GB615207A - Modulating system for radio and like signalling - Google Patents

Abstract

615,207. Modulating systems. TRIGGS, \V. W. (Farnvorth Television & Radio Corporation). Feb. 6, 1945, No. 3017. [Class 40 (v)] In a modulation system modulation is performed in a frequency-doubling stage in such a manner that the output includes an inversely modulated component at the fundamental radio frequency, which is used after detection to produce additional modulation. The grids of the twin-triode modulator stage 11 are excited in push-pull from a radio frequency source over the centre-tapped tuned transformer 12. Modulating signals are applied to one triode which is biassed so that in the absence of modulation conduction occurs only in the other valve. An output at fundamental frequency is then produced and appears in the tuned circuit 28. Modulating signals cause conduction to occur in both valves, producing in the circuit 19 an output of second harmonic frequency proportional in amplitude to the modulating signal. The corresponding reduction in output at the fundamental frequency results in inverse modulation of the signal in the circuit 28. After demodulation by a double-diode 34, the inverse modulation appears across a resistance 26 to produce additional anode modulation of the modulator 11. In an alternative arrangement (Fig. 4, not shown), the detector output is applied in the form of grid modulation.