GB593510A - Improvements in radar navigating apparatus - Google Patents

Abstract

593,510. Radiolocation ; pulse generating circuits. THOMPSON, F. C. July 20, 1945, No. 18699. [Class 40 (v)] In order to compensate for slant range distortion in an airborne pulse radar with a plan position indicator (PPI), each radial timebase sweep is delayed with respect to the transmitted pulse by an amount determined by the height of the aircraft. As shown in Fig. 1, a saw-tooth voltage from the generator SG is applied to the rotary transformer RT and the outputs from the two quadrature stators are shaped to a hyperbolic waveform as described in Specification 593,491 and applied through paraphase amplifiers PA1 PA2 (V14-V17, Fig. 6, not shown) to the x and y plates of the PPI tube. The inputs to the paraphase amplifiers are normally "clamped'' by diodes CC (V11-V13, Fig. 5, not shown) which are " unclamped " by a square wave initiated by a variable-phase height marker a which is adjusted to coincidence with the ground return echoes b on a separate height tube H. Pulse - shaping circuits. The saw-tooth voltage, Fig. 2 (a) is fed to a transitron type generator TPG (V1, Fig. 3 not shown) giving a negative pulse, Fig. 2 (b and c), which synchronizes a free-running multivibrator MV (V2 and V3, Fig. 3) to give a negative triggering pulse which is fed to the transmitter modulator M and a positive pulse, Fig. 2 (d), which is inverted in a pulse transformer T1, Fig. 4, giving a negative pulse, Fig. 2 (b), which is applied to the cathode of the height-markertiming (HMT) valve V4. The triode section of this valve is normally cut-off by grid current bias and the applied pulse renders it conductive and discharges the capacitor C3. At the end of the pulse, the rise in anode voltage is delayed, Fig. 2 (f), due to the charging time of C3 through R6 and this delay is determined by the potential difference between the anode and cathode ; the maximum anode voltage is fixed by the limiter valve V5 and the cathode voltage is determined by the potentiometer VR2 (control C, Fig. 1) which therefore controls the delay. Distortion of the trailing edge of the anode voltage waveform due to the oscillation on the trailing edge of the applied pulse from the pulse transformer is prevented by the diode section of V4. The output from V4 triggers a " flipflop," V6 and V7, giving at the anode of V6 a square wave, Fig. 2 (g), the duration of which is controlled by the potentiometer VR2 and which is converted to a negative and positive pip, Fig. 2 (i), coincident with the leading and trailing edges by the pulse-forming line LC. The pips are inverted by the transformer T2, Fig. 2 (j), and applied to the negatively-biassed cathode follower V8 which passes the positive pip, Fig. 2 (k), for use as the height marker. One output is applied to the left-hand x plate of the height tube H which is supplied by a vertical time-base from the saw-tooth generator SG, the echo signals being applied to the other x plate, and the potentiometer VR2 is adjusted to make the height marker a coincident with the first ground return b. Another output is applied to trigger a phantastron (V9 and V10, Fig. 5, not shown), of the type disclosed in Specification 582,758 which produces negative and positive square waves, Figs. 2 (l) and (m), which are applied to the anodes and cathodes respectively of the clamping diodes rendering them non-conductive and thereby allowing the hyperbolic time-base to be generated for the duration of these square waves.