GB658686A - Calibration of radar equipments - Google Patents

Abstract

658,686. Radiolocation. BRITISH THOMSON-HOUSTON CO., Ltd., and MATON, R. W. March 10, 1949, No. 6585. [Class 40 (vii)] An arrangement for calibrating a radar set employing a cathode-ray-tube display arrangement, comprises means for applying in alternation to the display unit fixed-range markerpulse signals and variable-range pulse signals whereby the variable-range signals may be calibrated with reference to the fixed-range signals. A saw-tooth waveform A, corresponding to the sweep waveform for the cathode-ray display, and a large-amplitude oscillatory waveform B, which is derived from a circuit which is shock-excited at the instant of pulse transmission, are applied alternately by means of a continuously-operated relay R to the grid of a valve V1 which together with a valve V2 forms a cathode-coupled flip-flop arrangement. At the beginning of each sweep of the cathode-ray tube, valve V1 is non-conducting. However, as the potential applied to its grid exceeds a predetermined value, V1 conducts while V2 ceases conducting, thus shock-exciting inductance 4. By virtue of the rectifier 5 connected across the inductance, the oscillation therein is limited to a pulse comprising a single half-cycle of oscillation. This pulse is applied to amplifier 12 and thence to the cathode-ray tube 13. The potential of the grid of V1 at which the change-over occurs may be varied by means of the potentiometer 14 which varies the bias applied to the grid of V2. The timing of the variable-range pulse produced when waveform A is applied to V1 is thus controlled by the potentiometer 14; the timing of the fixed-range pulses produced when waveform B is applied to V1 is, however, sensibly independent of the potentiometer due to the large amplitude of the signal. Fig. 3 illustrates a portion of a P.P.I. display wherein fixed-range marker indications 18 and 19 occur in alternation with variablerange indications 21. By aligning the variablerange indications with the fixed-range indications, the scale 17 associated with the potentiometer 14 may be calibrated. To prevent spurious indications from being produced when the relay R changes over, an additional relay 22 synchronized therewith is provided. When the contacts of relay 22 are open, the bias potential applied to amplifier 12 rises to zero, thus preventing the normal operation of the amplifier and preventing any signals applied thereto from affecting the display.