Patent GB-598649-A (GB)
Title: Improvements in or relating to radio-locating apparatus
IPC: G01S1/02
Filed: 1943-03-30
Abstract: 598,649. Radiolocation ; valve circuits. COCKCROFT, J. D., POLLARD, P. E., NEWSAM, B., BRITISH THOMSON-HOUSTON CO., Ltd., and LUCAS, G. S. C. March 30, 1943, No. 5123. [Class 40 (v)] In radiolocation apparatus of the pulserepetition type, selected echo signals for determining range are presented against a slow time-base on one oscillograph and against a fast time-base on a second oscillograph, the two oscillographs being interlinked through common control means for giving approximate and accurate indication of the range. The control means enable a selected signal trace and a reference mark to be brought into coincidence to determine the approximate range on the first oscillograph and this operation controls the presentation of the selected trace only on the second oscillograph. To determine the bearing and elevation of the target, the echo signals are received on an aerial backed by a parabolic reflector, the aerial being driven over a circular orbit around the axis of the reflector at a constant speed so related to the repetition frequency of the exploring pulses that it passes through the four cardinal points of its orbit at instants when an exploring pulse is transmitted ; two additional C.R. oscillographs are controlled by the selected echo signal to indicate the comparative amplitudes of the signal received at instants when the aerial passes the four cardinal points. General arrangement and transmission and reception of signal pulses.-The installation is carried by a mobile cabin, Fig. 2 (not shown), comprising a rotatable compartment 5, Fig. 1, for supporting the transmitting and receiving aerials 1, 2 and their reflectors. The compartment 5 houses the circuits of the transmitter, and the receiver circuits associated with the first stage of frequency conversion. The transmitting dipole radiates a ten-centimetre wave in pulses lasting one microsecond with a repetition frequency of 400 per second. The pulses are generated by a magnetron oscillator 6, Fig. 1, and Fig. 3 (not shown), fed with rectangular pulses from a modulator circuit 9 and timing unit 10 described later. Echo signals received by aerial 2 are reduced in frequency by oscillator 16 and mixer 17, to a frequency of 65 megacycles and pass through a matching valve 18, transmission line 20, I.F. amplifiers 19, 23 and amplifier 25 to the upper electrodes of the coarse and fine range oscillographs 26, 27 and to the lower electrodes of the bearing and elevation oscillographs 41, 42. Determining range.-Locking pulses (of one microsecond duration repeated 400 times per second) derived from modulator 9 or from a small pick-up in reflector 3 are applied at terminal 29 to a unit 30 which prolongs them to 240 microseconds, the prolonged pulses actuating a multi-vibrator 31 controlling (1) a time-base circuit 32 for generating a linear sweep voltage applied to the X-plates of range oscillograph 26, and (2) a sine-wave generator 33 which is shock-excited by each pulse to generate a slightly damped train of waves passing through a phase potentiometer 34 and amplifier 35 to the X-plates of oscillograph 27. Thus, there is applied to the X-plates of tube 26 a linear sweep voltage lasting 240 microseconds (corresponding to a slant range of 40,000 yards), and to the X-plates of tube 27 a sinusoidal sweep voltage in which the duration of each half-cycle is 6 microseconds (corresponding to a slant range of 1000 yards). The linear sweep voltage from unit 32 is also applied to a selecting circuit 36 together with a steady adjustable voltage from a potentiometer 37, the circuit being designed to produce a sixmicrosecond pulse each time the sweep voltage passes through a value derived from the potentiometer 37. These selecting pulses are taken through circuit 38 and are applied (1) to the grid of tube 26 to brighten periodically the trace for a period of 6 microseconds ; (2) to the grid of tube 27 to periodically remove a cut-off bias for the same period of 6 microseconds. The potentiometer 37 is adjusted by hand to determine the timing of the selecting pulses in relation to the timing of the echo signal pulses so as to. intensify the electron stream in tube 26 and thus. produce a bright spot or reference mark which is brought into coincidence with a selected signal trace, the selecting pulses being also applied to the tube 27 to release its electron stream whereby only the signal trace selected on tube 26 can appear on tube 27. The phase potentiometer 34 is linked with potentiometer 37 so as to introduce a corresponding change of phase of the sinusoidal sweep voltage applied to tube 27, and this potentiometer is adjusted until the echo trace is accurately centred on the screen of tube 27, the slant range being read on a scale associated with the potentiometer. Detail circuits for several of the units of Fig. 1 are shown in Figs. 10, 10a, certain features of which are described in later paragraphs of this abridgment and form also the subject-matter of Specifications 598,701, and 598,702, [Group XXXV]. Determining bearing and elevation thermionic distributers.