![Leaky feeder cable](https://upload.wikimedia.org/wikipedia/commons/8/81/Leaky_feeder_cable.jpg)
A leaky feeder is a
communications
Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inquir ...
system used in
underground mining
Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...
and other tunnel environments. Manufacturers and cabling professionals use the term "radiating cable" as this implies that the cable is designed to radiate: something that coaxial cable is not generally supposed to do.
Principle
A ''leaky feeder'' communication system consists of a
cable
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
run along tunnels which emits and receives
radio wave
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...
s, functioning as an extended
antenna
Antenna ( antennas or antennae) may refer to:
Science and engineering
* Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves
* Antennae Galaxies, the name of two collid ...
. The cable is "leaky" in that it has gaps or slots in its outer conductor to allow the radio 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 signal is usually picked up by portable transceivers carried by personnel. Transmissions from the transceivers are picked up by the feeder and carried to other parts of the tunnel, allowing
two-way radio
A two-way radio is a radio that can both transmit and receive radio waves (a transceiver), unlike a broadcast receiver which only receives content. It is an audio (sound) transceiver, a transmitter and receiver in one unit, used for bidirecti ...
communication throughout the tunnel system.
The system has a limited range and because of the frequency it uses (typically
VHF or
UHF), transmissions cannot pass through solid rock, which limits the system to a
line-of-sight application. It does, however, allow two-way mobile communication.
Due to the signal loss along the feeder, a leaky feeder is usually used for frequencies under 1 GHz. Above that frequency the losses require too many repeaters, thus making other options more effective. Antennas (omni, panel or bi-directional) or even
Distributed antenna systems are more often used for higher frequency bands.
Applications
Mining
Leaky feeders are used in the mining industry as a method of wireless communication between miners. The system is used as a primary communication system which has a transceiver small enough to be comfortably worn on a miner throughout an entire shift.
Underground railways
The leaky feeder system is used for underground mobile communication in
mass transit
Public transport (also known as public transportation, public transit, mass transit, or simply transit) is a system of transport for passengers by group travel systems available for use by the general public unlike private transport, typical ...
railway
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
s. In the
Delhi Metro
The Delhi Metro is a mass rapid transit (MRT) system serving Delhi and its satellite cities of Ghaziabad, Faridabad, Gurgaon, Noida, Bahadurgarh and Ballabhgarh, in the National Capital Region of India. The network consists of 10 colour-cod ...
,
rail transport systems of Hong Kong, and the
Copenhagen Metro
The Copenhagen Metro ( da, Københavns Metro, ) is a 24/7 rapid transit system in Copenhagen, Denmark, serving the municipalities of Copenhagen, Frederiksberg, and Tårnby.
The original system opened in October 2002, serving nine stations on t ...
(Danish: ''CityRingen''), leaky feeders were incorporated in the specification of the capital project and installed during construction. This gives emergency services seamless mobile communication from the underground to the surface.
London Underground
The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
uses a leaky feeder system for its internal communication network ''
Connect
Connect may refer to:
Music Albums
*Connect (album), ''Connect'' (album), an album by Australian rock band Sick Puppies
*''Connect'', album by Mark Farina
*''Tha Connect'', a 2009 album by Willy Northpole
*''Connect'', a 2009 album by Dave Schu ...
''. However, the communication used by the emergency services,
Airwave, was not compatible and did not work below ground. The fact that this situation continued to exist after the 1987
King's Cross fire
The King's Cross fire was a 1987 fire in a London Underground station with 31 fatalities, after a fire under a wooden escalator suddenly spread into the underground ticket hall in a flashover.
The fire began at approximately 19:30 on 18 Novembe ...
was criticized in the reports from the
7 July 2005 London bombings
The 7 July 2005 London bombings, often referred to as 7/7, were a series of four coordinated suicide attacks carried out by Islamic terrorists in London that targeted commuters travelling on the city's public transport system during the mo ...
, where it hampered rescue efforts. In March 2020, two additional leaky feeder cables were brought online in the Jubilee line tunnels between Canning Town and Westminster. One of these cables provided commercial 4G coverage for passengers, both in the tunnels and on station platforms, whilst the second cable provided coverage for the Home Office's
Emergency Services Network
The Emergency Services Network is an LTE radio communications network under development in the United Kingdom to provide unified communication for British emergency services. It is intended to replace the existing TETRA-based Airwave network in 2 ...
(ESN), which is currently being rolled out to replace the ageing Airwave network. This trial section is the first to be brought online as part of a project to provide both commercial 4G coverage and ESN coverage across the entire Tube network.
An alternative to using leaky feeder in underground railways is to use
Distributed Antenna System
A distributed antenna system, or DAS, is a network of spatially separated antenna nodes connected to a common source via a transport medium that provides wireless service within a geographic area or structure. DAS antenna elevations are general ...
(DAS). A DAS system was deployed in some
New York City Subway
The New York City Subway is a rapid transit system owned by the government of New York City and leased to the New York City Transit Authority, an affiliate agency of the state-run Metropolitan Transportation Authority (MTA). Opened on October 2 ...
stations by
Transit Wireless
Transit Wireless is an American telecommunication company founded in 2005, based in New York City. It was formed as a consortium of several entities, including Dianet Communications. It specializes in building wireless communication infrastruct ...
to provide
WiFi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves ...
and mobile phone and data coverage for customers.
In-flight wireless networks
Leaky feeder antenna system can also be used to allow reception of on-board
GSM
The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...
and
WiFi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves ...
signals on passenger aircraft. The weight and space requirements of leaky feeder systems are usually lower than comparable antenna systems, thus saving space and fuel. The even field strengths produced by runs of leaky feeders spanning the entire fuselage improve coverage while requiring less transmitting power.
Industrial buildings
Leaky feeders are used in hotels, warehouses and other industrial buildings where it is difficult to get WiFi coverage using normal
access points. Some installations have 50–75 meters of leaky wire connected to the antenna output of access points.
RFID
Leaky feeders modified with metallic strips can be used as a
Radio-frequency identification
Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects. An RFID system consists of a tiny radio transponder, a radio receiver and transmitter. When triggered by an electromag ...
(RFID) antenna.
See also
*
Tunnel transmitter
A tunnel transmitter allows wireless reception in tunnels. It consists of a receiving antenna which receives the signal to be radiated in the tunnel, and a transmitting antenna installed in the tunnel, which is either a Yagi antenna or a line anten ...
*
Through the earth mine communications
References
External links
IWT Wireless Communications and Tracking in Underground Mines - a wireless mesh alternative to leaky feeder
{{DEFAULTSORT:Leaky Feeder
Antennas