GB595885A - Multichannel carrier transmission system - Google Patents

Abstract

595,885. Multiplex systems. CREED & CO., Ltd. July 20, 1945, No. 18642. Convention date, Sept. 6, 1944. [Class 40 (iv)] A multi-channel high-frequency carrier transmission system comprises means for grouping the individual channels into a plurality of basic groups, each group consisting of the same number of channels occupying the same section of the frequency band covered by the system at the lower end of the said band, means for translating upwards the frequency band of certain of the basic groups in order to form a plurality of unit groups, each unit group consisting of the same number of basic groups arranged respectively to occupy adjacent frequency bands, the same for all unit groups, means for repeating the process to form a plurality of larger unit groups, means for translating upwards the frequency band of at least one of the larger unit groups so that it occupies a frequency band adjacent to and above the band occupied by another larger unit group, and means for transmitting these larger unit groups over a single transmission path. As shown, Fig. 1, a 72 channel two-way telegraph system comprises eight basic groups a to h, each of nine channels, the frequencies of which range from 750 cps. to 3150 cps. with a 300 cycles channel separation. The basic groups b, d, f and h are each translated upwards by a modulator M1 using a 3.3 kc. carrier, the output of which passes to a band pass filter F 1 and is combined with that of a filter F comprising basic groups a, c, e, g respectively and four unit groups are formed of frequencies from 600 cps. to 6600 cps. The output of the filters F and F1 of the second and fourth unit groups respectively are translated upwards by modulators M2, using a 6.9 kc. carrier, filtered by band-pass filters F2 and combined with the first and third unit groups respectively to form two larger unit groups of frequencies from 600 cps. to 13,500 cps. The second of these larger unit groups, comprising basic groups e to h, is further translated by modulator M3, using a 15 kc. carrier, filtered by filter F3 and together with the other larger unit group is then translated by modulator M4, using a 34.5 kc. carrier, filtered by filters F4 and amplified before passing to the outgoing line L. Similar arrangements are made for reception at R<1>, Fig. 2. The arrangements for transmission from T<1>, Fig. 2, to R, Fig. 1, in the reverse direction are similar, differing only in the omission of the final modulator M4 and the substitution of filters F5 for F4.