GB711762A - Coders for electric pulse code communication systems - Google Patents

Abstract

711,762. Pulse code modulation circuits. STANDARD TELEPHONES & CABLES, Ltd. Oct. 31, 1952 [Jan. 2, 1952], No. 27439/52. Class 40 (5) Binary pulse code groups are derived from a frequency-modulated carrier, by sampling the latter, feeding the samples to a plurality of mixers, one for each code digit, supplying the mixers also with the outputs of preselected ones of a plurality of heterodyne oscillators, and thus producing the appropriate code digit outputs, which are converted to code pulses corresponding to the sample frequency. In the embodiment described, sample signal amplitudes derived from an audio source 3, Fig. 1, in circuits 4, 7, 8 frequency modulate an oscillator 11, the output from which is converted to an intermediate frequency in mixer 13 fed from the oscillator 12, the frequency-modulated I.F. samples being applied to the five-digit coding circuit 2. The latter comprises a circuit 15, shown in more detail in Fig. 4, which produces simultaneous A.C. pulses at the inputs of those of the five digit circuits 20, 22 which represent the sample frequency on the code employed. Circuits 20 are provided to produce standard length A.C. pulses which are rectified in circuits 22 and distributed in time by the delay line 23. The pulses of the resulting code group, which groups are in the cyclic progression code, are regenerated to a constant amplitude by a single-stability trigger circuit 24 and may be converted to groups in the simple addition code, in known manner, by a double-stability multivibrator 25. The coder circuit 15 receives the frequency-modulated samples over conductor 28, Fig. 4, which forms one of the inputs of each of five mixer circuits 37 ... 41. In one example, the sample frequencies vary from 16 to 32 Mc/s and the mixer output circuits are shunted by resonant circuits 42 ... 46 respectively, tuned to 70, 71, 73, 77 and 81 Mc/s respectively and having bandwidths Π1/2, Π1, Π2, Π4 and + 4 Mc/s respectively. The other mixer inputs are selected from the outputs of eights oscillators 29 ... 36, generating waves of 53, 45, 49, 41, 51, 47, 43 and 39 Mc/s respectively. The first and second digit mixers 41, 40 receive the output from oscillator 29, the third 39 from oscillators 29, 30, the fourth from oscillators 29 ... 32 and the fifth from all the oscillators. In the case, for example of an input sample pulse of 24.7 Mc/s, this frequency combines in mixers 41 and 40 with the 53 Mc/s of oscillator 29 producing an upper sideband frequency of 77.7 Mc/s which is passed by circuits 46, 45 corresponding to digits 1 and 2. It also produces an upper sideband frequency of 69.7 Mc/s in mixer 37 with the 45 Mc/s of oscillator 30, which is passed by circuit 42 of digit 5. No sidebands produced bv mixers 38, 39 pass the circuits 44, 43 corresponding to digits 3 and 4.