Patent GB-650038-A (GB)
Title: Improvements in and relating to radio locating equipments
IPC: G01S7/06
Filed: 1947-07-16
Abstract: 650,038. Radiolocation; pulsing high frequencies. BRITISH THOMSON-HOUSTON CO., Ltd. July 16, 1947, No. 18988. Convention date, Nov. 30, 1943. [Classes 40 (v) and 40 (vii)] In order to render the time-base frequency independent of the recurrence frequency in a pulse radar system in which the echoes are displayed as deflections on a circular time base, the time-base is derived from a valve oscillator producing intermittent sinusoidal wave trains, the oscillator being rendered alternately operative and inoperative by a damping valve which is respectively blocked and conductive in synchronism with the radiated pulses. As shown in Fig. 1, the output A from a multivibrator 15 triggers a delay flip-flop 16 producing an output D whose trailing edge triggers a flip-flop 17 giving an output E which is shaped at 18 (output F) and 19 to give a trigger pulse which is applied to the transmitter 2. Echo signals from the receiver 4 are applied to an axial electrode 8 of the cathode-ray tube 9 to produce radial deflections 13 on a circular time base produced by applying push-pull outputs from a shunt-feed Hartley oscillator 20, 21, 22 directly to the vertical plates 10 via amplifiers 24a, 24b and through 90 degrees phase-shifting networks 26, 27 to the horizontal plates 11 via amplifiers 24c, 25. In order to synchronize the oscillator a waveform A<SP>1</SP> of opposite polarity to waveform A is applied from multivibrator 15 to the grid of a triode 29 which is effectively connected in parallel with one half of the inductance 20 of the oscillator tuned circuit 20, 21 so that the oscillator is alternately damped and operative during the respective positive and negative cycles of waveform A and so produces intermittent trains of oscillations. The oscillator output builds up without any delay but there is a slight delay, Fig. 2C (not shown), in the build up of the outputs from the phase shift networks 26, 27 which would cause the first few cycles of the time base to be non-circular and this is prevented by applying the output F from 18 to the grid of the cathode-ray tube which is so biassed that the trace is only visible during the positive portions of waveform F. In order to calibrate the trace the ganged switches 6, 33, 34, 35 and 35a are moved into the left-hand position thereby short-circuiting the multivibrator 15, biassing off valve 29 to permit continuous operation of oscillator 22, rendering the cathode-ray trace continuously visible and applying the output from a crystal oscillator 36 to the electrode 8 of the cathoderay tube. The frequency of oscillator 22 is adjusted to give a stationary pattern 38 so that the sweep frequency is a sub-multiple of the crystal frequency and on returning the switches to the right-hand position the duration of the " bright-up " waveform F is adjusted so that a single circular trace appears on the tube. The Specification as open to inspection under Sect. 91 states that if a plurality of equipments are used in the same locality, mutual interference can be prevented by adjustment of the delay periods E or the multivibrators may be externally synchronized through different phasing circuits from a common sine wave source. It also describes a circuit for providing range calibration pulses for a type A radar display in which a train of sinusoidal oscillations from the electron-coupled Hartley oscillator 40, 41, 42, Fig. 2 (Cancelled), is shaped by the distorting amplifier 49 and differentiated by the LR and CR circuits 50, 51 and 52, 53 to give a peaky waveform 54, 55 whose positive peaks are selected and inverted by the biassed valve 57 giving negative pulses 58 which are applied to the deflector plates of the cathoderay tube. The oscillator 42 is damped by the normally conductive triode 43 connected in parallel with the inductance 40 and the damping is removed for the duration of the time base by applying a negative pulse to the grid of 43. This subject-matter does not appear in the Specification as accepted.