SELECTIVE INTERDICTION OF TELEVISION CHANNELS

Abstract: With the present decoder/interdiction device combination (566), the microcontroller (518) receives authorization data from a data receiver (568) via its data output (570) that has been inserted at the headend to identify authorized subscribers (preferably identified with a predefined subscriber or box code in the microcontroller (518). The same microcontroller (518) that controls the common decrypting of a commonly encrypted input source (572), loads the channel interdiction table (516) according to the authorization data, e.g., according to tiers. The data in the interdiction table (516) is then used to control the operation of the frequency synthesizer/VCO (516) and the mute switch (522) using the control interface (528) and mute control signal (534) according to the previously described algorithm. This improved combination now permits the simultaneous reception of multiple unencrypted signals (suitable for picture-in-picture use) while still permitting the provider to withhold access to selected channels.

Description: Selective Interdiction of Television Channels BACKGROUND OF THE INVENTION The present invention relates generally to multichannel television systems and more particularly to interdiction devices for selectively scrambling television channels at subscriber sites. Subscription television distribution systems (either (1) cable or (2) over-the-air) typically provide a basic block of television channels to subscribers at a subscriber site for a basic monthly fee and one or more premium television channels for additional fees. In a typical cable system, the physical connection itself controls access to the basic channelε while premium channels are often "scrambled" (encrypted) at their source, i.e., the headend, by the provider to restrict their viewing to only subscribers who pay the additional fee. Alternatively, providers may provide unscrambled (in-the-clear) channels to each subscriber site where the provider physically places an interdiction device which blocks, e.g., attenuates or scrambles, selected channels to stop unauthorized subscribers from receiving the selected channels. In over-the-air subscriber systems (often called "wireless cable or TV"), all channels are generally scrambled at the headend to prevent unauthorized reception of both basic and premium channels since the transmitted channels are available to anyone in the geographical service area. Subscribers are typically provided with a descrambler (decoder) which can descramble (decode/decrypt) only one channel at a time. Therefore, subscriber receivers, e.g., television sets, videocassette recorders, can only be tuned to a single selected channel and features of modern television equipment that process multiple channels, e.g., "picture-in-picture", are useless. // // // // // 1 SUBSTITUTE SHEETS SUMMARY OF THE INVENTION The present invention is directed to a decryption process which facilitates simultaneous decryption of a block of encrypted television channels thus making a decrypted block of television channels simultaneously available for direct tuning by subscriber receivers. Additionally, the present invention is directed to an encryption process which facilitates the jamming of selected television channels from said decrypted block thus making it possible to interdict reception of those selected channels by unauthorized subscribers. The present invention can be advantageously used in both over-the-air and hard-wired subscription television distribution systems to provide subscribers with a plurality of simultaneously available decrypted television channels and selectively encrypted channels, e.g., premium channels. A system in accordance with the present invention is characterized by a selective interdiction device located at a subscriber site that operates on a block of television channels, decrypted at the subscriber site, such that the interdiction device jams one or more selected channels, e.g., premium, by combining a jamming signal within the frequency range of the channels to be interdicted. A preferred subscriber site apparatus useful in a system for distributing from a system headend 1 ) multiple channel signals defining an RF band, each channel signal having respective video synchronization components in time coincidence and 2) a common timing reference signal within said band and synchronous with said synchronization components, and wherein each of said channel signals is encrypted in accordance with a common encoding rule comprises a) a timing recovery circuit responsive to said common timing reference signal for generating at least one sync signal, b) a single decoder responsive to said sync signal for simultaneously decrypting all of said channel signals in accordance with the inverse of said encoding rule to generate multiple decrypted channel signals, each capable of directly causing a conventional television receiver to produce an intelligible image, and c) an interdiction apparatus for periodically inserting a jamming signal into at least one of said multiple decrypted channel signals to render it incapable of directly causing said television receiver to produce an intelligible image. Alternatively, a