GB880160A - Improvements in or relating to electrical signal transmission systems - Google Patents

Abstract

880,160. Multiplex transmission systems. TELEPHONE MANUFACTURING CO. Ltd. April 6, 1960 [April 22, 1959], No. 13700/59. Class 40 (4). In a multichannel electric signal transmission system including at least two double sideband sources of which the upper sideband of one is contiguous with the lower sideband of the other, a band stop filter is used to suppress the contiguous sidebands. By using a band-pass filter in conjunction with two similar double sideband sources and adding the outputs of the two filters a range of at least four contiguous single sideband channels is obtained. In Fig. 1, two carriers of frequencies #c 1 and #c 2 (#c 2 >#c 1 ) are modulated by signals #m 1 and #m 2 , the contiguous sidebands #c 1 + #m 1 , #c 2 - #m 2 being suppressed by band-stop filter BSF. Fig. 2 shows the same two carriers modulated by signals #m 3 , #m 4 respectively, and in this case the non- contiguous sidebands fc 1 - fm 3 , #c 2 + #m 4 are suppressed by band-pass filter BPF. If the filter outputs of Figs. 1 and 2 are combined we obtain a two carrier system using the four sidebands as independent channels. A sixchannel system needing only three carriers (Fig. 3), uses band-stop filters to suppress the contiguous sidebands obtained by modulating carriers #c 1 , #c 2 and #c 2 , #c 3 with the four signals #m 1 , #m 2 and #m 5 , #m 6 respectively, and uses a band-pass filter to suppress the non-contiguous sidebands obtained by modulating carriers #c 1 and #c 3 with signals #m 3 and #m 4 respectively.