CONVERTER-TUNER FOR INFORMATION TRANSMISSION SYSTEM

摘要

An individually addressable converter-tuner station for use in a cable television distribution system for selectively enabling the reception by conversion of at least one secure channel signal on a conventional television receiver. The converter-tuner utilizes a crystal-controlled local oscillator to provide the frequencies for converting the received secure channel carriers to a carrier receivable by the receiver. Initial filtration of the incoming secure channel carriers is accomplished in part by means of a tunable pass band filter, controlled by a variable capacitance diodes. A double balanced mixer is employed to cancel unwanted signals remaining in the filtered input to the mixer. The secure channel carriers are in the television midband range, and the local oscillator frequencies are below that range. Extensive use is made of diode switching of the crystal controlled oscillator and other components.