to some degree, for satellite links in tal Modulation (OFDM) of a large number of spaced carriers. accordance with ISDN hierarchial levels. Video signals conveyed over relatively short distances of coaxial cable in studio routeing systems are normally transmitted directly at Television transmission video frequency. When the cable path exceeds about 100m the distribution amplifiers may provide passive equalisation to offset 57.2.1 Fundamentals and standards the distortions caused by the attenuation and delay characteristics of the cable. For cable systems extending beyond about 500m, the All television systems are based on translating a scene into a series video signal modulates a carrier frequency between about 20MHz of small points, termed picture elements (pixels), by methodically to 70MHz, using either double sideband or vestigial sideband am- tracing out or scanning the picture, and then conveying the intensity plitude modulation, suitable for distances up to a few km without (light value) of each picture element in an agreed sequence. At the intermediate amplifiers. receiver, a reproduction of the image is built up by means of an A re-broadcasting link (RBL) is a commonly used method of identical and synchronised scanning sequence (Figure 57.1). The feeding programme information from a main transmitter to its low display screen glows with an intensity dependent upon the light power gap filling relay transmitters. The key component of an RBL value of the pixels, with a degree of integration (memory) in both is a high grade re-broadcasting receiver (RBR). RBLs may also be camera and display. This, combined with the persistence of vision used to link high power main transmitters forming a regional net- of the eye, gives the viewer the impression that the display is work. Incoming signals presented to the RBR are usually not de- presenting a complete series of pictures with a resolution depending modulated at gap filling relays but converted to an intermediate on the total number of pixels in each frame; if subs