preferred subscriber site apparatus useful in a system for distributing from a system headend 1) multiple channel signals defining an RF band, each channel signal having respective video synchronization components in time coincidence and 2) a common timing reference signal within said band and synchronous with said synchronization components, and wherein each of said channel signals is encrypted in accordance with a common encoding rule comprises a) an interdiction apparatuε for periodically inserting a jamming signal into said RF band to generate an interdicted RF signal, b) a timing recovery circuit responsive to said common timing reference signal for generating at least one sync signal and c) a single decoder responsive to said sync signal and said interdicted RF signal to simultaneously decrypt multiple channel signals in accordance with the inverse of said encoding rule to generate a recovered multichannel signal comprising multiple decrypted channel signals capable of directly causing a conventional television receiver to produce an intelligible image and at least one scrambled channel signal incapable of directly causing said television receiver to produce an intelligible image. The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. // // // // // // // // // // // // BRIEF DESCRIPTION OF THE DRAWINGS Figure IA illustrates that decryption is typically restricted to a single selected channel signal in prior art subscription television distribution systems,- Figure IB illustrates that decryption provides simultaneous access to all encrypted channel signals in a subscription television distribution system in accordance with the present invention,- Figure 2 illustrates encryption/decryption processes in accordance with the present invention,- Figureε 3A and 3B are block diagrams of alternative embodiments of an encryption system configured to facilitate the simultaneous decryption of all encrypted channel signals; Figure 4 is a block diagram of apparatus for simultaneous decryption of channel signals generated by the systemε of Figures 3A and 3B; Figure 5 illustrates a typical composite video signal; Figure 6A is an enlarged view of the picture and horizontal synchronization components of a plurality of composite video signals,- Figure 6B illustrates the composite video signals of Figure 6A with like components in time coincidence,- Figure 6C illustrates an exemplary encoding rule for encoding the components of the composite video signals of Figure 6B; Figure 6D illustrates a plurality of encoded composite video signals resulting from modification of the composite video εignals of Figure 6B in accordance with the encoding rule of Figure 6C; Figure 6E illustrates a plurality of video IF carriers, each amplitude modulated with a different one of the encoded composite video signalε of Figure 6D; Figure 6F illustrates a decoding rule which is the inverse of the encoding rule of Figure 6C; Figure 6G illustrates the video IF carriers of Figure 6E after modification in accordance with the decoding rule of Figure 6F; Figure 7 illustrates the command transmiεεion εtructure comprised of multiple data bytes and a reference pulse that are added to a selected channel signal; Figure 8 illuεtrateε the relationεhip of the command transmission structure of Figure 7 to a typical 525 line, 60 HZ television signal; Figure 9 illuεtrateε the relationεhip of the reference pulεe to the tenth horizontal εync pulse in the televiεion signal of Figure 8; Figure 10 illustrates the relationship of the command tranεmission structure of Figure 7 to a typical 625 line, 50 Hz television signal; Figure 11 illustrates the relationship of the reference pulse to the eighth horizontal εync pulse in the televiεion εignal of Figure 10; Figure 12 is an expanded block diagram of a portion of the procesεing of video channel N as shown in Figure 3B; Figure 13 is a top level block diagram of an up/down converter embodiment of the data modulator of Figures 3B and 12 ; Figure 14 is a detailed block diagram of a preferred up/down converter as shown in Figure 13 ,- Figure 15 iε a block diagram of a preferred embodiment of the decoder portion of the downconverter/decoder aε shown in Figure 4; Figure 16 is a detailed block diagram of an exemplary embodiment of the decoder of Figure 15 ,- Figure 17 is a simplified block diagram showing the use of a selective multichannel interdiction device of the preεent invention that εelectively jams predetermined premium channels,- Figure 18 iε a block diagram of a preferred selective multichannel interdiction device that jams predetermined premium channels by adding a jamming εignal to each of the εelected premium channel εignalε; Figure 19 εhowε an exemplary flow chart for a controller that controlε the combining of a jamming signal with the multichannel television signal; and Figure 20 iε a block diagram of a preferred embodiment of the present invention combining a selective interdiction device with a decoder. // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // DESCRIPTION OF THE PREFERRED EMBODIMENTS Aε εhown in Figure IA, typical prior art televiεion diεtribution systems provide subεcribers with a plurality of encrypted television channel signals 20 but