The Induction System

The equipment operates by creating a weak magnetic field several hundred meters in diameter. A second radio within that field can communicate with the first radio, and under special circumstances can measure the relative position of the two radios in 3-dimensional space.

Operating on two separate frequencies: 35kHz and 185 kHz, we are literally broadcasting from the heart of the Island. These are cave radios, used for radio survey location and cave rescue. This technology allows us to communicate dependably to a depth of -200m in limestone bedrock, results are somewhat degraded when ferric bearing bedrock or power lines encountered and frequencies have to be altered.

The radio and antenna units are compact enough to be carried fairly efficiently to any location, above or below ground. We are using Single Side Band C.B. radios with a drop down circuit allowing us to communicate at the lower frequencies. The antennas are approximately 1 meter sq. in the operating position and collapse to a dimension of 30cm in diameter and 600cm in length. A Pelican Case is used for the surface radio. At present, we are working on a more ergonomic case for the subsurface unit, adapting a section of 255 X 600 cm PVC pipe with screw ends.

We have found it best to have a team of two people at both the underground and the surface radio stations, the second person being the note taker, this is to enable faster relaying of messages, and allow some redundancy with not having to repeat messages. It was also found that a "Coleman" lantern and stove positioned at the underground and surface stations kept the operators warm. Orange juice and soup can be warmed and transported to the incident areas in steel thermoses giving the underground crews sustinence.

It was also found that in a multiple person incident, ( persons separated underground ), it was more efficient to station the radio in a central location and use runners to communicate from the incident area back to the radio.