A linear phase modulator for large baseband bandwidths

A linear phase modulator with a stable carrier frequency would be a useful component in radio systems — especially in coherent phase-shift-keyed PCM systems with baud rates of the order of 100 megabauds per second. The Armstrong modulator appears adequate for these applications; the circuit functions required for its realization are well understood and amenable to the techniques of integrated circuitry. In this paper, an analysis of the signal and distortion properties of the Armstrong circuit and variations of it are presented and applied to three system applications: as a replacement modulator for existing low-index analog systems; for multilevel coherent phase-shift-keyed PCM systems; and for frequency-division frequency-modulation multiplex systems which are of interest in radio trunk systems.