-As described above, separate C.R. oscillographs 41, 42, Fig. 1, are used for bearing and elevation, echo signals received as the receiving aerial passes through the four cardinal points being distributed to tubes 41, 42 by valve circuits 47, 48 controlled by a two-phase generator 43 driven by motor 39 synchronously with the receiving aerial. The circuits 47, 48 are also controlled by the selecting pulses, previously referred to, so that only signals from the selected target influence the tubes 41, 42. Signals received by the dipole 2 when passing through the " left " and " right " cardinal points give rise to two echo traces on bearing tube 41, whilst signals received when the dipole passes through the " up and " down " points give rise to two traces on the elevation tube 42. The echo traces on tube 41 thus represent signals picked up at two points equally displaced horizontally from the axis of the reflector and only appear at equal amplitude when this axis coincides with the bearing of the target. The same applies to the two traces on the elevation tube 42. Fig. 11 shows in further detail the circuits of the bearing tube 41. The echo signals from the receiver proper are applied via terminal 249 to plate Y1, and the two-phase currents from generator 43, Fig. 1, are applied via terminals 44, 45, 46 and transformers 234, 235 to the cathodes of the distributing valves 220, 221, 222, 223, so that the voltages on the cathodes are in phase quadrature, and the valves in turn pass current only as the dipole 2 passes through its four cardinal points, provided that a signal selecting voltage from terminal 270 is simultaneously applied to the grid of the valves. The pulses from valves 220, 221 are applied via terminal 236 to the circuits of tube 41 and those from valves 222, 223 via terminal 237 to the elevation tube (not shown). Successive pulses from valves 220, 221 are fed to the cathode 243 and, through a time-delay circuit 244, 245 to the grid of the tube, so as to release or intensify periodically the electron stream. The same pulses also develop short sweep voltages through 247, 248 applied to plate X1. The " left " and " right " echo traces would appear at the same point along the sweep, but a shift voltage, from circuits 239, 240 and terminal 241, applied to plate X2 separates the two signals by a distance sufficient to enable their amplitudes to be readily compared. Automatic gain control.-In order to emphasize the selection of a.single trace only, an automatic gain control voltage, applied to one of the I.F. amplifiers, is derived from the circuit shown in the upper part of Fig. 11. Short impulses of four microseconds duration (derived from the sinusoidal sweep voltage applied to the range oscillograph 27 and the signal selecting pulses) are applied via terminal 270 to the suppressor grid of valve 205, echo signals being applied via terminal 206 to the control grid of the same valve. When both grids are simultaneously energized, and only then, valve 205 passes current through .a diode 207 and resistance 208, which prolong the pulse before passing it to a valve 209, the output of which is fed via a diode 211 and smoothing circuit to the grid of a valve 216, the cathode resistance of which provides an A.V.C. voltage. Calibration.-The output of a crystal-controlled oscillator, and locking pulses synchronized with the exploring pulses, are fed respectively to the' control grid and suppressor grid of a valve, which thus produces a discrete train of pulses occurring at the frequency of the oscillator and lasting for the duration of a locking pulse ; these trains of pulses may be applied to the range oscillographs in place of the echo signals. Production of exploring pulses.-These are generated by a magnetron, Fig. 3 (not shown), which is periodically subjected to an exciting current of constant amplitude produced by storing and shaping networks (electrically half a microsecond long) which are charged in parallel and discharged. in series through a pair of gas-filled relays, the timing of these relays being controlled by a third gas-filled relay, Fig. 4 (not shown). Crystal mixer.-The received signals are first heterodyned with a local oscillation in a resonating chamber 17, Fig. 6, containing a silicon crystal 96 coupled through a low impedance valve to an I.F. amplifier. Scanning movement of receiving aerials.-In order that the receiving dipole may be moved in a circle around the focus of the reflector (to vary its directivity) while always remaining parallel to the transmitting dipole, the inner conductor 15, Fig. 5, of the feed line from the dipole passes through an impedance matching sleeve 88 secured to the rotor 89 of the driving motor 39 and tilted at a slight angle as shown. The conductor 15 passes through a sleeve 92A secured to a ball 92 capable of limited rotational movement