INDUCTIVE CARRIER COMMUNICATION SYSTEMS

摘要

INDUCTIVE CARRIER COMMUNICATION SYSTEMS A communication system for the transmission of the sound portion of motion pictures or the like in drive-in theaters directly to automobile radios by means of an induction cable buried beneath the ground in the reception area in which automobiles viewing the motion picture are to be parked. The cable is of such design that when properly positioned and combined with an amplitude-modulated radio frequency signaling means, a relatively uniform amplitude-modulated electromatic field of the desired strength and of a frequency which is within the normal reception range of car radios (i.e. the standard broadcast band) is established throughout only the area where the automobiles are parked. To limit signal reception outside the designated parking area of a drive-in theater an interfering signal is transmitted by coupling audio-modulated radio-frequency energy to nearby electric power lines of overhead type or by means of a transmission line or cable adjacent and outside the theater area. The interfering signal employs the same radio frequency as is used by the induction cable in the reception area of the theater.