GB243683A - Improvements in high frequency signalling systems - Google Patents

Abstract

243,683. British Thomson-Houston Co.. Ltd., (Assignees of Carter, E. F.). Nov. 25, 1924, [Convention date.]. Thermionic amplifiers, generators, and modulating systems; combined transmitting and receiving arrangements; coupling aerial and detector circuits; wired wireless systems.-In a combined transmitting and receiving set the oscillations of the transmitter are inhibited, when not required, by a high impedance inserted in the high tension supply to the oscillator, this impedance comprising a valve with negative grid. In the oscillator 2 the filament is connected through a resistance a to the grid and plate, the plate being in series with a rejector circuit b one point c of which is connected to the filament. High tension is supplied to the plate over a circuit comprising the filament, the choke d (which prevents the control valve from modulating the output of the oscillator 2), the plate-filament path of the control valve 7, the high-tension commutator @ of the generator 8, and the choke f. Normally this high-tension supply circuit is interrupted owing to the negative grid bias of the valve 7, which is provided by the battery 9 : but when voice currents from the microphone 6, amplified by the valve 5, act on the grid G7 through the transformer secondary 10, the impedance of the valve 7 is lowered and the valve 2 is consequently enabled to oscillate. The plate of the latter valve is connected through the condenser 12 and resistance g to the grid of the power amplifier 3 whose plate is choke coupled to the modulator 4. The output coil 13 is coupled to the tuned link circuit 14 and so through condensers 15 to the power line or other antenna 1. The receiver 16, tuned to the same frequency as the transmitter, is connected to the link circuit 14 by a further link circuit 18, but the latter is bridged by a diode 20 whose plate is somewhat negative with respect to its filament. This diode shunts the strong transmitter signals. but has no effect on the weak received signals.