Traditional or wireless systems:
- Magneto phones
- Paging phones.
- Phones that can be operated by voice
- Trolley carrier phone system.
- Hoist rope system.
Wireless Underground Communication Systems
RF Transceivers The RF transceivers, especially for direct gallery communication, are the most popular and widely used equipment in underground mines. Different frequencies, ranging from LF (low frequency) to VHF and UHF (very high frequency), are used in different situations depending on the structure of the mine or the type of extracted mineral.
Low Frequency (LF) Transceivers
The attenuation rate of LF signals through coal is comparatively lower than those with higher frequencies. This can be used to establish communication between trapped miners and rescue teams, as well as determine the exact location of the miner in order to rescue him. The LF frequency range is typically around 30 KHz. Large blocks of coal can transmit the modulated low/medium frequency tone signal over RF signal 457kHz.
VHF (Very High Frequency) Transceivers
VHF (very high frequency) and FM (frequency modulated) transceivers can be used in mines. However, the power output of radio frequencies (RF) signals must be kept low to comply with underground mining safety standards.
UHF (Ultra High Frequency) Transceivers
Attenuation in the UHF band is low in straight areas of mines, but is much higher in corners and when large machinery is in the propagation path. The propagation of UHF signals is impeded by corners and bends in underground mine galleries. Because of the intrinsic safety limit in mines, higher wattage transceivers cannot solve this problem. The active antennas are placed near the turns to amplify the signal.
Waveguides (passage) are created by coal mines. These frequencies range from 200 to 4000 MHz. This allows waves to travel through the tunnel without loss or attenuation. This loss can be as low as 450 to 1000 MHz depending on the tunnel dimension and the distance desired.
Leaky Feeder Radio System
Leaky Feeder is a system that uses the cable’s leakage field to provide two-way voice, data and/or video communication. A Leaky feeder cable can also be called a radiating wire because it is intended to radiate, something that coaxial cables are not supposed to do. Leaky Feeder cables are intended to transmit radio signals out and allow signals in from distant radio transceivers. They can be located between 50 and 200 meters away from the Leaky Feeder Cable. Line Amplifiers or boosters are installed along the Leaky feeder cables, approximately every 350m. This is to sustain signal levels over long distances. One Leaky Feeder Cable is a mine-wide antenna that acts as a communication highway. It eliminates the need for multiple hardwired cables or signal wires to be installed and maintained.
This post was written by Justin Tidd, Director at Becker Mining Communications! For over 15 years, Becker Communications has been the industry’s leader in Tunnel communication system and electrical mining communication systems. As they expanded into surface mining, railroads, and tunneling they added wireless communication systems, handheld radios, tagging, and tracking systems, as well as gas monitoring.