restrict decryption 22 to the production of one decrypted channel signal 24 at a time. Thus, for example, a εubεcriber can cauεe any one of the encrypted channel signals 20 to be decrypted for viewing on a television set but cannot at the same time record another decrypted channel signal on a video cassette recorder or use another channel signal for a "picture-in-picture" system. In an attempt to address this limitation, one prior art syεtem useε a plurality of decoderε, e.g., 22A-22N, one for each encrypted channel signal, that respectively decode the channel signalε which are then upconverted by a plurality of upconverterε 25A-25N to a new channel frequency 26A-26N. Figure IB illustrates that encryption/decryption syεtemε taught by the preεent invention facilitate decryption 28 of all encrypted channel signals 30 simultaneouεly εo that a complete set of decrypted channel signalε 32 iε εimultaneously available in their original frequency slots. Therefore, a subscriber can have each of a plurality of subscriber receivers (e.g., television setε, video cassette recorders) receiving a different channel signal εimultaneouεly while alεo uεing modern televiεion processing features, e.g., picture-in-picture, which require simultaneous availability of multiple channel signalε. An encryption/decryption procesε 40, in accordance with the invention, iε shown in Figure 2. Television distribution systems typically include a "headend" where a plurality of television channel signalε from different sources, e.g., satellite TV signals, standard broadcast VHF and UHF signalε, are captured, combined and fed into the εyεtem. In the procesε 40, headend generation 42 of multichannel televiεion εignalε beginε with a plurality of video sources 44 which each provide a composite video signal 45 including picture and synchronization components (as εhown in Figure 5 and further described below) . The composite video signalε 45 are encrypted 50 and used to modulate 52 separate channels to place them into separate frequency channels for distribution. In addition, a process of time synchronization 54 is imposed to place like components of the compoεite video εignalε 45 in a predetermined time relationεhip. Diεtribution 60 to εubscriber sites 66 of the channel signalε generated at the headend may then be accomplished by a variety of well known procesεeε, e.g., cable tranεmission or wirelesε over-the-air transmission, as a common RF signal 68 that contains each composite video signal in a distinct frequency slot. Because of the time synchronization 54 imposed at the headend, the common RF signal 68, comprised of a plurality of television channel signals separated in frequency, arrive at the subscriber siteε 66 in time synchronization so that decryption 70 can be performed on all channel signals simultaneouεly. Apparatus embodiments for realizing the processes of Figure 2 are illustrated in Figures 3A, 3B and 4. Figure 3A showε a block diagram of a headend 100 in which baseband composite video sourceε 102A-102N are each connected to εeparate electronic delay deviceε εuch aε frame εynchronizers 104. The frame εynchronizers 104 selectively delay the composite video signals from the sources 102A-102N to place like components, e.g., picture and synchronization components, in time synchronization with reference to a crystal controlled video reference 105, thus generating time synchronized composite video signalε 106. The crystal controlled video reference 105 is coupled to a timing reference generator 108 used to synchronouεly generate a common timing reference εignal 109, as described further below. The time synchronized composite video signals 106 are used to amplitude modulate separate video IF carriers in IF modulators 110 after which encryption iε accompliεhed by modifying IF envelopes in accordance with a selected encoding rule (code) in encoders 112, thus generating encoded IF carriers 113. Typical apparatus for envelope modification include variable gain amplifiers, variable loss attenuators and selectable signal pathε having different gainε. Exemplary envelope modification apparatus are disclosed in U.S. Patents 4,706,283; 4,802,214; 4,926,477; and 4,928,309, the disclosures of which are hereby incorporated by reference. The modulators 110 and encoders 112 of Figure 3A may alternatively be interchanged, as shown in Figure 3B, to use the encoder 112 to first encode the time synchronized video signals 106 by amplitude modification in accordance with a selected encoding rule and then using the resultant signal to amplitude modulate an IF carrier with the IF modulator 110. Video amplitudes may be modified with apparatus similar to the above mentioned examples . Specific apparatus for video baseband envelope modification is diεclosed in U.S. Patent 4,928,309, the discloεure of which is hereby incorporated by reference. The encoded IF carriers 113 are preferably upconverted from a standard IF frequency and frequency multiplexed in standard television transmitterε 114 for diεtribution to εubεcriber εiteε aε the common RF εignal 68. The RF frequency εlotε are typically εpecified in accordance with industry standardε . For example, a typical Multichannel Multipoint Diεtribution Service (MMDS) includeε 