GB823506A - Improvements in or relating to wired broadcasting systems - Google Patents

Abstract

823,506. Distributing music &c. COMMUNICATIONS PATENTS Ltd. Feb. 4, 1958, No. 3618/58. Drawings to Specification. Class 40 (4). In a wired broadcasting system, particularly one for television signals, a plurality of signals are distributed, in respect of the same programme material, in different portions of the frequency spectrum so as to enable the use by subscribers of either special receivers specific to the system or normal broadcast receivers. In a first embodiment a television picture signal modulated on a carrier wave of about 4.9 Mc/s. is distributed over a coaxial cable to which the special receivers may be coupled in any of the usual ways. To enable the use of broadcast receivers also, the picture signal is also distributed on a carrier wave of 45 Mc/s. To this end, the cable is equipped at intervals with low-pass filters which prevent the passage of the 45 Mc/s. sideband(s), thus providing portions of the cable which are electrically isolated from one another for those frequencies. For each such portion a frequency converter and amplifier receives the modulated 4.9 Mc/s. carrier from the cable and supplies to that portion of the cable, preferably at its centre, a correspondingly picture-modulated carrier of 45 Mc/s. The sound signals are dealt with in a similar manner. In a second embodiment two two-wire lines are provided, over the first of which the picturemodulated 4.9 Mc/s. carrier is distributed and to which the special receivers are coupled. The second two-curve line is divided into electrically-isolated portions, as far as the modulated 45 Mc/s. carrier is concerned, by low-pass filters, each such portion being supplied with modulated 45 mc/s. carrier by a frequency converter and signal amplifier taking its input from the first two-wire line. The sound signals may be distributed on the first line as audio-frequency signals, a modulator being provided in association with each frequency converter and signal amplifier to provide to the second line a correspondingly modulated carrier wave of 41.5 Mc/s., corresponding to the sound channel frequency of a broadcast receiver tuned to the 45 Mc/s. picture carrier wave.