Radio in the London Underground

The London Underground has had a single-channel radio system in service for over a decade. This is now being upgraded by the addition of further channels to serve police, fire and ancillary services. The stations, some of them very deep, also have to be fully covered. Those channels requiring universal cover must be in complete synchronism throughout, while the cover of others must be restricted to avoid clashes between their separate uses. This has necessitated development of new techniques including a channel-selective filter, but the basic infrastructure of leaky cables and in-line repeaters is being substantially preserved. The new channels will work exclusively to low-power handportable sets carried in many cases by personnel traveling on trains. Covering the station areas has involved the development of a multinodal principle for the leaky-feeder layout, and except for the UHF cover of the most extensive stations it is proving possible to avoid use of in-line repeaters in these situations