33 channel εlotε within a transmission frequency range of 2500-2686 MHz and 2150- 2162 MHz. The timing reference generator 108 generates the common timing reference signal 109 which is transmitted with the synchronized video signalε to provide master timing information for decoding synchronization. This signal is preferably combined with a selected encoded IF carrier 113 to form a data modulated IF carrier 115, by a data modulator 116. The data modulator 116 is placed in a selected channel at the headend but it may alternatively be inserted (indicated by broken line) into a transmitter 117 to be carried by an otherwise unused RF channel 118. The data modulator 116 may alternatively be present on more than one of the video channels prior to the transmitters 114 and selectively enabled at the headend. Authorization data statuε (deεcribed further below) iε alεo preferably combined with the common timing reference εignal 109 and transmitted to selectively enable or disable decoding at each subεcriber εite. Figure 4 illustrates a block diagram of a downconverter/decoder 120 suitable for simultaneous decryption at subscriber sites of the common RF signal 68 received from the headend 100 of Figures 3A and 3B. In the block diagram of Figure 4, downconverεion electronicε 121 are shown essentially comprised of an input RF amplifier 122, a mixer 123 and a local oscillator 124. The input RF amplifier 122 amplifies and buffers the common RF signal 68 that was alternatively broadcast or distributed via cable from the transmitters 114 of Figures 3A and 3B. The amplifier 122 feeds a buffered common RF signal 126 to the mixer 123 which downconverts the buffered common RF signal 126 using the local oεcillator 124, generating a downconverted common RF εignal 126. In a preferred embodiment, the common RF εignal 68 iε received via a microwave antenna (not εhown) and εubεequently downconverted via the downconverεion electronicε 121 aε diεclosed in U.S. Patent No. 5,440,319 to Joel J. Raymond et al. , which is incorporated herein by reference. From the downconverted common RF εignal 126, the common timing reference εignal (109 in Figureε 3A and 3B) iε recovered in a data/timing receiver 127. Thiε receiver 127 alεo εtores a decoding rule which is the inverse of the selected encoding rule used in the encoders 112 of Figures 3A and 3B. Specific structure in the receiver 127 for recovery of the common timing reference signal 109 is primarily dependent upon the type of timing signal selected. Exemplary recovery structureε are diεcloεed in U.S. Patentε 4,706,283; 4,802,214; 4,926,477; and 4,928,309, previouεly referred to above and incorporated herein. With the common timing reference εignal and the decoding rule available (and preferably after confirmation of the authorization data) , the data/timing receiver 127 can apply gain control εignalε 128 to a variable gain amplifier/attenuator 130 which εimultaneously modifies the IF carrier envelopes with signal 126 in accordance with the decoding rule to generate decoded channel signals 132. In a preferred embodiment, the variable gain amplifier/attenuator 130 is a single element that operates on a single multichannel television signal derived from the common RF signal 68. It is this ability to operate upon all television channel signals by a single element that is referred to in this application as "simultaneous". While a preferred embodiment useε a εingle variable gain amplifier/attenuator 130, other embodimentε may uεe additional variable gain/amplifiers to synchronously operate upon a multichannel signal derived from the common RF εignal 68 in an equivalent manner. Thuε, the decoded channelε 132 are now εimultaneouεly available and can be distributed throughout the subεcriber site for delivery to multiple subεcriber receiverε without further proceεεing. In addition, once the data/timing receiver 127 preferably confirmε the authorization data, all channelε will automatically be available for use, i.e., no user interaction, such aε εelecting a channel for decoding, will be involved. The downconverter/decoder 120 of Figure 4 can be economically integrated to reduce εubscriber coεts. The invention is further disclosed by a preferred procesε embodiment illustrated in Figures 6A-6G. Description of this exemplary embodiment is facilitated by reference to a typical compoεite televiεion video εignal 220, εhown in Figure 5, as specified by television industry standards, e.g., National Television Systems Committee (NTSC) . The signal 220 of Figure 5 has picture components 222 alternating with horizontal εynchronization componentε 224 and theεe componentε are periodically εeparated by vertical εynchronization componentε 226 during a vertical synchronization interval. The vertical synchronization components 226 generally include equalizing pulεeε 230, vertical synchronization pulses 232 and horizontal synchronization pulseε 234. Aε iε well known, the horizontal εynchronization components 224 and vertical synchronization components 226 enable televiεion receivers to properly synchronize the picture display. Figure 6A is an enlarged view of the picture components 222 and horizontal synchronization components 224 of a plurality of compoεite video