Leaky Feeder Radio
There are various methods available for underground radio systems for the distribution of Voice & Data, but the most versatile and reliable system is the so-called "Leaky Feeder" system. The Leaky Feeder cable or backbone is analogous to a surface antenna system.
A good leaky feeder system will provide the basis for not just basic two-way voice and data applications, but allow full telemetry control of remote equipment, such as pumps and fans.
The most effective and universally accepted frequency band for two-way voice, data and video is VHF. These frequencies cannot penetrate rock due to the high level of attenuation that they suffer, communication is primarily reliant on line of sight. An example of this problem is the inability of a commercial radio signal to broadcast through tunnels. On the surface, line of sight transmission is feasible, however, this is not always the situation in a mine.
To allow radio frequencies to function underground, it is necessary to replace a standard surface antenna system with a cable network. The cable networks can be installed to effectively radiate the signal throughout the mine. The cable utilised is designed to "leak" signal, which allows radio transmissions to both leak from the cable and also enter the cable.
The inherent loss of signal must be compensated for and this is achieved by the insertion of line amplifiers. The amplifiers are designed to compensate for a certain length of cable. Correct installation of the system will ensure that a consistent signal level is maintained throughout the network, hence throughout the mine.
Leaky Feeder technology is a combination of Leaky Feeder cable and Amplifiers. Other components can be added, but the backbone of the system comprises only these two elements.