Leaky feeder
Encyclopedia
A leaky feeder is a communications
system used in underground mining and other tunnel environments. It consists of a coaxial cable
run along drivages which emits and receives radio wave
s. The cable is "leaky" in that it has gaps or slots in its outer conductor to allow signal to leak into or out of the cable along its entire length. Because of this leakage of signal, line amplifiers are required to be inserted at regular intervals, typically every 350 to 500 metres, to boost the signal back up to acceptable levels.
The system has a limited range and because of the high frequency
it uses, transmissions cannot pass through solid rock
, which limits the system to a line-of-sight
application. It does, however, allow two-way mobile communication.
This system is also used for underground mobile communication in mass transit railways. In Hong Kong
the leaky feeder aerial was incorporated in the specification of the capital project and installed during construction. This allows emergency services seamless mobile communication from the underground to the surface.
In London
, London Underground
uses a leaky feeder system for their internal communication network Connect
. The emergency services' communications system however was not compatible and did not work underground. That this situation continued to exist after the 1987 King's Cross fire
was criticised in reports into the 7 July 2005 London bombings
, where it hampered rescue efforts.
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
system used in underground mining and other tunnel environments. It consists of a coaxial cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
run along drivages which emits and receives radio wave
Radio Wave
Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
s. The cable is "leaky" in that it has gaps or slots in its outer conductor to allow signal to leak into or out of the cable along its entire length. Because of this leakage of signal, line amplifiers are required to be inserted at regular intervals, typically every 350 to 500 metres, to boost the signal back up to acceptable levels.
The system has a limited range and because of the high frequency
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
it uses, transmissions cannot pass through solid rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
, which limits the system to a line-of-sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
application. It does, however, allow two-way mobile communication.
This system is also used for underground mobile communication in mass transit railways. In Hong Kong
Rail transport in Hong Kong
Hong Kong's rail network comprises public transport trains operated by MTR Corporation Limited . The MTRC operates the metro network of Hong Kong and the commuter rail network connecting the northeastern and northwestern New Territories with the rest of Hong Kong...
the leaky feeder aerial was incorporated in the specification of the capital project and installed during construction. This allows emergency services seamless mobile communication from the underground to the surface.
In London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
, London Underground
London Underground
The London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England...
uses a leaky feeder system for their internal communication network Connect
Connect Project
The Connect Project is a project name for a radio communications system developed for Transport for London. The system will introduce Terrestrial Trunked Radio technology to the London Underground.-Overview:...
. The emergency services' communications system however was not compatible and did not work underground. That this situation continued to exist after the 1987 King's Cross fire
King's Cross fire
The King's Cross St. Pancras tube station fire was a fatal fire on the London Underground. It broke out at approximately 19:30 on 18 November 1987, and killed 31 people....
was criticised in reports into the 7 July 2005 London bombings
7 July 2005 London bombings
The 7 July 2005 London bombings were a series of co-ordinated suicide attacks in the United Kingdom, targeting civilians using London's public transport system during the morning rush hour....
, where it hampered rescue efforts.