ry, inter continental links for pro- sample rate reduction, differential coding (DPCM), transform cod- gramme exchanges. Short range microwave links may also be used ing, variable length coding and vector quantisation, or a combina- for portable radio cameras used in ENG (electronic news gathering), tion of these. The channel bandwidth of a digital signal depends on sportscasting etc., linking the camera with a mobile control room or both the bit rate and the modulation process. It should however be portable video recorder. noted that where digital video has been subjected to appreciable bit The original broadband video/sound links were concerned with rate reduction, or is in composite rather than component form, it analogue signals of black and white video; the later introduction of cannot be further processed or manipulated within the production analogue composite (encoded) waveforms for colour television process; the requirements of a contribution link may thus differ from that of distribution links. required significantly more stringent performance standards in order to minimise picture degradations resulting primarily from Direct to home digital broadcasting from terrestrial transmitters differential gain and differential phase. Over many years, radio would permit a very significant reduction of transmitter power and relay links have used frequency modulated carriers to convey anal- might permit the use of the SO called 'taboo channels' denied to ogue video waveforms, but from the 1970s onwards increasing use terrestrial broadcasters on account of co-channel and/or adjacent is being made of digital video, digital audio and digital data signals channel interference. Multipath leading to inter symbol distortion within parts of the programme chain with a corresponding gradual and consequent high bit error rates can be minimised by the use of introduction of digitally modulated carriers for terrestrial radio relay special modulation techniques such as Orthogonal Frequency Digi- and optical fibre links and also, 