εignalε 220A-220N. Each horizontal εynchronization component 224 is seen to include a horizontal synchronization pulse 242 and, as in the case of color television, a color burεt εine wave 244 (indicated by the sine wave envelope) . In this preferred method, like components of the video signalε 220 are first aligned in time coincidence as shown in Figure 6B and their amplitude then modified in accordance with a εelected encoding rule. To illuεtrate this amplitude modification, an exemplary encoding rule, having an encoding pattern 250 of Figure 6C, will be used. The pattern 250 is visually indicated by two lines 251 equally vertically spaced about a centerline 252 in which the vertical spacing between lineε 251 indicateε gain. Thuε, the pattern 250 haε εegmentε 253 with a gain 254 interleaved with εegmentε 255 having a decreased gain 256. The encoding pattern 250 is synchronized with the composite video εignalε 220A-220N of Figure 6B to have gain εegmentε 253 and gain εegmentε 255 time coincident reεpectively with picture componentε 222 and horizontal εynchronization componentε 224. The pattern 250 and the particular time εynchronization deεcribed above are for illuεtrative purpoεes only; any encoding rule and time synchronization may be used that will prevent unauthorized television receivers from properly displaying the video signal. When the amplitudes of the video signalε 220A-220N are modified in accordance with the encoding pattern 250, a plurality of encoded video εignals 260A-260N is produced having picture components 222' and horizontal synchronization components 224' as shown in Figure 6D. Synchronism between one of the gain segmentε 255 and a correεponding horizontal εynchronization component 224" iε indicated by the broken lineε 266. Thuε, in the encoded compoεite video εignalε 260A-260N, the horizontal εynchronization componentε 224 are reduced relative to the other video componentε. In Figure 6E, a plurality of video IF (intermediate frequency) carrierε 270A-270N have each been amplitude modulated with a different one of the encoded video εignals 260A-260N to have amplitude envelopes 271A-271N as shown in broken lineε. The modulated video IF carrierε thuε have portionε corresponding to the components of the encoded composite video signals 260 of Figure 6D, e.g., picture portions 272 and horizontal synchronization portions 274 correspond respectively to picture components 222' and horizontal synchronization components 224' . In the preferred method, upon receipt at a subscriber site, the video IF carriers 270A-270N are εimultaneously shaped in accordance with the inverεe of the encoding pattern 250. Figure 6F illustrates this inverse aε the decoding pattern 278 in which the gains 254, 256 have been inverted, i.e., segments 255 now have the increased gain 254 while segmentε 253 have the decreased gain 256. The decoding pattern 278 is synchronized with the modulated video IF carriers 270 of Figure 6E in the same manner as was done with the encoding pattern 250 of Figure 6C and the composite video signalε 220 of Figure 6B, i.e., gain εegmentε 253 and gain εegments 255 are made time coincident respectively with picture portionε 272 and horizontal εynchronization componentε 274. Aε shown in Figure 6B, when the amplitudes 271A-271N of Figure 6E are modified in accordance with the decoding pattern 278, a plurality of video IF carriers 280A-280N, with amplitude envelopes 281A-281N, are produced each having picture portions 272 and horizontal synchronization portions 274 which conform respectively with the picture components 222 and horizontal synchronization components 224 of Figure 6B. Synchronism between one of the gain segments 255 and a corresponding horizontal synchronization portion 274' is indicated by the broken lines 288. Thuε, all video IF carrier εignals have been simultaneously decoded at the subscriber site without any change in frequency allocation and are simultaneously available for uεe. In Figureε 6C, 6D and Figureε 6F, 6G, the εynchroniεm between the inverεe decoding rule 280 and video IF portions 272, 274 was specified to be the same as between the encoding rule 250 and corresponding video components 222, 224. As previously discussed, this synchroniεm iε realized with a common timing reference εignal εynchronouε with the encoding which iε then recovered at the εubεcriber εite for εynchronizing the decoding of the encoded channel εignals. Typical modulation methods for carrying timing reference signalε on IF or RF carriers include amplitude modulation, frequency εhift keying and phaεe shift keying. A preferred embodiment employing frequency shift keying is described further below. The common timing reference signal may preferably be inserted in synchronization components, i.e., horizontal or vertical, to avoid disturbing picture information. The common timing reference signal is preferably combined with authorization data which is coded into one or more video IF carrier signals. In the preferred method embodiment illustrated in Figures 6A-6G, generation of the video carriers with encoded amplitudeε 271A-271N, as shown in Figure 6E, followed the sequence of video signal time alignment, amplitude modification of video signals in accordance with