Tests of distributed antenna system along a railway test track

A distributed antenna system, 900 ft long, was installed on a cable tray alongside the BART test track. Two CATV coaxial cables were used, one for transmitting (Tx) signals to the train and the other for receiving (Rx) signals from the train. Four mobile whip antennas, spaced 300 ft apart, were used for transmitting, and three similar antennas were used for receiving. By using separate transmitting and receiving cables, possible intermodulation and spurious signals were isolated from the receiving cable. Tests on a VHF channel demonstrated that 2 mW radiated power from the Tx antennas afforded adequate signal levels inside a train, and 80 mW from a simulated portable on the train afforded ample signal strengths to the Rx antennas. The radiated signals were confined to a narrow region along the tracks, thereby conserving radio spectrum