Improvements in or relating to frequency modulation oscillation generators

摘要

652,896. Frequency modulation. STANDARD TELEPHONES & CABLES, Ltd. May 28, 1948, No. 14449. Convention date, June 2, 1947. [Class 40 (v)] A frequency modulated oscillation generator comprises a pair of grid-controlled valves 10, 11 and a tuned oscillatory circuit 30, 31 connected in like phase to the valve anodes 24, 25 wherein voltages of mutually different phases are fed back from the anode circuit to the valve grids 14, 15 and signal voltages are fed to valve grids 20, 21 for correspondingly and oppositely varying the respective mutual conductance of the valves so as to vary the frequency of oscillation. The grids 14, 15 are negatively biassed so that in the absence of signal voltages the oscillator generates a predetermined frequency, the voltage fed back to grid 14 passing through a phase-shifting network 37 producing a voltage on the grid leading that at a point B in the anode circuit by about 30 degrees, whilst the voltage fed back to grid 15 passes through a network 38 producing a voltage on the grid lagging that at the point B by about 30 degrees. The signal voltages applied to grids 20, 21 serve to vary the bias on one valve an equal and opposite amount to that at the other so that the mutual inductance of the valves are correspondingly altered, carrying the frequency of oscillation to shift from the predetermined value.