Fee-charging apparatus for television sets

Claim 1

Apparatus for use with a plurality of television receivers, each adapted to receive first television signals from non-fee-charged stations and display images in response thereto on their respective first set of channels, said first signals being received at a common antenna and each receiver having an antenna input terminal, said apparatus comprising: privately programmed transmitter means for generating second television signals from a fee-charged station having an audio portion and a video carrier signal different from the carrier signals associated with said first set of channels; coupling circuit means receiving said first and second television signals and for combining said signals and for coupling said combined signals to a common terminal; and a fee-charging unit for each receiver connected between coupling means and said antenna input terminal of an associated receiver, each unit comprising: trap circuit means receiving said combined signals from said common terminal for blocking transmission of the carrier signal of said second television signals; an oscillator circuit for generating a sinusoidal local carrier signal of substantially the same frequency and amplitude as the video carrier signal of said second television signals; band pass filter circuit means receiving the output of said oscillator circuit for rejecting harmonic signals of said local carrier signal; switch means selectively actuatable for a predetermined time in circuit with said oscillator for inhibiting said oscillator from generating said local carrier signal when actuated; and for deactivating said trap circuit means when actuated to thereby permit passage of said second television signals; and a mixer circuit receiving the output signals of said trap circuit and said filter circuit means for coupling said signals to said antenna input terminal of the associated receiver; whereby each receiver normally receives said first television signals without interference and normally receives the audio portion and mixed carrier signals of said television signals and said local carrier signal except when said switch means is actuated during which predetermined time, said oscillator circuit is inhibited from generating said local carrier signal.