Patent GB-582169-A (GB)
Title: Improvements in radio equipment for locating distant bodies
IPC: G01S1/02
Filed: 1942-03-24
Abstract: 582,169. Radiolocation; valve circuits. COCKCROFT, J. D., and POLLARD, P. E. March 24, 1942, No. 3925. [Class 40 (v)] [Also in Group XXXVI (Appx.)] In a radiolocation system in which separate cathode-ray tube indicators are employed for range and bearing, a particular echo signal appearing on the range indicator is correlated with its counterpart on the bearing indicator by means of a potentiometer control. A potentiometer provides a continuous indication of range by applying a biassing voltage to the deflecting system of the range C.R. tube to bring a selected signal to the centre of the screen, while a similar potentiometer ganged with the range potentiometer causes the same signal to be centred on the screen of the bearing C.R. tube Fig. 8 (not shown). Details of this form of potentiometer control are described in Specification 582,170. In the complete radiolocation system described, the transmitter Figs. 1 and 3 (not shown) which produces 3 microsecond pulses at a recurrence frequency of 1000-2500 c.p.s. comprises a push-pull master oscillator followed by a neutralized push-pull amplifier. Pulse length is controlled by " squegging " action in grid circuit of the oscillator which is normally biassed off and caused to transmit by pulses from the modulator unit, Fig. 2 comprising the recurrence frequency blocking oscillator V1 followed by shaping amplifiers V2, V3 and the cathode followers V4, V5. The positive pulse from terminal 31 is fed to the master oscillator grid circuit, diode V8 providing a path for reverse grid current in the oscillator and diode V7 preventing flash-over. The recurrence frequency is controlled by adjustment of the grid circuit resistance of the blocking oscillator V1. The transmitter preferably operates on one of two preset frequencies, the aerial comprising a telescopic half-wave dipole being coupled through matching stubs and a feed line to a change over switch ganged with the wave change switch. The aerial which is arranged for rotation through approximately 90 degrees may be used at two different heights. The performance of the t ansmitter is supervised by a monitor cathode-ray tube, one pair of plates being fed via an attenuating line with energy tapped from an R.F. choke -in the aerial circuit while the sweep voltage for the other plates is derived from the circuit comprising valve V6 and condenser C 10, and the blackout removal pulse is obtained via terminal 30 from the cathode of valve V4, in the modulator unit Fig. 2. The receiver, Fig. 4, comprises two separate signal channels, one fed from the Range aerial comprising a dipole and keyed " sense " reflector and feeding the Range C.R. tube indicator, while the other channel is fed from the Bearing aerial comprising a pair of spaced dipoles fitted with reflectors and coupled through a phasing box, and feeds the Bearing C.R. tube indicator. A common local oscillator for both channels feeds one mixer directly and the other through a buffer amplifier to prevent the transfer of noise from the range to the bearing channel. The input circuits of the first R.F. stages, Fig. 5 (not shown) comprise semi-aperiodic transformers resonating with the valve capacities at the middle of one wave range, series capacity being switched in for the other range. The remaining R.F. stages are permeability tuned, the core movements being controlled by a common cam while the coils are in two sections, wave-range switches being ganged to the tuning control. The local oscillator is tuned by a separate cam and waverange switching is avoided by using a high local oscillator frequency on one range and a low frequency for the other range. The 4,000 volt range time base and 2000 volt bearing tube time base and the back stroke elimination circuits are controlled by a relaxation relay circuit, Fig. 6, triggered by pulses from a locking receiver. Valves V3A, V3B, form a biassed multivibrator which is triggered by the locking pulse amplified in V2B and V2C to produce a negative-going 300 microsecond pulse at the anode of V3A. This pulse cuts off the time discharger valves V5A, V5B thus' permitting the time base condenser, Fig. 8 (not shown) which is connected via terminal 39, to charge up and produce the 300 microsecond sweep, valves V4A, V4B, provide back-stroke elimination voltages to the range and bearing cathode-ray tubes through terminals 41 and 42. The negative pulse from the anode of valve V3A is also fed via condenser C10 and terminal 37 to cut off the discharge valve in the range time base circuit, Fig. 7 (not shown). The normal time base provides a range of 14,000 yards but by switching in a series resistance in the time base supply ranges up to 30,000 yards may be accommodated on the C.R. tube screen, signals on the range and bearing tubes being correlated by means of mechanical pointers. To enable the range potentiometer to be adjusted to read accurately by means of trimming condensers in the range time base circuit, a calibrator producing oscillations of period corresponding to 1000 yard intervals is employed. A 164 kc/s. crystal oscillator V12B, Fig. 9, and a blocking oscillator V3D generating 300 microsecond positive pulses with a recurrence frequency of about 1000 c.p.s., are coupled to the control and suppressor grids respectively of a mixer valve V2D. The output of V2D, consisting of 300 microsecond trains of 164 kc/s. oscillations, is fed through terminal 33 to one X-plate of the range tube and also through terminal 34 and terminal 35 (Fig. 6) to trigger the range time base so that a stationary pattern is produced on the screen of the range tube. When the Calibrator switch 40 is " off the range time base is triggered normally by the output from the lock line 36. The circuits of the cathode-ray tubes and their interconnections and the relation to earth potential of the associated power supplied, time base circuits, and potentiometers, are illustrated in Fig. 10 (not shown).