Patent GB-484626-A (GB)
Title: Improvements in or relating to electron discharge devices and circuit arrangements
IPC: H03B13/00
Filed: 1937-04-06
Abstract: 484,626. Cathode-ray tubes ; modulating systems. MARCONI'S WIRELESS TELE - GRAPH CO., Ltd. April 6, 1937, No. 9770. Convention date, April 6, 1936. [Classes 39 (i) and 40 (v)] In frequency or phase modulation of a carrier frequency, the modulation is effected by means of a cathode-ray tube whose output electrodes or target 10 consists of spiral plates 14, 16, Figs. 1 and 2 ; the beam from the gun 4 in its undeflected state impinges on the neutral centre o of the target, but when deflected traces circles C<1>, C<2>, C<3> on the target the size depending on the potential applied to the plates 6, 8. These pairs of plates are at 90‹ and deflecting currents in quadrature are supplied to them ; but the angle between the pairs of plates may be other than 90‹ the currents being also in corresponding phase relationship. There may be four or more spiral target plates 14, 14<1>, 16, 16<1>, Fig. 2a, the pairs being interconnected ; the surface of the target may have a coating of luminescent material to assist in monitoring and a closed ring may surround the target for the same purpose. The surface may be curved. An increased output may be obtained by secondary emission from the target 10, a collector electrode 90, Fig. 5, on the envelope or separate therefrom being biassed positively with respect to the target and collecting the secondary output and any stray electrons about the tube. The modulation is in one form applied to the wave supplied from a crystal oscillator 40, through the amplifiers 42, 44 to the primary 46 of an input transformer 56 ; the secondary 55 is connected to the pairs of deflecting plates 6, 8 within the cathode-ray tube, on one side to one of each pair directly and through the phase shifting circuit 58 to the other plates. By this arrangement oscillating potentials in quadrature are applied to the pairs of plates and the beam is caused to trace a circle on the target 10. A modulating potential is applied to the transformer AFT, which through the potentiometer PR, resistance 63 and condenser 65 is connected to the grid of a valve 68 ; the output circuit of this valve includes the condenser 69 which is connected to a radio frequency choke RFC in the anode circuit of the amplifier valve 44 feeding the transformer primary 46. Varying input on the transformer AT will thereby modulate the potentials applied to the deflector plates and cause a phase shift of the wave generated on the target 10. The output circuit from the cathode-ray tube includes ampliners 72, 76 and a frequency multiplier 74. Instead of modulating by varying the potentials of the deflecting plates, the modulating current may be applied to the accelerating electrode. If the output is to be frequency modulated the resistance 63 is of high impedance to the modulating frequencies received by AFT, and the condenser 64 of low impedance thereto. For phase modulations the elements 63, 64 are adjusted so that the modulating potentials from the valve 68 are independent of the frequency of the applied modulating potentials ; in this case the transformer AFT may be directly connected across the valve 68 without the elements 63, 64, 65, P.R. In addition to the modulation applied by the transformer AFT, an amplitude modulation is obtained by a transformer 100 connected to a grid in front of the cathode. Biassing potentials are supplied by a rectifier R.