The legal and health aspects connected with the safety for R.F. services are strategic for the project of one transmitting centre. The values of the field strength should be compatible with the security of neighbouring living people and with the house TV set, telephones, and household appliances. Not only the medical aiding equipment but also the pacemaker, hearing aid systems and other personal aids, may suffer from radio-frequencies interference.
The levels indicated in Fig. 29 of § 3.10 are accepted levels to be maintained at the border of the transmission centre land. The above levels are considered suitable for a radioservice and are to be considered valid also for the quality of a radioservice. Consequently, from the above levels one derives the extension of the controlled area and the location of one transmission centre. Naturally, a transmitter centre located inside a city has much more constraints in comparison with a transmitter centre located in the countryside. Each administration or broadcaster may choose the values of the e.m. reference field (Fig. 29), but, if the value is too low: either the radio services do not have the necessary quality (e.g. because the E.R.P. cannot reach the necessary values), or the necessary land extension is too large with consequent high cost for the construction of the transmission centre.
Currently the sensitivity of the people living near the transmitter centres, is very high for possible problems caused by the radio frequency. For legal consideration one clear indication of the perimeter and extension of the controlled area (where the values of e.m.f. are higher or equal to the values of Fig. 29) should be clearly indicated: one fence, one wall or, at least some appropriate signposting, with indication of e.m.f. value, need to be installed.
From urbanization point of view the construction of residential buildings must be forbidden inside the controlled area. The above aspects connected with the e.m.f. must be treated in the same manner as the ambient ecologic, landscape and panorama problems.
to Part 2
1.1 Digital terrestrial television broadcasting in Australia
Australia is served by an extensive network of PAL-B analogue, and more recently by DVB-T digital, terrestrial television broadcasting transmitting sites. A feature of the transmitter deployments in Australia is that a very large proportion of the population receives signals from a relatively small number of high power “main station” transmitters that have large coverage areas, typically 100-150 km in diameter. Radiated power levels at main station VHF Band III transmitters can be up to 500 kW e.r.p for analogue and up to 100 kW e.r.p. for digital. The radiated power levels at main station UHF Band IV and V transmitters can be up to 2 000 kW e.r.p for analogue and up to 1 250 kW e.r.p. for digital.
As a consequence of the sparse distribution of terrestrial transmitter sites, analogue main station assignments in Australia were generally planned on the basis of noise-limited reception rather than interference limited reception. This has meant that the so-called analogue taboo channels (e.g. adjacent channels, image channels and local-oscillator channels) are usually unencumbered by other (out-of-area) TV signals. Most of the population of Australia has access to five free-to-air analogue TV services.
In introducing digital television, Australia has planned for seven digital television networks in most areas - a digital network for each of the existing analogue networks plus two new digital networks. Australian digital television services commenced in metropolitan regions on 1 January 2001 and subsequently have been progressively deployed in regional areas. The relevant federal government legislation stipulated a simulcast period of eight years. During the simulcast period, existing analogue television transmissions have continued and an additional digital signal has been brought into service. The digital service is required to carry a standard definition (SDTV) digital version of the programmes being provided on the analogue service.
In December 2007 the Australian government changed the simulcast period, announcing that 31 December 2013 will be the date by which the last analogue transmitter will be switched off.
The first step in the DTV conversion process was a comparative assessment process that led to the selection of DVB-T (8k carrier mode) as the preferred digital television transmission standard and the determination of system planning parameters such as interference protection ratios and minimum required signal levels. The availability of this information permitted the conduct of a preliminary study of possible DTV channel allocations. The conclusions of this preliminary study showed that it would be possible to allocate a complete TV channel (7 MHz wide in Australia at both VHF and UHF) to each existing analogue service to permit its conversion to DTV as well as provide additional channels for new digital-only services.
In 1998 legislation that set the framework for the establishment of DTV services was passed by the Australian Parliament. In that legislation the government determined that each broadcaster would be loaned spectrum to provide a digital service that matched the coverage of the analogue service as closely as possible. Further legislation was also enacted to establish the detail of the regulatory regime to apply to the provision of digital television and datacasting.
1.3 Simulcast of SDTV and HDTV programmes
The Australian government has been committed to ensuring that digital television would be as affordable as possible. Although broadcasters have been required to provide at least a minimum amount of high definition television programming for those who can afford HDTV sets, they have also been required to provide their broadcast in SDTV format. SDTV programming provides viewers with a picture quality that is generally superior to the analogue television service. Currently two additional SDTV digital-only programme streams are transmitted on national broadcaster networks and three more commercial SDTV programme streams could be available from 1 January 2009. The transmission of SDTV format programming not only provides viewers with the ability to access the additional features of digital broadcasting, but also provides consumers with a digital conversion path that is cheaper than the alternative approach of purchasing a HDTV set or a HD set top box.
HDTV is a key feature of digital terrestrial television in Australia. Broadcasters are required to transmit HDTV programmes for a minimum of 1 040 hours per year. The government has not specified any particular technical parameters for HDTV, and broadcasters have been able to adopt and use of theMPEG-2 MP@HL format for transmission (i.e. 576/50p, 720/50p, 1080/50i). However, Australian broadcasters have expressed a preference that programme production and exchange should be based on 1080i line formats.
By requiring both SDTV and HDTV programming, viewers have been given a choice in digital television products but at the same time allowed broadcasters scope to demonstrate the appeal of HDTV.