GB440241A - Improvements in or relating to multi-channel electric signalling systems - Google Patents

Abstract

440,241. Multiplex signalling. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Chesnut, R. W. ; 115, Inwood Avenue, Crane, R. E.; 446, Valley Road, both in Upper Montclair, New Jersey, and Huber, G. H.; 332, East 7th Street, Brooklyn, New York, both in U.S.A.) May 24, 1935, No. 15225. Con. vention date, May 26, 1934. Drawings to Specification. [Class 40 (iv)] In a single line multi-channel signalling system wherein the different channels consist of different frequency bands, the signals are transmitted over the various channels at energy levels dependent on the attenuations of the respective channels and on the level of the combined interference due to noise inherent in the respective channels and to the presence of signal currents in other channels. The noise inherent in a channel includes all interference not due to operation of the line itself such as static, resistance noise, cross talk from other lines and induction from power lines. The interference due to signals in other channels on the same line comprises modulation products consisting of harmonics and combinations of frequencies due to non- linear characteristics of the lines and associated equipment. The invention enables more or higher grade channels to be obtained from a given line or the same number and grade to be obtained from a cheaper line of higher attenuation. The Specification contains a mathematical discussion of the problem and shows how to calculate the transmitting levels assuming specified margins for signal level over combined interference level and for modulation products below the natural noise level. In a two-way multi-channel system using different bands for the two directions, the modulation products in a channel due to other channels in the same direction and to the corresponding opposite bound channel may be neglected. Different combinations of opposite bound channels should also be considered since although interaction between opposite bound channels of a pair is not important, interaction between different pairs may vary for different combinations.