Induction radio system for vehicles

Claim 1

An induction-radio system for vehicles following a track comprising a transmission line positioned in parallel with a track and consisting of two conductors helically wound with an equal and constant pitch around a longitudinal axis and axially separated by one-half of said pitch, a transmission signal source connected to said transmission line to transmit an intelligencemodulated carrier-frequency current thereon, antenna means mounted on a vehicle following said track and adjacent said transmission line for continuous coupling with the magnetic flux produced by the flow of said carrier current in said transmission line, a receiver on said vehicle connected to said antenna means, said antenna means having at least one pair of elements positioned relative to each other and said transmission line to receive said carrier current respectively by electromagnetic induction coupling with a spatial phase shift of one-fourth the transmission line winding pitch whereby the receiving level of one of said elements is Always maximum when the receiving level of the other element is minimum, and phase-combining means operable to phase shift the received signal of one of said elements by 90* over the signal band of the carrier frequency and to add to it the received output of the other element to obtain an output having a uniform signal-receiving level when said vehicle is moving.