GB581696A - Improvements in or relating to directional radio systems - Google Patents

Abstract

581,696. Radiolocation ; pulse generating, amplifying and shaping circuits. HODGKIN, A. L. Sept. 16, 1943, No. 15242. [Class 40 (v)] In a pulse radiolocation equipment, particularly for use on aircraft to locate other aircraft, a narrow beam is caused to scan a substantially conical field of observation in alternately diverging and converging spiral paths, and echo signals from an object within the field are applied to a cathode-ray tube having a radial time-base which is rotated in synchronism the transmitter beam and is rendered visible by the echo signals to indicate the range and bearing of the object. General arrangement, Fig. 1. A control unit 1 (shown in detail in Fig. 4) supplies (1) switching pulses to a modulator 3 to control the transmission of pulses from a short-wave generator 11 ; (2) a sine wave of 2500 cycles per sec. to the rotary coil R of a phasing unit 5 ; (3) switching pulses to the receiver 7 to condition it for reception; and (4) switching pulses to the control grid of the cathode-ray tube 8 to condition it so that a reflected pulse will cause the beam to become visible. The same aerial system, comprising a dipole and parasitic reflector DA within a parabolic reflector P, is used for transmission and reception, being connected to the receiver 7 through a mixer 10 incorporating means for preventing substantially all of a transmitted pulse from passing to the receiver. Scanning. The reflector P is pivoted to a shaft M which is continuously rotated by a motor MO. The reflector is also mounted on arms A carrying rollers R riding on a cam C which is also continuously rotated by the motor MO through a coaxial shaft M1, but at a slightly lower speed. The main axis of the reflector is thus tilted to and fro through an angle of Π30 degrees producing a spiral sweep of the transmitted beam. A more detailed description of driving means for the scanner is described in Specification 580,170. Cathode-ray tube, Fig. 5 ; display indications. The rotor R, Fig. 1, of the phasing unit 5 is rotated in synchronism with shaft M, Fig. 2, and the stator coils S1, S2 produce sweep currents in quadrature, each of a frequency of 2500 cycles per second modulated at the frequency of rotation of the reflector. These sweep currents are applied through transformers TX, TY, Fig. 5, each having two secondary windings connected as shown to the tube anode A, to the deflector plates X, Y and to centring resistances R10, R13. The cathoderay is thus deflected radially once for each pulse period, the radius of deflection rotating with the axis of the beam. Two alternative amplitudes of sine wave currents are provided to give different time scales for long- and shortrange working. A short delay is provided between the start of the radial deflection and the transmission of a pulse so that the beam has reached a certain distance from the centre when the pulse is transmitted, and the portions of the transmitted pulses which leak through to the receiver cause each trace to be brightened up, thereby producing a luminous reference circle 0, Fig. 6B. The conditioning of the receiver by control unit 1 is arranged so that only the last part of the transmitted pulse is effective, thus providing a very sharp reference circle. The echo pulses will be effective in brightening a number of radial traces to produce an arc such as ET, the distance between this and the reference circle indicating the range, the position of the arc relative to the centre indicating the disposition of the object relative to the aircraft and the length of the arc indicating the divergence between the direction of the object and the line of flight of the observing aircraft. When the object is directly ahead, the arc ET becomes a second circle. Control unit, Fig. 4. The basic control frequency of 2500 cycles per sec. generated by a back-coupled oscillator V10 is fed through an amplifier V11 and transformer L18 to lead t3 and the rotor coil R, Fig. 1. The output of amplifier V11 is also fed through a phaseshifting network C63, R112, R70 to valve V12 which is normally biassed just above cut-off. Ganged switches LS1 ... LS3 modify the circuit to provide for different amplitudes of sweep for long and short ranges. Valve V12 produces clipped half sine waves which are differentiated and applied to valve V13 which is normally biassed to cut-off. The substantially square negative pulse thus produced is inverted by valve V14 and differentiated again producing a sharp pulse in the output circuit of valve V15 which is applied over lead t4 to trigger the modulator 3, Fig. 1. The output of valve V14 is also applied to trigger a valve V16, normally biassed to cut-off, producing a square-shaped negative pulse (short or long according to the range) to condition the cathode-ray tube over lead t5. The output from valve V16 is also passed to a normally-conducting valve V17 to produce a square-shaped positive pulse to condition the receiver over lead t6. Specification 555,052, [Group XXXVI], also is referred to.