No. 546 December 2011 

Medium Frequency Mine Emergency Communications—An Emerging Technology 

Objective 

To evaluate and develop medium frequency 

communications technology for emergency underground 

mine communications. Medium frequency 

communications systems do not require a powered 

underground infrastructure to be installed for operation, 

and may therefore provide a higher degree of survivability 

after a mine disaster than other types of systems. 

Background 

In June 2006, Congress passed the Mine Improvement 

and New Emergency Response Act (MINER Act), 

mandating that underground coal mines provide 

emergency response plans that include two-way wireless 

communications and electronic tracking systems within 

three years. To satisfy that legislation a wide variety of 

communications systems have been developed to meet the 

guidance set forth in the Mine Safety and Health 

Administration (MSHA) program policy letters that 

followed. In the years following the MINER Act of 2006, 

the National Institute for Occupational Safety and Health 

(NIOSH) supported the development of different types of 

communications and tracking technologies. 

Most underground mine communications systems use 

hand-held, high frequency radios similar to systems used 

on the surface. These high frequency systems require the 

installation of underground powered infrastructure that is 

susceptible to damage from events such as roof falls and 

explosions. In contrast, medium frequency (MF) systems 

use existing mine conductors for communications, such as 

underground transport rails and mine power cables, which 

have a better chance of remaining intact after a mine 

disaster. 

In December 2006, NIOSH entered into an interagency 

agreement with the US Army to evaluate communications 

technology originally developed by Kutta Technologies 

for the military, with the goal of adapting that technology 

for mine emergency communications. 

Medium Frequency Operation 

MF systems operate between 300 and 3,000 kilohertz 

(kHz). Underground, MF signals have a unique effect that 

makes them parasitically couple to nearby metal 

conductors. Unlike most traditional high frequency 

systems, MF signals can travel long distances 

underground without aid from powered infrastructure. 

MF signals can propagate onto many different kinds of 

common conductors found in a mine ranging from page 

phone lines to metal pipes or track (see Figure 1). 

Figure 1. Medium frequency (MF) communications on existing 

conductors (highlighted green) in a mine.

Once a medium frequency signal couples to a good 

conductor, it can travel several miles. Because MF signals 

can travel over multiple conductors at the same time, they 

may provide more diverse paths for emergency 

communications to propagate out of the mine. This could 
increase the chances of successful communications in a 

situation where the mine’s power and its infrastructure 

become disabled. 

An underground MF communications system consists 

of as little as three parts: an MF transmitter, a conducting 

medium, and an MF receiver (see Figure 2). An MF 

transceiver can function as the transmitter and receiver, 

allowing miners to transmit and receive with the same 

device. In order to communicate, miners should be in the 

same entry as the conductor on which they intend to 

transmit and receive MF communications. The closer the 

MF radio is to the conductor, the further the signal will 

travel down that conductor. This holds true for both 

sending and receiving MF signals. 

Figure 2. A simple example of MF communications. 

Test Results and Status of MF Technology 

The first MF radio prototypes were delivered to 

NIOSH in 2009 by Kutta Technologies, Inc. The purpose 

of the prototypes was to determine if the technology could 

be packaged with an omnidirectional antenna, using a 

small battery operating at intrinsically safe levels, and still 

achieve satisfactory performance. The prototypes were 

tested in several underground coal mines. In one coal 

mine, it was observed that the MF signal traveled for over 

two miles (the maximum extent of the mine available 

during the testing period). Observations in some coal 

mines have shown that MF signals can travel as far as five 

miles without any amplification from powered 

infrastructure. It should be noted that each test was 

dependent on the specific mine environment, and that 

configuration of the metal conductors can affect the 

overall performance. 

These tests also demonstrated that MF could be 

interfaced with other existing primary communications 

systems such as ultrahigh frequency (UHF) leaky feeder. 

Kutta Technologies developed an MF-to-UHF bridge that 

allows miners to use the same hand-held radio they use 

with a leaky feeder system (see Figure 3). The MF-toUHF bridges are installed in fixed locations near the leaky 

feeder cable. 

Figure 3. A simple example of an MF-to-UHF bridge. 

By mid-2010, portable MF radios and fixed-location 

MF-to-UHF bridges were approved by MSHA for 

permissibility (see Figure 4). The size of a portable MF 

radio is 12 x 12 x 6 in, which is sufficiently compact for 

the radio to be carried to the face area, but not small 

enough to be worn on the miner. One potential way to 

ensure availability would be to store the MF radios at 

strategic areas and carry them for use during escape along 

a nearby conductor. Several operators have already 

installed MF radios and bridges in their underground coal 

mines for use during a mine emergency. 

The technology described in this article is available 

from Kutta Technologies (http://kuttatech.com/). 

Figure 4. Permissible medium frequency radios.

For More Information 

For more information on this technology and its use, 

contact Nick Damiano (ndamiano@cdc.gov) or the Health 

Communications Coordinator (OMSHR@cdc.gov), 

NIOSH Office of Mine Safety and Health Research, P.O. 

Box 18070, Pittsburgh, PA 15236-0070. 

To receive NIOSH documents or for more 

information about occupational safety and health 

topics, contact: 1-800-CDC-INFO (1-800-232-4636), 

1-888-232-6348 (TTY), e-mail: cdcinfo@cdc.gov, or 

visit the NIOSH web site at http://www.cdc.gov/niosh.

Mention of any company name or product does not 

constitute endorsement by the National Institute for 

Occupational Safety and Health.

DHHS (NIOSH) Publication No. 2012–110