Digital Terrestrial TV Broadcasting
The present plan for introducing digital terrestrial television (DTT) in the UK will result in DTT multiplexes being transmitted from 81 sites by the millennium. These transmissions will cover from 90% down to 60% of the population, dependent upon multiplex, compared with 99.4% for existing analogue services. It is desirable to cease analogue TV transmissions as soon as possible in order to make spectrum available for alternative uses and this change is likely to be more acceptable to the public if more DTT coverage can be achieved. Due to the significant differences in analogue and digital signals it has been possible to plan a network of digital transmissions which are interleaved with the analogue transmissions and this has been a major achievement in itself. However in order to extend DTT transmissions to more sites, the difficulty of doing so increases disproportionately due to the scarcity of available spectrum. Many of the first 81 sites have restrictions placed upon them such that radiated power in certain directions is severely limited in order to avoid interference with other broadcasts in the UK and mainland Europe.
Programme of work
A number of technical concepts which should significantly aid the achievement of these objectives have been identified by the LINK project consortium. Those that are identified as work packages that Oxford has responsibility for and will co-ordinate are:
- Application of new technologies to provide low phase noise, low noise figure and low amplitude ripple receivers, in order to permit the use of rebroadcast transposer techniques with minimal loss of decoding margin.
- Transpositions of one or two channels through the use of high stability and high performance UHF filters. This would facilitate the use of channels which would otherwise not be available for service planning.
- Low loss components to improve the linearity of power amplifiers.