ganged switches 7 and 27 are operated to connect a slower speed sweep generator 5 synchronized by the pulse generator 1 to the X plates, the direct and echo pulses being applied through a superheterodyne receiver 31, 33, 35 to the Y plates to give a conventional type-A display. In a modification the fast sweep is produced by amplifying the initial portion of the slow sweep.