Radio coverage for road and rail tunnels in the frequency range 75 to 1000 MHz

Leaky cable tunnel radio systems for the 75 MHz to 450 MHz frequency bands have been successfully used in Switzerland for 10 years. Road tunnels up to 16 km long have been equipped with VHF leaky cable systems using up to 24 cascaded wideband amplifiers. More recent systems use dual-band amplifiers (75/150 and 450 MHz). Condensation can be a problem; therefore the effect of moisture on the cable attenuation has to be carefully assessed. Disaster-proof systems with two cables running in opposite directions can provide radio coverage even when both cables are interrupted. At 900 MHz, antennas instead of leaky cables have proven to be a more economical solution. However, the effect of the traffic density, especially the filling factor, has to be kept carefully under control. For rectangular road tunnels, a spacing of about 4 km between base stations is possible.<
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