Patent GB-582228-A (GB)
Title: Improvements in radar apparatus
IPC: G01S7/282
Filed: 1944-06-21
Abstract: 582,228. Radiolocation; valve circuits. WESTERN ELECTRIC CO., Inc. June 21, 1944, No. 11838. Convention date, June 22, 1943. [Class 40 (v)] [Also in Groups XXXV and XXXVI] In a pulse radar system, one of a series of timing pulses generated in the radiated pulse interval period initiates the generation of a gate pulse which selects the succeeding timing pulse which is used as a range marker by bringing it into coincidence with an echo pulse. A vernier cathode-ray tube is provided, the time base of which is initiated at the commencement of the gate pulse. In Figs. 1 and 1A, synchronising pulses a for the transmitter 10 and range unit 19 are produced in the pulse generator 15 from the sine wave output of the master oscillator 14. The synchronising pulses are applied to a multivibrator 16 to produce the wave form band the negative portion 17, corresponding to the " active" period during which echoes are received, produces a damped wave train c in the timing wave generator 20. The phaseshifted wave train d from 21 is converted into alternate positive and negative timing pulses e in the generator 22 and applied together with the square wave b to the R.C. delay circuit 23 where the square wave is converted into an exponential rising voltage 130 applied to the grid of a normally biassed-off mixing valve, the timing pulses being applied to the cathode so that the valve becomes conductive at a point 33 determined by the rate of the exponential rise. The rate of increase of the voltage 130 is controllable and this control is ganged with the phase shifter 21 so that the point 33 may be varied continuously within the active period. The mixing valve produces a negative wave-form which is shaped in the generator 25 to give a short saw-tooth wave h which is fed through the sweep amplifier 35 to the X plates of the cathode-ray tube 30, and a short positive gate pulse g which is fed, together with the timing pulses e, to the grid of the " step " generator 28, Fig. 1A, i. This circuit includes a gate valve which is so biassed that only positive timing pulses coincident with the gate pulse are passed and the width of the gate pulse is such that only the first positive timing pulse 26 following the negative triggering timing pulse is passed. The transmitted timing pulse is then shaped to a step wave j in the output circuit and applied to the Y plates of the cathode-ray tube as a range marker. In a modification, the pulse form is maintained and used as a range marker and to control a means for automatically adjusting the phase-shift system to maintain the marker pulse in coincidence with the echo pulse. The amount of phase shift is shown-on the indicator 33 which is calibrated in range units. Thermionic valve circuits, Figs. 1A, 2, 3 and 7. The synchronising pulse generator 15 comprises a gas discharge triode 62, A.C. voltages being applied to the grid and anode from the master oscillator 14 in such phase that the grid reaches its striking voltage when the anode voltage is near its positive peak and negative pulses produced by the subsequent discharge of condensers 65 and 77 are fed to the magnetron 71 and the single-stroke multi-vibrator 16. The latter comprises a double triode 40 with the grid of triode 40b directly coupled to the anode of triode 40a. Triode 40a is normally conductive and triode 40b non-conductive, but on receipt of a negative pulse a on the grid of triode 40a these conditions are reversed for a period depending on the time constant R1, C8, at the end of which conditions are restored to normal until receipt of the next pulse. The output wave form b is fed to the timing wave generator 20 comprising a pentode 53 with a temperature-controlled tuned circuit L1, C15 in the common portions of the anode and screen circuits. The negative portions of wave b cuts the valve off and shock excites the tuned circuit to produce a damped wave train c which is applied to the phase-splitter valve 54 to produce a balanced push-pull output for the phase shifter 21 (see Groups XXXV and XXXVI). The frequency of the wave train is adjusted by the pre-set condenser C2 in the grid circuit of valve 54, the outputs from which are balanced to earth by equalising the anode and' cathode loads R19+R20 and R17+R18, tapping the two outputs at corresponding points on the loads, balancing out the shunt effect of the screen resistor R22 across the cathode load by means of the shunt resistance R16 across the anode load, and correcting the capacitative unbalance of the anode and cathode to earth by means of the condenser network C1, C17 and C20. The output d from the phase shifter is amplified by the R.C. coupled pentodes 91, 92, high input impedance being produced by the 2-megohm grid leak R29 and the negative-feedback resistance R33 connected between the anode of valve 92 and the cathode of valve 91. The amplified wave train is applied to the pulse generator comprising valves 93 and 94, of which valve 93 has a high cathode bias R40 (10K) and valve 94 is highly conductive due to its cathode being returned directly to earth and its grid leak R44 to H.T. +; hence, the positive half-cycles are passed by valve 93, squared-off in valve 94, and fed as timing pulses e to the R.C. delay circuit 23 and step generator 28 after differentiation in the circuits C47, R59 and C57, R75. R.C. delay circuit 23. The wave form b from the multi-vibrator 16 is fed to the grid of valve 95, the H.T. supply for this valve being held at 200v. by the voltage stabiliser 100. The negative portion of wave-form b cuts off valve 95 and the condensers C41 and C43 discharge through the variable resistance R52 giving a controllable exponential voltage rise at the anode of valve 95 which is directly coupled to the cathode follower 96, the output from which is applied to the grid of the mixing valve 98 which is biassed at a voltage Eo, developed across R56 and R57, below the stabilised H.T. Timing pulses from the generator 22 are fed to the cathode of valve 98 which is biassed at a voltage Eo/#, developed across C46 in parallel with R57, below the stabilised H.T. As the grid voltage rises, curve 130, Fig. 7, the cathode voltage is held constant, curve 131, since although the voltage at the junction of resistances R56 and R57 is also increasing, curve 132, the voltage across the condenser C46 is held constant by the diode 97. When the grid potential approaches the cathode potential sufficiently close, a negative timing pulse 33 causes valve 98 to conduct and the subsequent flow of valve current through resistance R59 discharges the condenser C46 causing the cathode potential to rise with the grid potential so that successive negative timing pulses cause successive drops in the anode voltage to produce the wave-form 134. This wave-form is applied to the double triode amplifier-distorter 101 to give a negative pulse which is applied through the short time-constant circuits C53,R68 and C55, R73 to the time base generator valve 102 and the gate pulse generator valve 103. The resistance R65 attenuates any pulses fed through the inter-electrode capacities of valves 98 and 101. The grid leak R68 of valve 102 is returned to H.T.+ causing appreciable current to flow through the high cathode resistance R70 (50K) and on receipt of the negative pulse the valve is cut off and C52 discharges through R70 giving a negativegoing saw-tooth voltage h which is fed to the sweep amplifier 35 after D.C. restoration by the diode anode 111 of valve 103. The grid leak R73 of valve 103 is also returned to H.T+ causing it to pass heavy current and the negative pulse cuts the valve off producing a short positive gate pulse g at the anode of valve 103 which is fed to the grid of the gate valve 116 after D.C. restoration by the diode anode 112 of valve 103. Timing impulses e from the differentiating circuit C57, R75 are also fed to the grid of the gate valve 116 which is normally biassed off by the potentiometer R76, R79 so that only the first positive timing pulse occurring during the period of the gate pulse g is passed. The R.C. network in the anode circuit of valve 116 converts the pulse into a step wave j which is applied to the Y plates of the cathode-ray tube 30 as a range marker. In a modification, Fig. 4 (not shown), the time base generator is omitted and the sharp pulse form is retained in the anode circuit of valve 116. Suitable values for all components are given. U.S.A. Specifications 2,004,613 and 2,063,342 are referred to.