This paper is intended to set the scene for the presentations that will follow. It looks at the characteristics of the direct broadcast TV services that were agreed internationally at the 1977 World Administrative Radio Conference (WARC) and at the effects of these characteristics on the communications link and thus on the spacecraft that will provide the services.

We are at the beginning of a decade of extraordinary change in telecommunications. Computers and information are joining together in a way which demands new techniques and capability in the field. Evolving demand and attitudes towards television, epitomised by the attention being given to direct broadcasting, are influencing national policy to many countries.

Today it is possible to ‘hook up’ video games and video recording equipment to the domestic television set. Data services are available to the viewer and small home computers can be connected. Direct-to-homes TV broadcasting is an addition to these facilities, extending the range of what is becoming a complete home entertainment and information service.

This paper discusses some of the factors that need to be taken into consideration if other services are to be included within a satellite that provides direct TV broadcasting to the UK. The main reason for considering such an approach is that the inclusion of other services may improve the overall economics.

It should be recognised that the requirements of the DBS services will impose certain constraints, in particular on the orbit location. Also there is less flexibility in the choice of frequencies for the DBS services than there may be for other services.

The first major step in the L-SAT programme was the publication by ESA in 1979 of the report ESA/EXEC (79) 3, (known as the ‘Blue Book’) which identified the market potential for a ‘large’ communication spacecraft and many of the essential features required to service the market needs. One of these features was the desirability for a multi-purpose platform which is now the basis of the overall L-SAT programme and the prime objective of the L-SAT 1 mission.

Great interest is being generated in direct broadcasting from space. In the future, several satellites will give individual users who are suitably equipped the option to select from over 40 programme channels. This paper is intended to outline the general system characteristics and requirements and considers the practicalities of siting and setting up a small receive-only terminal. Possible impairments resulting in signal degradation are described.

Let us now consider the apparatus needed for satellite reception. First of all, we must decide what signals we want to receive. If we are content with the ‘normal’ signals, that is to say the signals intended for reception in a particular country, then a parabolic antenna of 0·7-0·9 m is required. This can be fixed, since only one satellite position is involved and the receiver need only cover half of the 800 MHz band. The 1977 plan has been so arranged that certain transmissions from neighbouring countries with similar cultures and languages can also be received by the same set-up but a larger antenna. I have called these adjacent transmissions, and examples are the UK and Ireland, Germany and Austria, and so on.

The foresight of Arthur C. Clark in suggesting that television pictures by way of a satellite could be sent direct to the viewer's home is about to come true. Whilst the professional communications fraternity have been using satellites for years for point to point communications it is only with the coming of high power satellites will viewers be able to receive pictures without the intervention of a terrestrial common carrier.

The first geostationary satellites were subject to a number of constraints stemming both from the relatively modest performance of the technique available at the time and from the payload capacity of the launchers used. Such constraints were either technological, eg, the modest power levels of the onboard transmitters or the highest usable frequency, or else economic, particularly the cost of placing a kilogram of satellite in geostationary orbit. At the time, these factors entailed the use of high-performance costly ground stations, which could be operated economically only for long-distance (intercontinental) communications between major traffic centres.

Activities in the broadcast of television by satellite have been accelerating rapidly during 1980 and 1981 creating a good environment for the development of successful DBS systems. These include the development of a competitive satellite manufacturing industry, competition in launch facilities, development of a mass-produced direct receiver industry, expanded television programme production and an expanding market for new television services.

Most of the new services and facilities which, we are told, are going to provide us with new images on the TV screen in the next decade, are led by technology rather than by any established need by the viewer or consumer.

In looking at the commercial viability of DBS services it is necessary to consider how the viewer is likely to react, not only with regard to acquiring receiver equipment but also the extent to which he is going to use it.