GB369112A - Improvements in or relating to modulating systems for electric oscillations - Google Patents

Abstract

369,112. Wireless transmitting systems. MARCONI'S WIRELESS TELEGRAPH CO., Marconi House, Strand, London.-(Assignees of Roberts, W. van B. ; 155, Hodge Road, Princeton, New Jersey, U.S.A.) July 10, 1931, No. 19902. Convention date, July 10, 1930. [Class 40 (v).] Frequency modulation is effected by varying a resistance associated with a capacity, the capacity-resistance combination being connected to or coupled with the frequency control circuit of the carrier source. The capacity is the apparent input capacity of a thermionic valve, and the resistance is in its plate circuit and may comprise the plate-filament path of a second valve. This arrangement is shown in Fig. 3, in which the tuned circuit 16 of a valve generator 28 is connected across the grid and cathode of a valve 2, so that the input capacity of this valve is in parallel with the tuned circuit 16. The effective value of this capacity is varied by varying the external plate resistance of the valve 2. This resistance may comprise the modulating microphone, but as shown it comprises the plate-filament path of the valve 30, and the grid 32 of this valve is coupled to the microphone circuit 34, or to the circuit of a modulating source 38 and key 36. The signal produces variations in the frequency of the wave generated by the valve 28, which wave may be amplified at 40 and transferred to an aerial 41. The plate-grid capacity of the valve 2 may be supplemented by a condenser 39.