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The RFM underground radio system is designed
to enable VHF radio frequencies to be transmitted and received
in underground roadways and tunnels up to 25 km in length. The
age-old problem of strata absorption has been overcome by
using a radiating cable with 2 way repeater amplifiers at 500
metre intervals.
The system comprises a Base Station, Radiating Cable (Leaky
Feeder), in line Repeater amplifiers, Passive Splitters,
Terminators and mobile radio transceivers.
Various interconnect facilities are offered to enable
integration to other radio systems and other types of
communication systems.
With the RFM system, GAI-Tronics has taken the opportunity of
using standard off the shelf pocket phones for intrinsically
safe and non-intrinsically safe applications. A rugged, robust
loudspeaking transceiver, Transcom, is offered for mounting on
mobile vehicles such as locomotives, free steered vehicles or
rope driven haulages.
The Repeaters are powered from the base station and additional
power is only needed for complex long distance systems.
Interface circuitry is offered to allow radio telephones to be
used and connection to other types of communication systems
for loudspeaking Public Address.
Base Station
A variety of base stations are offered to suit individual
customer applications. The Base Station houses the necessary
transmitters, receivers and other interface circuitry. Power
for the Repeater amplifiers is supplied from the Base Station
via the radiating cable.
Radiating Cable
The cable is of a co-axial construction specially designed to
allow signals to radiate and allow signals to be accepted from
portable radios anywhere along its length.
Repeaters
The repeater circuitry is the heart of the system. The design
ensures the signal strength's consistency throughout the whole
network. The repeater acts as a two way amplifier
simultaneously capable of handling multiple channels. The
repeaters would normally be spaced at 500 meter intervals.
Passive Splitter
Because most underground complexes have many tunnels, it is
necessary to be able to split the system at roadway junctions.
The passive splitter allows this to happen without significant
loss of signal strength.
Termination Unit
To maintain a balanced system each end of the radiating cable
requires to be terminated. The Termination Unit ensures this
balancing will take place.
Radio Pocket Phone
A variety of radio pocket phones and radio telephones are
available for personnel use, depending upon customer
requirements. These are standard units usually available in
most countries. Frequency selection and mode of operation
requires to be stated when buying independently, or units can
be specified and supplied by GAI-Tronics.
Vehicle Radios
Because of the special nature of this application GAI-Tronics
has a purpose made unit available with a loudspeaker stage and
handset to overcome ambient noise levels.
System Diagram
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customer service: customerservice@gai-tronics.com 
