| 摘要 |
A wired broadcasting system comprises a plurality of subscriber stations each connected to a central exchange by a respective transmission cable, a plurality of bus-bars located at the central exchange, a plurality of program sources for applying television signals at a first frequency to respective bus-bars, a plurality of switches located at the central exchange for selectively connecting each subscriber cable to any one of the bus-bars, and at least one receiver at each subscriber station for receiving signals at the first frequency, each subscriber station being provided with controls for the switches, and at least two subscriber stations being provided with a generator of television signals at a second frequency and apparatus for applying the generated signals to the cables. At least one pair of the bus-bars are interconnected by a two-way frequency changer adapted to convert signals at the second frequency on either bus-bar of the pair to signals at said first frequency and to apply the converted signals to the other bus-bar of the pair. This enables two-way visual communication to be established between the two subscriber stations via the frequency changer. |
