Abstract :
The purpose of this study was to obtain information regarding single and multi channel VHF and UHF radio signal booster systems which have been constructed in subway and highway tunnels in Europe and to disseminate this information in the U.S.A. Early in 1977, while the author was engaged in designing a UHF radio system for a subway, he learned that low power radio signal booster systems using a "daisy chain" of amplifiers (similar to a CATV trunk line) were being used in coal mines in the United Kingdom and that London Transport was installing a signal booster system in the Bakerloo Tube to replace a conventional system that had used a base station to feed a tee section of leaky coaxial cable. This new system used low power signal booster amplifiers spaced 500 meters apart to compensate for the attenuation in the leaky coaxial cable antenna system. The design was based upon similar systems which were used in coal mines in the United Kingdom and it afforded a number of advantages over conventional multiple base station systems used in the U.S.A. such as: • Signal strengths throughout the tunnel system are uniform. • Only one base station per radio channel is needed for a typical subway; this substantially reduces costs for renovating space for radio systems in existing subways and also eliminates hetrodyne interference that occurs at transitions between the ends of adjacent antennas. • If wide band class A linear signal booster amplifiers (similar to CATV line amplifiers) are used, a number of channels can be readily and more economically provided for train communications, maintenance, security, fire, police and para-medical services. • Fewer control circuits are needed and central control facilities and operations are simpler. • Equipment, installation and operating costs are lower. In August, 1977, the author visited Dr. D.J.R. Martin, co-inventor of the "daisy chain" concept and London Transport and obtained information regarding the VHF radio system in the Bakerloo Tube which was summarized in a paper that he presented at the 28th IEEE Vehicular Technology Conference at Denver, Colorado, in March, 1978. A somewhat similar VHF signal booster system was designed for the new U- -1 subway in Vienna by German and Austrian engineers who evidently were not aware of the work that had been done in England. The Vienna system was visited in 1978 shortly after the subway was commissioned and its performance was superior to conventional systems used on other subway lines. The subways in Munich and Milan also were visited, but they used conventional base stations to feed tee sections of leaky coaxial cable antenna. A unique multi-channel radio signal booster system for extending AM and FM broadcasting and seven two way VHF public safety channels into two 395 meter highway tunnels in Brussels was visited in 1979 and the designers of the system were interviewed. A single discone antenna constructed of meta½ rods is used for both transmitting and receiving. The Swiss Posts, Telephone and Telegraphs (PTT) authority in Switzerland has developed an eleven channel VHF two way signal booster system for their long highway tunnels. FM broadcasting (87.6 - 104 MHz) as well as two way VHF radio telephone, police, fire and maintenance services will be accommodated. A list of persons in Europe who are engaged in development research or operation of radio systems using signal boosters (in-line repeater amplifiers) in tunnels is included in Appendix 1.
