Through-the-earth radio keeps miners in touch

A digital two-way radio system that can send signals from the surface to depths greater than 300 m will allow voice and text communication especially for miners.

Developed by the Los Alamos National Laboratory in the US, this Through-The-Earth Communication system is being made available commercially by Vital Alert Technologies.

The VLF system allows first responders, rescue teams and underground miners to talk to each other in underground railways, tunnels, skyscrapers and mines during emergency situations.

It can also be used by first responders in the advent of terrorism and natural disasters such as hurricanes, earthquakes and floods.

The system uses VLF in the frequency range of 3 to 30 kHz and digital audio compression to transmit voice and data through the earth. Materials such as rock, concrete, metal and high-density ore bodies do not attenuate the signal.

Unlike RF devices, this technology does not rely on line-of-sight transmission or hard wiring. The system can be coupled with conventional RF equipment to provide enhanced communications coverage both above and below ground.

Incorporating Sprint/Nextel i325 mobile phones, supported by Raytheon's JPS Communications ACU 1000 cross band repeaters, the system was demonstrated in a mine used for safety experiments. Several long tunnels of limestone with a tunnel height of about 3 m and an overburden of about 113 m were used to prove the effectiveness of the system.