Patent GB-416396-A (GB)
Title: Improvements in or relating to modulated carrier wave transmitters
IPC: H03C3/04
Filed: 1933-07-24
Abstract: 416,396. Wireless transmitting systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.-(Assignees of Usselman, G. L. ; Port Jefferson, Long Island, New York, U.S.A.) July 24, 1933, No. 20866. Convention date, July 23, 1932. [Class 40 (v).] Phase-modulation and amplitude-modulation circuits are used jointly either for the purpose of multiplex communication, or for balancing out whichever form of modulation is undesired. The carrier-wave oscillator o, Fig. 1, is coupled to a resonant circuit 4, earthed at its mid-point through a condenser J1, and connected at one end through a phase-retarding coil E and phaseadvancing condenser F to the respective grids of valves V1, V2. The plates of these valves are connected to one side of a tuned output circuit 24 which is supplied with plate current at its mid-point. The modulating-source 14 is connected in push-pull relation to the grids of the valves V1, V2 through resistances R1, R2, and adjustable bias is applied to the grids from a potentiometer P. A phase-modulated wave produced in the output circuit 24 substantially in the manner described in Specifications 411,638 and 411,643 is transmitted to the aerial through amplifiers, frequency-multipliers, or limiters 30. An audio-frequency source 141 which may be the same as, or separate from, the source 14, is coupled by a transformer T2 to the grid circuit of a valve V3, which also has its grid connected through a variable resistance G and blocking condenser I to the side of the tuned circuit 4 opposite to that connected to the grids of valves V1, V2. The plate of the valve V3 is connected to the lower end of the tuned output circuit 24 and supplies thereto an amplitude-modulated wave the strength of which may be varied by adjusting the resistance G or the grid-bias potentiometer P. Separate signals may be sent by phase-modulation and amplitude-modulation respectively. The amplitude modulator may be rendered inoperative by throwing the switch K, and the depth of phase modulation may then be varied by adjusting the bias potentiometer P for the valve V3. When phase-modulation is used alone, the amplitude-modulation circuit may be adjusted to neutralize any accidental amplitude-modulation introduced by the phasemodulator ; and conversely if amplitudemodulation alone is to be transmitted, any accidental phase modulation may be balanced out. The second modulator may also be used to suppress hum. The tuned circuits 4, 24 may be cross-connected by neutralizing-condensers N1, N2 ; or screen-grid valves may be employed. In a modification, Fig. 2, a single audiofrequency source 14 supplies the phase-modulation system as in Fig. 1, and supplies the amplitude-modulator 40 through a phase-adjusting device 44 so that a more correct balancing out of accidental amplitude modulation may be effected in the amplifiers 41, 43. Balancing is also facilitated by a potentiometer P1 and reversing-switch S between the source 14 and the transformer Tl. The phasing-device 44 may also be interposed between the source 14 and the transformer T1, (Fig. 3 not shown). Specification 383,412 also is referred to. The Specification as open to inspection, under Sect. 91 refers to an arrangement in which two audio-frequency sources of different frequency are used to phase-modulate the carrier, one source being connected to a pair of valves as in Fig. 1, and the other source to a second pair of valves associated with the opposite sides of the tuned circuits 4, 24. This subject-matter does not appear in the Specification as accepted.