The through-the-earth communications unit is being developed in conjunction with the CSIRO and will allow miners to transmit signals directly through rock strata to the surface.

Mine Site Technologies said once completed the two-way PED module will transmit wirelessly back to underground base stations, which will then transmit through the rock strata to antennas located on the surface.

The base stations will be designed to withstand the shock of explosions and remain operating on IS battery power, with tests to date indicating the base stations would be able to transmit through at least 600m of rock.

This will provide a two-step, through-the-earth link from a miner underground to the surface in all but the deepest mines. Deeper mines may require an additional repeater "hop" to reach the surface.

Recent testing of the system - completed at BHP's West Cliff Colliery this month - has confirmed the device is capable of two-way, through-the-earth text messaging at a depth of 480m with messages transmitted through the rock strata in five to 10 seconds.

The company said the new system will undergo further testing and approvals before it is made available; however, its compatibility with the ICCL system ensures mines employing the system will not be disadvantaged.