Tunnel transmitter
Tunnel radio systems, also tunnel stations, are technical facilities that enable in tunnels or mines a wireless radio communication.
The strong attenuation of radio waves in the ground is not possible radio coverage of a tunnel from the outside. Exceptions are only a short tunnel (typically tunnel lengths below 500 m ) or tunnel entrances, which can be supplied by directional antennas that are installed on Tunnelvorportal.
Through tunnel radio systems tunnel systems with radio, public mobile radio (GSM, UMTS ) mobile radio can be supplied ( eg for road service ) and bad radio for police, fire and rescue services. Special tunnel radio systems are used for the operation of radio in mines.
Construction of tunnel radio system for road tunnels
High-level roads ( ie motorways and expressways ) with a tunnel length of about 500 m are generally equipped with tunnel radio systems.
The typically required for road tunnels frequency range is in the 70 -cm, 2 m, 4 m band and the FM broadcast band. In addition, tunnels are partially supplied with mobile frequencies (GSM or UMTS).
Systems according to the current state of the art consist of the following components:
- Free-field antennas ( for coupling or decoupling of the radio signals from the tunnel in the free field)
- Tunnel radio headend (central processing unit, which transmits the RF signal from the free field to the tunnel stations and receives from the individual stations tunnel )
- Tunnel stations ( spaced from 500 to 1000 m HF-Empfangs-/Verstärkereinheiten, the sections provide the tunnel )
- Antenna system ( (also leak or cable slot cable called emitter cable) for frequencies up to about 1 GHz and higher frequencies pendulum antennas) in the tunnel
Systems of this type are in sectors, which are served by each station, a tunnel divided. The tunnel stations are usually connected in a star shape over fiber-optic cable (FOC) with the head station. Signals that are received in a sector of the local tunnel station will be implemented by means of electro - optical transducer to a fiber optic signal and transported to the headend. In the opposite direction ( head station → Tunnel Station ) those signals are transmitted that are broadcast in the tunnel.
The tunnel is powered by lamp cable antennas generally. For frequencies > 1 GHz and directional antennas (eg, satellite dishes ), since radio waves with frequencies > 1 GHz spread well into the tunnel instead of radiating cables. Special radiators are coaxial cables that are laid in the control of the tunnel ceiling parallel to the tunnel profile and emit and receive a signal over the entire length can ( Typical diameters of the radiating cable 0.5-1.5 inches).
Construction of tunnel radio system for metro and railway tunnels
Modern tunnel radio systems for railway tunnels do not differ in their technical design or hardly any of those for road tunnels.
The difference to road tunnels is only in the usable frequency range. On the supply of broadcast signals is omitted in metro and railway tunnels in general.
Subway tunnel or underground running metro stations are generally supplied with GSM and UMTS to the passengers mobile reception with conventional mobile phones such as at the surface allow. These mobile systems do not act in all cases as a relay station, but are run as a standalone base station.
On Railroads GSM -R is increasingly being used ( inter alia for ETCS Level 2 ), which makes a radio coverage in the frequency range 876-925 MHz is required.
Other embodiments
Earlier tunnel radio systems (installation before about 1995 ) for road and railway tunnels were mostly built in the so-called cascade technique. In this technique, the transmitted signal is coupled at one end in a slot -ribbon cable and is refreshed at intervals of typically 250-500 m by RF amplifier. Disadvantage of this variant is caused by repeated reinforcement worse radio quality and increased interference range in case of errors (faults in the cable or in one of the amplifiers affect the entire subsequent underground section ).
Special shapes
Tunnel transmitter for radio stations can be performed in rare cases, for long and medium wave. An example of this is found in the Dartford Tunnel in London, where the program " Virgin Radio " will be provided in the medium wave and long wave program of the BBC for the motorist inside the tunnel.
In the area of non-public broadcasting operation in mines and mining equipment is in use as part of the operating cycle.
Literature sources
- Shuqi Wang, Xiaobing Han: Influence of Transmitter Position and Dielectric Constant on Electromagnetic Waves Propagation in Mine Tunnel. 2009, doi: 10.1109/MMIT.2008.40.