GB1051663A - - Google Patents

Abstract

1,051,663. Pulse modulator. STANDARD TELEPHONES & CABLES Ltd. Feb. 20, 1964 [Feb. 27, 1963], No. 7899/63. Heading H3R. In an amplitude, frequency or phase modulator in which the carrier signal is modulated by a square wave pulse train, e.g. a telegraph signal, means are provided for adjusting the rise time of the modulated carrier wave pulses. In the frequency modulator shown in Fig. 1, the square wave signal is applied via terminals 3, 4 to a pulse shaper circuit comprising resistor 1 and capacitor 2 to provide a signal of the form shown in Fig. 2B. This signal is applied via an amplitude control 5 to the base of a transistor 9 which is adjustable biased by potentiometer 7 and the transistor output signal is applied to a second transistor 13 which includes a diode 19 in its emitter circuit. During positive excursions of the signal at the base of transistor 13 the diode is cut off and produces no effect on capacitor 23 which is one of the frequency determining components of carrier oscillator 25. During negative excursions the diode is driven to saturation and in consequence its low impedance effectively connects capacitor 21 in parallel with capacitor 23 and alters the carrier frequency. The rise time of the carrier signal pulsed is controlled by the amplitude of the signal applied to transistor 13 which is determined by the setting of potentiometer 5 and where the input signal has equal mark to space ratio the modulated signal is adjusted for a similar ratio by potentiometer 7. Fig. 3 (not shown) shows application of the invention to an amplitude modulator.