Traditional terrestrial macro networks for radio and cellular do not provide coverage under the surface of the earth. Communications, however, are critical. Mining environments require radio communications for worker safety and require data communications to support diagnostic systems, cameras, logic controllers, and even autonomous and tele-remote vehicles. So, what kind of equipment works in a mine?
Mining communications equipment must be reliable, robust, and ruggedized. One expects a mine to be dusty and loud, but it is also sweltering. Water is required for plumbing and cooling. Add in temperatures which reach up to +55 ⁰C as the mine descends and trap the heat and moisture in some tunnels which are only 18’ x 18’ and humidity cannot easily escape. To provide protection against the dust and humidity, an International Protection rating of IP67 (dust tight / water proof up to 1 m) is recommended. Beyond atmospheric ‘wear and tear,’ the chances of access points being bumped or hit are high. Ruggedized equipment designed to withstand shock and vibration will function better and longer. In terms of a total communications backbone, mine communications are best provided with passive or a hybrid DAS.
There are two main ways you can engineer coverage in the Passive and Hybrid DAS networks.
Tappers, splitters, cable, and antennas
One way to implement passive DAS is through. Directional antennas are highly recommended for providing coverage in a tunnel. Yagi antennas are most common for single-band implementations as they are small, cost-effective and have decent gain. Planar array antennas, corner reflector antennas, and dishes have higher gain but are too large to implement in a sub-terranean space.
The other common type of DAS used in tunnels is run on radiating cable. Radiating cables allow the signals to ‘leak’ or radiate from the cable. Radiating cable is more difficult to install and has lower dynamic range but it is broad band and it has a more uniform coverage for small areas such as tunnels.
There are typically four different sizes of radiating cable; ½”,⅞”, 1 ¼” and 1⅝”. Each of the various sizes has slightly differing characteristics, but for the most part, the larger the cable, the more expensive and the more difficult it is to install. Installation of long runs of radiating cable typically requires a reel mounted to a truck in order to unspool and mount properly. However, larger cable has less loss per 100m than the smaller cables which makes the larger better suited for longer tunnels.
There are, of course, advantages and disadvantages to both types of solutions.
- More economical
- Easier to install
- Coverage is not uniform as driving away from an antenna is not the same as driving toward
- Difficult to find multi-band, high gain, directional antennas with a small form factor to protect it from large machinery
- More expensive
- More difficult to install
- More uniform coverage
A Hybrid Approach
There are benefits to completing a hybrid of both radiating cable and using discrete antennas, especially since the nature of the mine is that the extraction areas are always advancing. For instance, in the office spaces, electrical rooms, mechanical rooms, and break rooms, discreet omni antennas should be used. For the areas of advancing mine/tunnel, it is possible to iteratively aim a Yagi antenna down/up the tunnel and, then when a certain portion of the tunnel is complete, roll out a 100m, 150m, 200m of radiating cable and then relocate the Yagi to aim down the tunnel at the end of the radiating cable as the tunnel development progresses.
Mines are complicated environments in constant flux. The on-site personnel require the basics of RF knowledge and detailed equipment and parts knowledge. Ensuring those personnel can keep communicating requires good base engineering, a system designed with a solid backbone that can extend as the mine advances.
If you are looking at implementing an industrial DAS, please contact Cartel Communication Systems. We are happy to engineer and implement a solution that will work for your environment.
Wallace Hollingshead, Engineering Manager