Specification of radio relay equipment for road tunnels

Having designed, manufactured and helped to install equipment for radio relaying to tunnels and other enclosed areas, the author discusses the shape and performance that can be expected from equipment currently in use. The main units are described with the aid of block diagrams and completed with a brief specification. The basic system of a radio relay to Tunnels requires a unit to receive the radio signal, pass it to an amplifier that raises the signal to a level sufficient to feed a leaky cable suspended in the tunnel and from which the signal radiates to vehicles passing below. The author describes the AM receiver, the AM modulator, the combiner, the FM receiver, and the FM modulator