Patent GB-581602-A (GB)
Title: Improvements in or relating to wireless signalling systems
IPC: H04B14/02
Filed: 1942-12-23
Abstract: 581,602. Wireless signalling. DIPPY, R. J. Dec. 23, 1942, No. 18287. [Classes 40 (iii) and 40 (v)] A wireless transmission system comprises a main transmitter and one or more satellite transmitters each radiating a pulse-modulated carrier, the carrier radiated by the main transmitter being used to impose a desired time interval between signals radiated by the main and satellite transmitters. The carriers may be received by an aircraft &c. and used to determine its directional bearing or position as in Specification 581,603. The pulses radiated from the main transmitter mav have double the frequency of those radiated from the satellites and may be distinguished therefrom by making every fourth pulse a double form. Each satellite station may have a cathode-ray tube for measuring the time interval between the pulses received from the main station and those radiated by the satellite. Locally generated voltages divide the time base into three parallel traces to which the calibration pulses, the " strobing " pulses and the signal pulses are automatically allotted according to their sequence in time. Main station. This comprises a stabilized master oscillator which determines the pulserepetition frequency by the use of frequency dividers. In order that each fourth pulse may be of double form, currents of frequencies 500 and 125 from the frequency divider are fed to rectifiers and shaping circuits, the pulses derived from the lower frequency being passed through a phase-adjusting circuit and then combined with the pulses of higher frequency, so that each fourth impulse is of double form, Fig. 2 (not shown). Satellite station. Fig. 1 shows the equipment at a satellite for using the signal pulses from the main station to control the radiation from the satellite. Pulses from the main station and from the local transmitter AT are picked up by the receiving aerial AR and pass from the receiver 1 (a) to one of the vertical plates of the cathode-ray tube T, and (b) through a shaping and selector circuit 2 (described later), (which eliminates the local pulse) to a unit 3 in which the pulses from the main station control a crystal oscillator, generating a frequency of 150 k.c. Part of the output of unit 3 passes through a fine phase-adjuster 6 (described later) and a frequency-dividing unit 7 (which also includes a coarse phase-adjuster) to the transmitter-modulator 8 and transmitting aerial AT. The frequency-divider provides a pulso-frequency of 250 c.p.s. (characteristic of the satellite) and the phase-adjusters determine the selected time interval between the pulses from the main station and those from the satellite. The other part of the output from unit 3 passes through a fine phase-adjuster 9 to a frequencydivider 10 (which also includes a coarse phaseadjuster). The frequency-divider 10 provides (1) a frequency of 500 c.p.s. for time-base circuits in unit 12 to provide a saw-tooth deflecting wave form for the horizontal plates X, X of the cathode-ray tube T ; (2) a frequency of 500 c.p.s. for a " strobe " unit 11 which controls a gate or selector valve in unit 2 in order to exclude the pulse radiated locally from transmitter AT, from the circuits 6, 7, 8 and 9, 10, 12; and (3) two series of pulses at 15 k.c.ps. and 150 k.c.ps. respectively which are applied to the cathode of the tube T to form a series of bright calibration or time-marker spots along the time-base trace ; these are used with the main time-base trace and the high-speed scanning voltages respectively to measure the time interval between the various pulses shown on the screen. The unit 11 (described later in connection with Fig. 5) in addition to providing slow and fast time-base potentials for the plates X (as mentioned above) also provides (1) a stepped wave-form applied to Y plate of the tube, opposite to that supplied with the received signals, to cause trace displacement into three parallel lines (see Fig. 4) ; (2) a wave-form applied to the grid of the tube to black-out the return stroke of the beam ; and (3) further wave-forms for providing movable " strobes " or markers along the main time base trace. Shaping and selector circuit 2, Fig. 1. The pulses from receiver 1, Fig. 1, are fed through resistance R2, Fig. 3, to a valve V34 which applies negative pulses to valve V35, the anode circuit of which includes a delay network, thereby producing a square-shaped pulse of 3.5 microseconds duration. This is applied through valves V36, V37 to unit 3, Fig. 1, but the passage of the pulse radiated locally is prevented by a " strobing " or timed pulse applied to suppressor grid of valve V36 via terminal t5 from units 10, 11. Phase-adjusting circuits 6, 9, Fig. 1. The input terminals AA, Fig. 4A, are connected to two networks in parallel, one comprising two resistances R1, R2 and a condenser C1 and the other two condensers C4, C5 and a resistance R3, ganged condensers C2, C3, C6, C7 applying the phase-shifted output via transformer L7, L8, valve V39 and transformer L9. Time-base and other circuits in unit 12, Fig. 1. The 500 c.p.s. current from unit 10 is led through rectifier V55, Fig. 5, to the grid of valve V56 of a relaxation oscillator to generate saw-tooth voltages by discharging condenser C8. These voltages are applied by a paraphase amplifier comprising valves V57, V58 to termina.ls t7, t8 connected to the horizontal deflecting plates X, X, Fig. 1, of the C.R. tube. The screen grid of valve V56 is connected via terminal t9 to the grid of the C.R. tube to suppress the return stroke of the C.R. beam. The 500 c.p.s. current from unit 10 is also applied at terminal t6 to a frequency-divider V54 developing pulses at 250 c.p.s. which are led in phase to the grids of relaxation pentodes V59, V60, V61 and (from the screen-grid of V54) in anti-phase to the grid of a relaxation pentode V62. The pentode V59 generates a three - step wave - form (as in Specification 581,603) which is fed from its screen grid via terminal t11 to the vertical deflecting plate Y opposite that to which the received signals are applied, thereby dividing the main time base into three parallel traces as shown in Fig. 4 to which the calibration pulses, the strobing pulses (see below), and the signal pulses are automatically allotted according to their sequence in time. The pentodes V60, V61, V62 (operating as described in Specification 581,603) deliver via condensers C31, C30 and C26 three wave-forms, separately adjustable by potentiometers R73, R74, R76,-to the suppressor grid of a flip-flop oscillator V63 (operating as described in Specification 581,603 which provides a three-pulse wave-form, repeated 250 times per second, which is applied via terminal t12 to the cathode of the tube T where it causes brightening of short portions of the main trace (see Fig. 4) at positions determined by the setting of the potentiometers R73, R74, R76 and indicated at A, B, C in Fig. 4. The same output wave-form from pentode V63 can be applied by switch ST (in place of the 500 c.p.s. wave-form from terminal t6) to the time-base generator V56 to provide high-speed time-bases corresponding to the portions of the main trace selected by the three-pulse wave-form from terminal t12.