Patent GB-591898-A (GB)
Title: Pulse radio-frequency telegraph system
IPC: H04L25/49
Filed: 1944-07-31
Abstract: 591,898. Radio telegraphy. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., (Radio Corporation of America). July 31, 1944, No 14600. [Classes 40 (iii) and 40 (v)] In a radio telegraph receiver, pulse signals subject to interference and distortion are translated into rectangular signals by a trigger or pulse-reshaping circuit PR controlling a lock. ing circuit LC, whereby the signals are lengthened ; and in order to diminish the effect of atmospherics the system is rendered insensitive, by a local oscillator LO synchronized with the signals, except at the instants when signal pulses may arrive. Pulses such as those shown at 76, Fig 3, denoting the morse letter R with a static at 89, are applied by a diversity or other, receiver 5 to a gas-discharge valve 6 in flip-flop device forming the pulse-reshaper PR. They are; however, superimposed on a voltage wave 80 derived from the local oscillator LO through a phase-shifter 20, so that only pulses which coincide with crests of the wave, as at 81, rise above the cut-off grid voltage 90 and render the valve 6 conductive, whereas an atmospheric 89 occurring away from a crest has no effect. The valve 7 is rendered conductive, so as to terminate the mark, at each crest of a voltage wave 82 derived from the oscillator LO through a phase-shifter 21. The voltages 77, 78 across the cathode loads 12, 15 of valves 6, 7 are applied to the grids of valves 31, 27 respectively, in conjunction with a voltage wave 83 derived from the oscillator LO through a phase-shifter 22, the valves 31, 27 constituting a flip-flop locking circuit. The resultant voltage 84 on the grid of valve 31 initiates the marks in the outgoing signal 86, by rendering the valve conductive when the grid voltage rises above the cut-off 91 ; and similarly the grid voltage 85 of valve 27 terminates the marks when it rises above the cut-off 92. The outgoing signal 86 is taken from the cathode load of valve 34 at terminals 37. In a modification employing only two phase-shifters, Fig. 4 (not shown), the pulsereshaping circuit PR reverts automatically to the spacing condition after a time determined by its circuit constants. The locking circuit LC is controlled by a pair of valves whose anode voltages are those, 77,-78, derived from the circuit PR while their grid voltages are synchronized peaked pulses derived through a distorting circuit (comprising an over-biassed amplifier and a transformer) from the oscillator LO. In a further modification, Fig. 5 (not shown), the pulse-reshaping circuit PR is replaced by a diode rectifier which passes correctly timed pulses to a storing condenser, and a gate valve through which the condenser discharges to trip a locking circuit corresponding to LC. The gate valve is opened by synchronous distorted peaked impulses, giving access to the marking valve corresponding to 31. The same impulses are applied to the spacing valve corresponding to 27 and render it conductive unless they are overpowered by signal impulses. Synchronizing oscillator. The local oscillator LO, by which the above operations are tuned, comprises a pair of cross-coupled valves 47, 55, to which is applied by valve 59 a synchronizing sinusoidal voltage 79 derived from valve 6 by passing the square waves 77 through a lowpass fitter LP by way of conductor 95. Phase-shifting networks. Each of the phaseshifters 20, 21, 22, Fig. 1, comprises a condenser 69 and adjustable resistance 70, Fig. 2, forming the arms of a bridge with input transformer 68 and output amplifier 71.