GB516793A - Improvements in electromagnetic wave signalling systems - Google Patents

Abstract

516,793. Multiplex systems. TENNANT, W. J. (American Optical Co.). July 8, 1938, No. 20257. [Class 40 (iv)] [Also in Group XL] In a high-frequency broadcast system covering a large area, and suitable for television, the signal-modulated carrier-wave is fed from a central station over a system of branched non- radiating transmission lines 2 and 4 through coupling impedances 3 and booster stations 6, 10 to a number of radiators 6, which are spaced to cover the broadcast area with little overlap, thus minimizing distortion due to interference. The booster stations may be automatically ,controlled from the central station by low-frequency or direct current impulse signals sent out over the transmission lines. The coupling impedances 3 serve to prevent reflection which would affect the electrical length of the transmission lines. The aerials are preferably directional and may comprise doublets with their axes at right-angles in order to minimize overlap. Other radio programmes, either sound or television, of different carrier-frequency, may be broadcast simultaneously and the programmes may also be transmitted directly over a line 8 to a receiver 9. A number of telephonic and telegraphic signals can also be transmitted over the line system on a carrier of different frequency which is modulated by sub-carriers of intermediate frequency, each of these being modulated by a signal. Reference has been directed by the Comptroller to Specification 440,143 and U.S.A. Specification 2,033,271.