GB388066A - Improvements in or relating to radio and other high frequency circuit arrangements - Google Patents

Abstract

388,066. Wireless transmitting systems ; valve modulating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London, LUNNON, F. C., Westdene, Roxwell Road, and WASSELL, H. J. H., 77, Mildmay Road, Chelmsford, both in Essex. Aug. 18, 1931, No. 23282. Addition to 351,051. [Class 40 (v).] Radio and like valve transmitters are arranged as in the parent Specification so that one or more valves which act as amplifiers during signalling periods have their circuits changed so that they function to maintain a load on the H.T. supply during non-signalling periods ; and the present invention comprises (1) an adaptation of this system to radio telephony and (2) a modified circuit for radio telegraphy. Fig. 1 (Prov.) shows part of the telephony circuit, the remainder being the same as in Specification 351,051. The last amplifying- valve V3 includes in its grid circuit an inductance coil Z1, a modulating-valve MV shunted by a diode valve GL, and a portion P3 of a potentiometer resistance Z. Other tappings P0, P2 connect the grid circuits of earlier valves in the amplifying chain. The resistance Z is in circuit with a battery B1 and a valve K1, the grid of which is energized by rectified speech voltages obtained from the microphone M through an amplifier-rectifier ATD. The microphone is also connected through a transformer MT to the grid of the modulator MV. When speech is being transmitted, the valve K1 is blocked, and the potentiometer inoperative. At a predetermined period after the cessation of speech, the valve K1 becomes conductive, and the tappings P0, P2, P3 function as in the parent Specification to suppress the carrier wave, whilst leaving the valve V3 and possibly earlier valves in the chain, as a load on the H.T. supply. The diode valve GL, which as shown comprises a triode valve with a connection between grid and plate, enables the negative potential at P3 to reach the grid of the valve V3. Fig. 1 (Comp.) shows the modified circuit arranged for telegraphy. The signal key or like interrupter M1 which is opened for signals, and closed for spaces, is shunted by a source B11 and a resistance R, and is connected across the grid and filament of a valve K1, the plate circuit of which includes a source B1 and the potentiometer Z. The tappings P0, P2, P3 are connected to the grids of the transmitter valves, the connection of tapping P3 including a high resistance L. If desired the valves MV, GL, Fig. 1 (Prov.), may be retained instead of the resistance L, and the grid of the-valve MV suitably biased.