Wireless – the cable of the future?
As one engineer said at a recent seminar arranged by Lapp Kabel “I can touch it!” Perhaps he has not considered the risk of cable theft if the connection runs between buildings; even private property is not immune to the theft problem.
Then there is also lighting to be considered – nearby strikes can introduce large currents in a lengthy cable run unless sophisticated lightning and surge protection is fitted. Considering this and factors such as the increasing cost of cabling makes the wireless option more attractive. At current cost levels wireless breaks even with a cable installation of around 500 m.
Radios used in place of data cables can reach distances of up to tens of kilometres depending on the terrain, the output power of the radio and the antenna deployed. And if that is not long enough, radios can be set to act as repeaters to extend the range over just about any distance.
Lapp Kabel supports radio data modems engineered and manufactured by Satel, a company that hails from the town of Salo in Finland, also the home of Nokia. Salo is considered the telecon valley of Finland where most engineers eat and sleep radio!
Radio modems are deployed in a multitude of applications, from airports monitoring various control applications to industrial plants to set up internal data transfer networks. Also in cities for city-wide alarm networks and location data-based traffic monitoring systems to enable smoother running of public transport and timetable information at bus stops, much like the rapid bus transport systems one sees in major cities around the world and soon also in Johannesburg, Pretoria and Cape Town. The control of transport is an interesting application as the smooth running of buses during peak traffic times can be regulated by facilitating green robots along the bus route.
One of the concerns of engineers who are new to wireless connections is the question of whether radio modems have sufficient tolerance to interference from other radio systems in areas where there is a high level of radio frequency pollution? During the many field trials in major city applications the Satel design has proved to have superior immunity and coupled with the sophisticated signal encoding and decoding has shown exceptional reliability.
Satel radio modems are available to operate in both the licensed and unlicensed VHF and UF spectrum and a large range has been type approved by the Independent Communications Authority of South Africa (ICASA) for deployment in South Africa. The radios also comply with the EU directive on the restriction of hazardous substances (RoHS).
In applications where line of sight is an issue, UHF radios can be used which include diversity reception. It is not necessary to have a direct visual connection between the master station and the moving substation because the radio signals transmit by reflecting from buildings and geographical features such as hills. As the transmission speed of radio signals is the same as that of light, signals reflected from various objects arrive at different times.
The signals at the receiving antenna come in at different phases so even in the worst case two opposite but equal signals cancel each other out, causing fading. The dips in the signal appear with half-wave intervals. The reliability of the signal thus depends on the position of the receiving antenna. By setting up two antennas at the receiving end at least three quarters of a wavelength apart, the fading is overcome. In the Satelline range models are available that deliver 10 W and have two built-in receivers. The modem automatically chooses the best signal for greater reliability.
A network managed system further improves a wireless system’s reliability by allowing problems to be anticipated and often resolved without needing to visit the site. Vital network statistics are instantly accessible from the network PC.
When opting for a wireless system the concern is often the delay by Icasa in licensing the frequency. If there is an urgent requirement Lapp Kabel has an option where they will install a system on a non-licensed frequency and replace it once the licence has been issued by Icasa.
Wireless versus wired – give your views
EngineerIT
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