GB556208A - Arrangement for conversion of frequency modulation to phase modulation and the application thereof to the production of a frequency modulated wave from a frequency stable oscillator - Google Patents

Abstract

556,208. Frequency and phase modulation. STANDARD TELEPHONES & CABLES, Ltd., and EARP, C. W. April 25, 1941, No. 5358. [Class 40 (v)] Converting phase modulation to frequency modulation. A loop circuit comprises two modulators M3, M4, Fig. 2, and two tuned filters X3, X4 with or without a delay network D2. The filters are tuned respectively f and F Πf. A stable frequency source O applies the frequency F directly to the modulator M4, and through a phase modulator PM to the modulator M3. The filters and/or the delay network are arranged to give a phase shift proportional to frequency deviation, and the loop generates oscillations of mean frequencies f and F tf with a frequency deviation proportional to the phase shift in the modulator PM. The loop may be caused to oscillate initially by switching in a source OS. The phase modulator PM may be of the kind described in Specification 534,955 and as shown in Fig. 1. In this diagram a frequency-modulated wave from A of mean frequency f is combined in a modulator M1 with waves of stable frequency F from a source O. The sum (or difference), frequency is selected by a filter X1 and passed through a delay network D1 to a modulator M2 where it is combined with the original frequencymodulated wave from A. The resulting difference (or sum) frequency is selected by a filter X2, and consists of a phase-modulated wave of the stable frequency F. The filter X1 and/or the network D1 are designed to give a phase shift proportional to frequency.