| 摘要 |
<p>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 programms 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 said first frequency, each subscriber station being provided with means for controlling said switches, and at least two subscriber stations being provided with means for generating television signals at a second frequency and for applying the generated signals to said cables. At least one pair of the bus-bars are interconnected by a two-way frequency changer adapted to convert signals at said second frequency on either bus-bar of said pair to signals at said first frequency and to apply the converted signals to the other bus-bar of said pair. This enables two-way visual communication be established between the said at least two subscriber stations via said frequency changer.</p> |
