GB466418A - Improvements in or relating to electric signal transmission systems - Google Patents

Abstract

466,418. Transmission systems. BLUMLEIN, A. D. Nov. 22, 1935, No. 32471. [Class 40 (iv)] [Also in Group XXXVI] A concentric cable for transmitting a wide range of frequencies is provided with an additional conductor which in conjunction with the central conductor forms a balanced circuit for the lower frequencies for which the outer conductor is less effective as a screen against inductive interference. The additional conductor 4 with a paper covering 5 lies within a helical groove in the paper sheath 3 surrounding the central conductor 2. The latter is deformed in the manner described in Specifications 452,713 and 452,772, [both in Group XXXVI]. and the conductor 4 is arranged to have substantially the same length. The outer conductor comprises a thin layer of copper foil 6 overlaid with lead sheathing 7. Alternatively the additional conductor may lie within a lead sheath outside the lead sheath 7, both sheaths being contained in a common outer sheath. The additional conductor may also lie in a straight groove in the paper sheath 3, the lead sheath 7 being egg-shaped in cross-section, and four such cables may be combined to form a multiple cable in which the positions of the additional and central conductors may be rotated. The additional conductor may also consist of two or more separate conductors wound on the paper sheath 3. Circuits. In order to minimize interference the attenuation and velocity of propagation of the two circuits comprised respectively by the central and outer conductors and by the central and additional conductors should be approximately equal at low frequencies. The central conductor 2 is loaded at intervals with condensers 9 shunted by resistances 10 in the manner described in Specification 455,492, and also with condensers 11 to correct for the low-frequency effect referred to in the latter Specification. Condensers 12 in the additional conductor 4 maintain the ratio of the capacities between each conductor and the sheath. The line is terminated by condensers 13, 14 and a resistance 15 in series, and is coupled to a receiving valve 17 through a transformer 16. An additional valve may be used if necessary to receive the higher frequencies through a capacity coupling. At the transmitting end the central and additional conductors are separately earthed through a condenser and resistance in series. The central conductor 2 is fed through a condenser 20 by a valve 21 having a high resistance 22 between the anode and a source of high tension current. The input may alternatively be applied to both conductors 2, 4 by means of two valves in pushpull relationship. Since the high frequencies are propagated mainly through the central conductor it is. advantageous to connect a shunt condenser between the additional and the sheath at each end of the cable.