A filter for use in a cable television system

Claim 2

A filter for use in a cable television system for filtering out a given a portion of the frequency spectrum comprising a two pole filter, said filter including one pole which is fixed at the T.V. frequency of the portion to be removed and a second variable pole responsive to an input voltage, said second pole adapted to vary in frequency about said first pole.

Claim 3

A filter according to claim 2 wherein said second pole is tuned by means of a varactor diode.

Claim 4

Apparatus according to claim 1 or 2 and further including means for generating a periodic wave input for controlling said second pole.

Claim 5

Apparatus according to claim 3 wherein said means for generating a periodic wave include means for incorporating various frequency components into said periodic wave.

Claim 6

Apparatus according to claim 3 in combination with a cable television system and further including: a) a first single pole, double throw switch having its common terminal coupled to an incoming signal and one of its other terminals coupled to the input of said filter; and b) a second switch having its common terminal coupled to a subscriber drop, and a terminal coupled to the output of said filter, the remaining terminals of said first and second switches connected together, whereby in one position a signal will be coupled through said filter and in another position said signal will bypass said filter.

Claim 7

Apparatus according to claim 5 and further including address decoding means for decoding the address of an individual subscriber coupled to operate said first and second switches.

Claim 8

-An addressable control system for a cable television system which includes a head end from which television signals are transmitted on a plurality of channels, a plurality of receiving terminals each of which supply a group of subscribers via subscriber drops and cables interconnecting said head end with said terminals comprising: a) means at said head end for generating address and control signals for each subscriber; b) means at said head end for modulating a carrier with said address and control signal and for coupling said modulated carrier onto said cables; c) means at said receiving terminals for receiving said modulated carrier and demodulating it to recover said address and control signals; d) address decoding means for each terminal and each subscriber within a terminal coupled to decode said address and control signals; and e) means at said terminal responsive to said address decoding means and said control information to select the channels which each subscriber will receive.

Claim 9

-An addressable control system for a cable television system which includes a head end from which television signals are transmitted on a plurality of channels, a plurality of receiving terminals each of which supply a group of subscribers via subscriber drops and cables interconnecting said head end with said terminals comprising: a) means at said head end for generating address and control signals for each subscriber; b) means at said head end for modulating a carrier with said address and control signal and for coupling said modulated carrier onto said cables; c) means at said receiving terminals for receiving said modulated carrier and demodulating it to recover said address and control signals; d) address decoding means for each terminal and each subscriber within a terminal coupled to decode said address and control signals; and e) means at said terminal responsive to said address decoding means and said control information to select the channels which each subscriber will receive.

Claim 10

Apparatus according to claim 7 wherein said means to select, comprise negative traps and means to alternately switch in or bypass said negative traps.

Claim 11

Apparatus according to claim 8 wherein said negative traps comprise two poles filters having a first pole tuned to the frequency to be filtered out and a second pole which is variable in response to an input signal about said first pole and further including means at said terminal for providing a periodic wave signal to said filter trap to vary the frequency of said second pole.

Claim 12

Apparatus according to claim 9 wherein said means to supply said periodic wave is synchronized to the address and control signal frequency.

Claim 13

Apparatus according to claim 7 wherein said means for demodulating includes a local oscillator and mixer.

Claim 14

Apparatus according to claim 7 and further including means to encode the status of the received commands at said terminal and means to modulate a return carrier with said encoded states and couple said modulated return carrier onto said cable and means at said head end for receiving said modulated carrier and recovering said encoded states.

Claim 15

Apparatus according to claim 12 and further including means to compare said encoded states with corresponding command data.'

Claim 16

Apparatus according to claim 12 wherein said means for demodulating include a local oscillator and mixer and wherein said local oscillator comprises an oscillator adapted to generate an intermediary frequency for said mixer and a carrier frequency for said return signal.

Claim 17

Apparatus according to claim 14 wherein said local oscillator includes: a) a phase locked loop frequency synthesizer; b) a crystal coupled to said synthesizer; c) a voltage controlled oscillator receiving a control voltage from said synthesizer; d) a filter having long time constant disposed between said synthesizer and said voltage controlled oscillator; e) a divide by h circuit coupled to the output to said voltage controlled oscillator.