Leaky feeder

Key takeaways

Leaky feeder belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Leaky feeder to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Leaky feeder from memory before moving on to harder problems.

Reference excerpt

A leaky feeder is a kind of antenna used for communication in mines, tunnels, and other enclosed spaces. The commercial name radiating cable emphasizes that it is designed to radiate, unlike most cables.

Principle A leaky feeder communication system consists of a cable run along tunnels which emits and receives radio waves, functioning as an extended antenna. 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, line amplifiers are inserted at regular intervals, typically every 350 to 500 metres, to boost the signal. 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 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, 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. Antennae (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 for wireless communication between miners. The system is used as a primary communication system with a transceiver small enough to be comfortably worn for an entire shift.

Underground railways The leaky feeder system is used for underground mobile communication in mass transit railways. In Delhi, Hong Kong, and Copenhagen, leaky feeders were installed during construction. This gives emergency services seamless mobile communication from underground to the surface. The London Underground uses a leaky feeder system for its internal communication network Connect. 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 was criticised in the reports from the 7 July 2005 London bombings, where it hampered rescue efforts. In March 2020, two additional leaky feeder cables were brought online in the Jubilee line extension 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 (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. Tyne and Wear Metro was the first railway in the UK to use leaky feeder cables for public mobile phone connectivity, in its city-centre underground tunnels. Initially this was a 2G signal, but then mobile operator EE upgraded this to 4G for their customers. As of 2023, operator Nexus are planning a comprehensive upgrade to mobile data coverage, including in the tunnels. An alternative to using leaky feeder in underground railways is to use Distributed Antenna System (DAS). A DAS system was deployed in some New York City Subway stations by Transit Wireless to provide Wi‑Fi and mobile phone and data coverage for customers.

In-flight wireless networks Leaky feeder antenna systems can also be used to allow use of onboard mobile phones and Wi‑Fi 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 Wi‑Fi coverage using normal access points. Some installations have 50–75 meters of leaky wire connected to the antenna output of each access point.

RFID A leaky feeder modified with metallic strips can be used as a radio-frequency identification (RFID) antenna.

See also Tunnel transmitter Through the earth mine communications

References

External links IWT Wireless Communications and Tracking in Underground Mines - a wireless mesh alternative to leaky feeder Archived 2018-10-25 at the Wayback Machine

Illustrations

Worked examples

Example 1 — a first encounter with Leaky feeder

Start with the simplest possible case. Write down what Leaky feeder claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Leaky feeder before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Leaky feeder ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Leaky feeder

In research: Leaky feeder appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Leaky feeder in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Leaky feeder is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antennas, so understanding it makes those chapters shorter.
In everyday life: Look for Leaky feeder outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Leaky feeder in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Leaky feeder means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Leaky feeder out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Leaky feeder in simple terms?

A leaky feeder is a kind of antenna used for communication in mines, tunnels, and other enclosed spaces. The commercial name radiating cable emphasizes that it is designed to radiate, unlike most cables.

Why does Leaky feeder matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Leaky feeder?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Leaky feeder.