GB426855A - Modulation system for high frequency wireless transmission - Google Patents

Abstract

426,855. Valve modulating circuits. HAZELTINE CORPORATION, 15, Exchange Place, Jersey City, New Jersey, U.S.A.- (Assignees of Wheeler, H. A.; 18, Melbourne Road, Great Neck, New York, U.S.A.) July 11, 1934, No. 20377. Convention date, July 12, 1933. [Class 40 (v)] A thermionic modulation system comprises a valve having two grids separated by a positively biassed screen electrode, modulating potentials being applied to one grid and radiofrequency oscillations to the other, the output circuit being between anode and cathode. The Figure shows a hexode valve in which a virtual cathode is formed between the positively biassed inner screen 3 and the negatively biassed outer control grid 4 to which modulating potentials from the microphone 19 are applied. In this case radio frequency oscillations are applied to the inner control grid 2 by back coupling the screen grid 3 to the inner grid circuit at 16, 15, 18. Improved working is obtained by the use of a positively biassed second screen electrode 5. The modulating and radio frequency potentials may be transposed, the radio frequency being applied to the outer grid and the speech frequencies to the inner. The valve may be used as a plain modulator by dispensing with the back coupling and applying radio-frequency oscillations to the control grid, Fig. 3, (not shown). The modulating control grid is given a linear relation between grid voltage and mutual conductance to give distortionless modulation ; similarly the relation between grid voltage of the radio-frequency grid and space current is made linear to give distortionless amplification.