GB982312A - Improvements in or relating to information transfer systems and linear pulse frequency modulators therefore - Google Patents

Abstract

982,312. Pulse modulation systems. M. E. AYNES. May 15, 1961, No. 17645/61. Heading H4L. A signal of varying amplitude is converted into a pulse train whose repetition rate varies as the amplitude of the signal, pulse shapers providing pulses of constant amplitude and duration being provided at both the modulating and demodulating stages so that any distortion arising during transmission is minimized. In one arrangement two independent signals are modulated, mixed, recorded, and subsequently separated and demodulated. Signals from sources 310, 310<SP>1</SP>, Fig. 3, are pulse modulated by modulators 312, 312<SP>1</SP> which by means of transistor multivibrator circuits produce pulses of constant duration, the duration differing for each channel, and separated by " off " states which decrease with increase of the applied signal potential at the base of the first transistor. The pulses are then shaped to a standard amplitude and duration particular to each channel by pulse shapers 314, 314<SP>1</SP>. The pulse trains of each signal are taken therefrom in opposite phase, the differing amplitude and duration for each channel avoiding mutual cancellation. The separate signals A, B, Fig. 5, are combined to produce a waveform at the input terminals of a magnetic tape recorder 318. During this recording operation, branch signals are passed through demodulation filters 316, 316<SP>1</SP> for monitoring purposes. During playback, signals are taken from the recorder separated into the two channels by oppositely poled rectifiers 317, 317<SP>1</SP>, and passed through amplifiers 319, 319<SP>1</SP> and pulse shapers 314, 314<SP>1</SP> to demodulation filters 316, 316<SP>1</SP> which integrate the pulses into voltages corresponding to the original signals which are applied to utilization devices. In an alternative arrangement, Fig. 2 (not shown), the system is described as a diplex communication link, the tape recorder being omitted. A single channel arrangement is described, Fig. 1 (not shown), in which the pulse shaper may be switched to alter its characteristics to suit different playback speeds.