GB389821A - Improvements in or relating to method of and means for transmitting electrical current waves over transmission lines of high attenuation - Google Patents

Abstract

389,821. Long-distance transmission. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.- (Assignees of Dudley, H. W. ; 123, South Oraton Parkway, East Orange, New Jersey, U.S.A.) Sept. 21, 1931, No. 26398. Convention date, Sept. 30, 1930. Drawings to Specification. '[Class 40 (iv).] To increase the ratio of speech level over cable noises in a submarine cable having high attenuation the terminating impedance is made either a pure reactance or of a value several times that of the impedance of the cable. The input to the cable is predistorted so that the upper portion of the frequency range is transmitted at the lowest transmission level permitted by interference from resistance noises, and the lowest portion of the frequency range is transmitted at the highest transmission level permitted by interference from modulation in the cable loading material. As the cable tends to attenuate the higher frequencies to a greater degree than the lower, the terminating transformer is given a low mutual inductance to give it a lower transmission efficiency for the low frequencies than for the higher frequencies. Condensers may be connected in series with the primary of the terminating transformer, either to form, with the mutual inductance of the transformer, a high pass filter primarily to keep out earth currents, or to assist in the equalization mentioned above by discriminating against low frequencies. Suitable balanced type terminating networks are indicated in the Specification for cables employing (i) earth return, (ii) twin conductors and (iii) concentric return systems. A mathematical investigation is included in the Specification which shows that for any cable a 3-decibel improvement over the matched impedance is obtained by making the terminating impedance either a substantially pure reactance or a resistance high in comparison with the cable resistance. Specifications 240,034, [Class 40 (iii), Telegraphs, Electric], and 339,685, [Class 40 (iv), Telephones &c.], are referred to.