GB1411260A - Device for controlling the frequency of a frequency modulated telegraphic transmitter - Google Patents

Abstract

1411260 Digital transmission: frequency keying ADRET-ELECTRONIQUE 22 Dec 1972 [4 Jan 1972] 59301/72 Headings H3A and H4P A frequency-shift keying generator uses the two-level input control signal at 20, 21 to change by way of a coding matrix 5 the ratio of a frequency divider 2 in the phase-lock loop controlling an oscillator 1. The output of the divider 2 is compared in a phase comparator 3 with a standard frequency from 12. The two frequencies thereby selectively obtained from the oscillator 1 are divided at 4a and used to control a frequency synthesizer 4b whose output is then a carrier frequency of between 2 and 32 MHz, for example, with a keying modulation shift of 100 Hz or a multiple thereof. By using a second control signal and a second control circuit 6-21 (not shown), and modifying the coding matrix 5, the divider may adopt four different ratios to give four-frequency keying. The control circuit employs a light-link 19 supplying the control signal to NAND gates 8, 9, which also receive the standard frequency 12. A bi-stable 6, 7 is thereby set and reset by the control signal only when a positive-going edge occurs in the sample frequency 12, and provides sufficient delay for the counter 2 to respond to the numerical output of the coding matrix 5 before the latter is changed by the bi-stable in response to a near control signal. A potential divider 13, 14, and equal frequency dividers 15, 16, provide ways of modifying the frequency switching time of the oscillator 1.