Propagation and radiation of VHF radio signals in motorway tunnels

A functional land mobile service requires that radio communications be ensured outside as well as inside of motorway tunnels. An experimental investigation about radiation and propagation of VHF radio waves in a 150-m motorway tunnel is presented. Three radiating systems, to convey radio signals into and out of the tunnel, are examined: antennas slotted coaxial cable balanced two-wire line. Results are presented in the form of total attenuation (total attenuation is the transmission loss (radiation and heat loss) plus coupling loss) versus distance curves and also as cumulative distribution curves of coupling loss, in the case of the radiating lines. A comparison among these three systems is also given.