EBU Technical Review : No. 261 (Autumn 1994)
Digital Audio Broadcasting (or DAB) is arguably the most important technical development in sound radio broadcasting for very many years. Of course, this is said about most new developments, usually before their introduction and occasionally before any testing has taken place. This time it seems likely that the use of the superlative ("most important") is well justified. DAB looks set to offer the listener higher quality radio reception than has been possible before and will offer that quality even in the hostile receiving environment encountered by portable and mobile equipment.
It is well known that portable and mobile reception can be difficult but it is worth noting why this is so, especially in urban areas. Radio waves are subject to attenuation by obstacles, natural or man-made, and in addition are reflected from them. The environment of an urban area is thus an almost ideal hostile one for radio waves. Reception at a few metres above ground level will be disturbed by the attenuation of the radio signals by the buildings and also by the reflections, and even multiple reflections, from and between buildings. With FM reception, the results are the well-known ones of signal loss and distortion – even though broadcasters go to considerable lengths to choose their transmitter sites and radiated powers to minimise the difficulties for the listeners.
Inside buildings there are also potential reception problems because in addition to the difficulties noted above for outdoor reception, there is signal attenuation by the walls and additional reflections from objects inside houses. In view of all of these potential problems, it is perhaps surprising that portable and mobile reception on FM is possible at all.
DAB, which in the context of this issue of the EBU Technical Review means the Eureka 147 system, has the potential to overcome all of these problems. It has the ability to take advantage of the energy in the reflected signals and to use it to enhance reception. It has been designed to be robust and not only to survive in a hostile environment but to thrive there.
However, to be designed is one thing, to perform may be another and the design aims must be well tested before any new broadcasting system (which is intended as a replacement for an existing system) can be put into operation. This issue of the Review concentrates on the matter of field tests for DAB. Such tests are intended to demonstrate the effectiveness of a system in the real receiving environment, to find its strengths and, if possible, its weaknesses. The latter point is an important one. If there are any weaknesses, they must be found in advance so that their effects can be taken into account and minimised during the introduction of a new service.
The tests reported in this issue of the EBU Technical Review are not the only ones which will be made. It is expected that other tests, probably in other frequency bands and other receiving environments, will be reported in forthcoming issues. They can be seen as scientific examination of a new system and also as herald of a new era of radio broadcasting.
European Broadcasting Union
