GB1287480A - Carrier frequency generator - Google Patents

Abstract

1287480 Frequency synthesizers; multiplex systems SOC ITALIANA TELECOMUNICAZIONI SIEMENS SpA 8 Dec 1969 19 May 1969] 59837/69 Headings H3F and H4R [Also in Divisions G4-G6] A carrier frequency generator for use in a multi-channel communication system comprises division means for generating some of the required frequencies by frequency division of a fundamental higher frequency signal and means for generating the other required frequencies by by generating and selecting harmonics of one or more of the frequencies obtained by division the generating means comprising at least one coincidence circuit arranged to receive a plurality of signals at different frequencies generated by the division means and to generate pulse signals of short duration, the said other frequencies being selected from the harmonies of the output of the or each coincidence circuit, the higher frequency signal and the frequencies generated therefrom by division being square wave signals. The various output frequencies are obtained by means of bandpass filters from a generator of rectangular waveforms, comprising a crystal oscillator driving a squaring circuit (not shown) which feeds into a network of dividers. From the frequency 1440 KHz frequencies of 96 and 16 KHz are obtained by means of dividers 1 and 1, 2, 3 respectively, while frequencies of 120 and 20 KHz are obtained by means of dividers 4-6 and 4-8 respectively. An additional divider 9 gives the frequency 60 KHz and dividers 10-12 the frequency 12 KHz. In each case, the corresponding sine waves are obtained by means of bandpass filters. The outputs from dividers 10, 11, 12 are applied to an AND gate A, the output from which comprises a train of narrow pulses at 12 KHz repetition frequency. The outputs from dividers 4, 5 and from AND gate A are applied to AND gate B to obtain a further train of narrow pulses of 12 KHz repetition frequency. The outputs from AND gate B are a divider 15 are combined in AND gate 16 to derive a train of narrow pulses of 4 KHz repetition frequency, while the outputs from AND gate A and a divider 1 3 are combined in AND gate 14 to derive a train of narrow pulses at 6 KHz repetition frequency. In each case, desired output frequencies are obtained from the higher harmonics present in the narrow pulse trains, by means of bandpass filters.