GB822769A - Improvements in or relating to picture transmission systems - Google Patents

Abstract

822,769. Television intercommunication networks. DECCA RECORD CO. Ltd. May 20, 1958 [June 7, 1957], No. 18154/57. Class 40 (4). [Also in Group XL (b)] A plurality of television stations, each of which is arranged for both transmission and reception with the aid of a single cathode-ray tube (see Group XL (b)), is connected by a coaxial cable network so as to permit intercommunication. Fig. 8 illustrates a network for six stations 110 to 115. Each station has a video input terminal 27, a video output terminal 35 and a synchronizing signal input terminal 20. A further terminal 30 is strapped internally to terminal 20. A common synchronizing source 116 supplies all the stations, cables being, taken from terminal 30 of one station to terminal 20 of the next and so on. A cable extends from the video output of each station to all the other stations and selector boxes 120 to 125, each with five switches, are associated one with each station -to enable desired connections to be set up between stations. The network provides the following facilities: (1) any station may transmit to one or more other stations and any: station may receive from one or more other stations, (2) the stations may work together in pairs or groups simultaneously, each pair or group being independent of the others, and (3) a station may relay picture information received from one station to another, if desired with further picture information added locally. The facility whereby one station may receive information from two or more stations is stated to be of value where information is to be combined in tabular form, each station being allocated a different part of the image area. To permit signals from two sources to be combined at a receiver without interaction, isolating resistors (as shown) or cathode followers are included in each lead from the selector boxes. Audio channels (not shown) are also provided between stations. In a second generally similar embodiment, Fig. 7 (not shown), means are provided whereby the synchronizing signals are combined with the video signals at each transmitting station and sent over a common channel. Each receiver then includes a conventional synchronizing signal separator in the video input channel and is synchronized directly from the transmitting station with which it works. This arrangement prevents image displacement due to differing delays in the synchronizing signal distribution cables between transmitter and receiver. Other embodiments, Figs. 4 to 6 (not shown), comprise networks arranged for two and three stations.