Wireless Technology
Figure 3: The main elements of an infra-red mobile voice communications system So there are actually a number of areas
where mobile RF radio communications provides a far from satisfactory solution. In many of these cases, infra-red technology can offer short-range mobile voice communications without any of the emission or susceptibility problems associated with radio transmission.
An alternative - Infra-red systems Infra-red systems such as the Azdec Infra- Com from Link Microtek employ digital encoding techniques and a distributed cellular approach to provide multi-channel full-duplex mobile communications for areas as large as 10,000 square metres. The use of encoding similar to CCITT G.711 ensures crystal-clear sound quality, and the signals are completely immune to electromagnetic interference – even severe energy pulses. Furthermore, since there are no RF emissions from the system, it can be used adjacent to the most sensitive electronic equipment without causing any adverse effects. Short-range infra-red is impossible to intercept or jam by any conventional method, and because the system transmits infra-red at very low power, it carries a Class 1 product designation as defined by the EN 60825-1 standard, which means that it presents no health hazard to users. An infra-red mobile voice
communications system consists of a base station, multiple antennas, multiple mobile units and a battery charger. The number of antennas per system is dependent on the coverage area required and whether it is located indoors or in direct sunlight. As the antennas have a very predictable coverage pattern, the envelope of reception can be precisely defined. The antennas are connected to the base station on simple daisy-chain wiring throughout the area of coverage, allowing the system to be readily extended to cover additional zones as required.
The base station acts as the interface between the system’s digital serial bus and the conventional analogue communications circuits at a site. It also supplies stabilised and filtered power to the antennas, thereby ensuring reliable
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operation and immunity to conducted noise. Housed in an IP65 sealed enclosure to protect against the ingress of dust and moisture, the base station is a compact unit measuring 30 x 30 x 18.5cm. It incorporates a number audio interfaces and LED indicators, according to the configuration of the system.
Each mobile unit comprises a headset
with a rechargeable battery pack and operator interface controls. Voice information is encoded within a transceiver module mounted on the headset then transmitted using infra-red to an antenna. The user is free to roam anywhere within the area,
communicating either with other users or, via the base station, with a remote location such as a control room. Various headset styles are available, including versions with belt-mounted battery/control packs, cordless models with the battery pack and controls integrated into the headset itself, single- sided versions for use in control-room applications, and high-attenuation models for use in areas of high acoustic noise. All types incorporate a noise-cancelling boom microphone.
Up to eight individual channels can be
provided within the area of coverage. Systems can also be specified with an additional external input that allows the user to interface with other communications systems such as a telephone exchange or public-address system. In this case, internal communications are heard in the left earpiece while the external input is heard in the right earpiece. In summary, infra-red technology
provides a viable and effective solution for short-range communications in industrial and military applications where operators need to roam from their base position and where RF systems cannot be used due to safety or security considerations. Compared with radio systems, infra-red offers true stealth communications and is completely immune to electromagnetic interference.
Link Microtek |
www.linkmicrotek.com Steve Cranstone is Managing Director of Link Microtek
Components in Electronics December 2011/January 2012 19
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