GB1287995A - - Google Patents

Abstract

1287995 Pulse modulation; frequency modulation MOTOROLA Inc 24 Feb 1970 [10 March 1969] 8724/70 Headings H3R and H4L In a phase modulation circuit ramp signals are generated at 14 in response to R/F pulses from an oscillator 13 and compared at 15 with an audio signal from microphone 10 to produce width modulated pulses (a) Fig. 2, in known manner in which the leading edge varies in accordance with the modulating signal. These pulses are supplied via circuits 16, 18, which emphasize, Fig. 2(b), and attenuate Fig. 2(c), the high frequency components of the respective inputs of a comparator 20 which is provided with D.C. bias from 19 to establish the point at which the comparator changes state. The output of the comparator 20, Fig. 2(d) consists of narrow position modulated pulses which are supplied via a filter 21 to a frequency multiplier 22 to produce a phase modulated carrier wave. To increase the amount of phase shift the output of comparator 20 may be converted into a position modulated ramp signal which is coupled to a further comparator together with the audio signal. The output of this further comparator is then coupled through preemphasis and de-emphasis circuits to a final comparator and filtered and frequency multiplied as before.