What is Leaky Feeder Cable
Leaky feeder cable is a type of coaxial cable that differs from traditional coaxial cables in that the outer conductor surface has periodic slots or gaps (such as spiral or figure-eight shapes), which allow signals to enter and exit the cable as they are transmitted. This design enables it to function as both a transmission line and an antenna. Leaky feeder cable was originally designed to provide radio signal coverage for tunnels and/or complex structures.
Leaky Feeder Cable Specifications：
Leaky feeder cable specifications vary by model but typically include a characteristic impedance of 50 or 75 ohms, a velocity of propagation around 86-88%, a capacitance of approximately 76 pF/m, and an operational temperature range of -40°C to +85°C. Construction involves an inner conductor, a dielectric, a slotted or apertured outer conductor to allow signal leakage, and a protective outer jacket, with dimensions often include 1/2", 7/8", 1-1/4" and 1-5/8"
|
Size |
|
1/2" |
7/8" |
1-1/4" |
1-5/8" |
|
Max. Operating Frequency |
MHz |
6000 |
1000 |
1000 |
1000 |
|
Impedance |
Ohm |
50 +/- 2 |
50 +/- 2 |
50 +/- 2 |
50 +/- 2 |
|
Velocity, percent |
% |
88 |
89 |
89 |
90 |
|
Capacitance |
pF/m (pF/ft) |
76 (23.2) |
75 (22.9) |
75 (22.9) |
73 (23.2) |
|
Inductance, uH/m (uH/ft) |
µH/m (µH/ft) |
0.19 (0.058) |
0.188 (0.057) |
0.188 (0.057) |
0.19 (0.058) |
|
DC-resistance inner conductor, ohm/km (ohm/1000ft) |
Ω/km (Ω/1000ft) |
1.57 (0.48) |
1.74 (0.53) |
0.84 (0.26) |
1.62 (0.49) |
|
DC-resistance outer conductor, ohm/km (ohm/1000ft) |
Ω/km (Ω/1000ft) |
3.48 (1.06) |
2.52 (0.77) |
1.85 (0.56) |
1.47 (0.45) |
|
Stop bands |
MHz |
None |
240-300, 500-590, 750-860 |
240-300, 500-590, 750-860 |
240-300, 500-590, 750-860 |
|
Frequency Selection |
MHz |
600, 900, 1800/1900, 2200, 2400, 2500, 2700, 6000 |
600, 900 |
600, 900 |
600, 900 |
The Different Between Leaky Feeder Cable and RF Feeder Cable
1. Definition
Leaky Feeder Cable: A specially designed feeder cable that allows a portion of the signal to ‘leak’ along the length of the cable, commonly used for wireless signal coverage over large areas.
RF Feeder Cable:Primarily used for transmitting radio frequency signals, typically a coaxial cable with excellent shielding performance, specifically designed to minimise signal loss.
2. Working Principle
Leaky Feeder Cable:The outer layer of the cable has small holes or gaps that allow signals to radiate out at certain points along the cable, thereby covering the surrounding area. This design enables signals to propagate in specific areas along the cable's path.
RF Feeder Cable: Primarily used for transmitting radio frequency signals, typically a coaxial cable with excellent shielding performance, specifically designed to minimise signal loss.
3. Application Scenarios
Leaky Feeder Cable: Commonly used in underground parking lots, tunnels, large buildings, and other scenarios requiring coverage of extensive areas, especially in areas where signals are difficult to reach.
RF Feeder Cable: Widely used in wireless communication base stations, television broadcasting, satellite communication, and other applications requiring efficient signal transmission.
4. Signal Coverage
Leaky Feeder Cable: Provides uniform signal coverage along the entire cable length, suitable for distributing wireless signals over large areas.
RF Feeder Cable: Provides point-to-point signal transmission, typically used to connect transmitters and antennas, with signal coverage range dependent on antenna performance.
5. Design and Structure
Leaky Feeder Cable: Features specific leakage points in its design and may have a more complex structure to enable effective signal radiation.
RF Feeder Cable: Typically a coaxial cable, with a focus on signal integrity and low-loss design.
Leaky Feeder Cable Application
If you drive through tunnels such as the Dartford Tunnel and your car radio still receives a signal, this is likely provided by a leaky feeder cable.Additionally, the Channel Tunnel has its own radio communication system that covers the entire route from the UK to France, including the passenger terminals at both ends. This system uses leaky feeder cable within the tunnel and traditional antennas at both ends to cover the passenger terminals. Due to the tunnel's immense length (over 25 miles), multiple bidirectional amplifiers are regularly deployed along the entire tunnel length to enhance signal strength.
