Poynting has developed a range of antennas specifically designed for communication in mines or tunnels. The antennas were designed to have a low cross-section and to be mounted close to the roof or side of the tunnel. These antennas operate in the 900, 1800 and 2400 MHz bands.
The first two antennas that were developed were for the 2400 MHz band and consisted of helical antennas that are either dual-way or one-way. The 2 m dual-way antenna consists of two helices that are arranged in such a way that the radiation pattern has two principal lobes each pointing 180° from each other. This antenna is thus ideal for providing coverage down long straight tunnels (road, rail or mine tunnels), says Poynting. The antenna is enclosed in a rugged, waterproof plastic housing (with a diameter of 120 mm) and is therefore able to withstand the harsh environment for which it was designed.
The other antenna is a unidirectional version constructed using one helix only. Two one-way antennas can be joined using a splitter to construct an access point at a tunnel junction or bend. The gain for the dual-way 2,4 GHz antenna is between 16 and 17 dBi, and the typical beamwidth 24-27°.
Measurements were performed in the AngloGold Kopanang Mine in Orkney on two occasions and, according to Poynting, the results exceeded all expectations. Two dual-way antennas were used for space diversity and the communication range exceeded 400 m either way (800 m of haulage for one access point). Such coverage results in a cost per metre that is lower than a typical leaky feeder. With 11 Mbps data rates (supported under IEEE-802.11) achievable, vastly superior bandwidth and performance is obtained. In addition to high-speed data transfer, wireless LANs can carry digital voice using IEEE- 802.11VoIP, handheld telephones and video. Normal quality video (as seen on a television) requires 2 Mbps using MPEG2 compression. This frame repetition rate is much higher than is normally required of industrial applications. Slower repetition rates, lower resolution and/or lower data rates, make many simultaneous video and voice links possible on a single network. Also, IEEE-802.11 WLAN systems are cellular in nature and allow users to roam from access point to access point.
International interest
At the request of Grintek Communication Systems' Gerbrandt Steyn, antenna prototypes for the 1800 MHz frequency were developed. GCS and Cell C then ran successful trials in the DuToits Kloof Tunnel. With a dual-way antenna placed in the centre of the tunnel, coverage of 2 km to each side was received, resulting in the complete 4 km length of the tunnel being covered. Vodacom is also undertaking underground trials for cellular communication in mines at an AngloGold mine.
Managing director of Mine Radio Systems, Kenneth Morrell, invited Poynting to give a presentation of mining-related experience and antennas to representatives of the company. MRS is a Canadian-based company with branches in South Africa and Australia. According to the company's system specialist, Mark Montpellier, it has a similar project in Canada that will benefit greatly in using these antennas, while Patrick Waye, president of MRS, said he would like to see the MinePoynt integrated with its Ethernet Leaky Feeder system. The company also foresees great demand for underground antennas from Australia.
For more information: Poynting Antennas, 011 262 5155, Dr Andre Fourie, andre.fourie@poynting.co.za, or Claire Nitch, sales@poynting.co.za
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