Patent GB-430644-A (GB)
Title: Improvements in or relating to apparatus and methods for modulating, controlling or varying alternating current energy
IPC: H03C1/54
Filed: 1934-12-27
Abstract: 430,644. Phase changing. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.- (Assignees of Crosby, M. G. ; Riverhead, Long Island, New York, U.S.A.) Dec. 27, 1934, No. 37090. Convention date, Dec. 27, 1933. [Class 38 (ii)] [See also Group XL] A carrier or other alternating-current wave is modulated or varied by transmitting the wave along an artificial line and varying the terminal impedance of the line either manually or by a signal, a wave modulated or varied in phase or amplitude being picked up at a tapping-point on the line. Two such lines may be employed, with reversing-switches arranged so that the carrier wave and the signal wave may be applied in phase agreement or in phase opposition ; and the two outputs from relatively-displaced tapping-points on the lines may be combined additively or subtractively. As shown in Fig. 2, the wave from a source 1 is applied through a coupling- valve 3 to one end of an artificial line 6, the opposite end of which is closed by an impedance comprising the plate-filament path of a valve 8. The internal resistance of the valve 8 is varied by the signal voltage from the source S applied to its grid. The terminal impedance causes reflection of the wave, and sets up a stationary wave on the line 6. The voltage at any point of the line 6 is compounded of the advancing wave and the reflected wave and at points other than maxima and minima the phase of the voltage changes as the amplitude of the reflected wave is varied by variation of the terminal impedance. Thus at a suitable tapping-point 12, a phasemodulated wave may be picked up and after amplification at 10 may be transferred to an aerial through a current-limiting device. The grid-controlled valve 8 may be replaced by a triode valve with fixed grid voltage, and with the modulation voltage applied to its plate, Fig. 4, (not shown) ; or modulation may be applied to the outer grid of a tetrode valve, Fig. 6, (not shown) ; or a manuallyvariable impedance or resistance may replace the valve 8, Fig. 1, (not shown). Fig. 3 shows a duplicated arrangement of the artificial lines. The carrier from the source 1 is applied to the lines 6, 6<1> through valves 3, 31 which may be fed in phase agreement or in opposition by adjustment of a reversing- switch 22. The terminal impedance valves 8, 81 have their grid circuits coupled to the signal source S and one grid circuit includes a reversing-switch 21. The output is taken from two relatively-displaced tapping-points 12, 12<1> and after amplification by valves 10, 10<1> is combined in the coupling 11 either by way of addition or subtraction according to the setting of the switch 23. According to the selection of the tapping-points and of the switch settings, the output comprises an amplitude-modulated wave, a phase-modulated wave, or an amplitude-modulated wave with the carrier eliminated. In a further arrangement shown in Fig. 10, two tapping- points b, 12<1> are taken on a single line 6 and are connected to amplifiers 10, 10<1> which have their outputs in parallel. By selection of the tapping-points either phase or amplitude modulation may be produced. A switch K may be provided to connect one of the valves 10 to the source 1 instead of the tap b ; with this connection, adjustment of the tap 121 enables either phase modulation or amplitude modulation with or without carrier suppression, to be effected.