a selected encoding rule and modulation of video IF carriers with the encoded video εignals. It should be apparent, however, that other method embodiments, in accordance with the invention, may employ other equivalent sequenceε, e.g., the sequence previouεly deεcribed and εhown in Figureε 3A and 3B. Alεo, the illuεtrated preferred method embodiment εimultaneously decodes modulated IF carriers. It should be apparent to those skilled in the art that equivalent method embodiments may include transmiεεion techniques such as the upconverεion of each IF carrier to one of a plurality of RF frequency εignalε followed by frequency multiplexing. The reεulting RF frequency εignals may then be modified in accordance with the inverse of the selected encoding rule to simultaneouεly decode the video εignalε carried therein. Both IF and RF εignalε may be generically referred to aε channel εignalε. Although the encryption/decryption process shown in the preferred embodiments has been specifically directed to amplitude modification of analog video signalε, the teachingε of the invention may generally be extended to encryption/decryption of other forms of video signals, e.g., bit streamε reεulting from digitization of analog video εignalε. Also, although horizontal sync suppression has been shown aε an encoding method, other encoding methodε are also recognized within the scope of the present invention, including vertical sync εuppreεεion and horizontal and vertical εync εuppression. In addition, the illustrated preferred method embodiment aligned corresponding video components in time coincidence for simultaneouε decryption at εubεcriber sites but other embodiments of the invention may synchronize (i.e., place in a predetermined time sequence) corresponding video components for synchronouε decryption at εubscriber εiteε. With reference now to Figure 7, there is shown a diagram of a preferred command transmission structure of the data that is added to a selected television channel for providing εynchronization and the authorization data. The basic structure of the authorization data is preferably comprised of twelve data bytes, divided into two data blocks 300 and 302 of six bytes each, correεponding to the two interlaced fieldε which form a εingle video frame and a preciεely placed reference pulse 304 used to provide timing information for decrypting the common RF signal 68. Additionally, start sequences 306 and 308 are provided to identify the start of each data block. The data bytes are preferably used to identify authorized individuals or groups of authorized subscribers to the otherwise encrypted service. At leaεt one byte iε preferably included aε a validity check byte 310 for the authorization data. Additionally, the validity check byte 310 may be used to determine valid receive timing synchronization. In a typical 525 line, 60 Hz television signal, as shown in Figure 8, a video frame is comprised of 525 interlaced horizontal lines of video information divided into two fields at a 30 Hz frame rate. The beginning of each field is signified by vertical sync components 312 and 314, defining a vertical synchronization interval, that cause a vertical retrace during which the screen is blanked. Video information need not be present during the vertical synchronization interval since the screen is blanked. Thus, as shown in Figure 8, a preferred embodiment useε the vertical εynchronization interval, defined by vertical sync components 312 and 314 and comprised of multiple horizontal lines, to transmit the authorization data without interfering with the displayable video information. Transmisεion of the firεt data block 300, comprised of the first start sequence 306, a first set of data bytes 318, six data bytes in a preferred embodiment, and the reference pulse 304, begins with the time period defined by the first horizontal line 316. While the data transmisεion protocol iε otherwiεe tolerant to timing variationε, the reference pulεe 304 iε preciεely εynchronized with a horizontal εync pulεe 320 that followε the tenth horizontal line 322. The transmission period for the first data block 300 is contained within the time period for horizontal lineε 1-10, aε εhown in Figure 8. Similarly, the tranεmission period of the second data block 302, compriεed of the εecond start sequence 308 and a second set of data bytes 324, six data bytes in a preferred embodiment, is contained within horizontal lines 263-272. Using meanε diεcuεεed below, data iε modulated onto a selected televiεion channel during the previouεly deεcribed vertical εynchronization interval. Aε shown in Figureε 7, 8 and 9, thiε data is defined as a combination of bits comprised of marks, i.e., "l"s or "high"s, and spaceε, i.e., "0"ε or "low"ε. However, outεide of theεe preεcribed periodε, data values are undefined and potentially susceptible to erroneous detection as marks or spaces. To avoid these errorε, the start sequences 306 and 308 are used in combination with the validity check byte 310 to define detection periods corresponding to horizontal lines 1-10 and 263-272. The start sequenceε 306, 308 are each defined by a serieε of unique data bits, all "l"s in a preferred embodiment. Each data byte within the firεt and εecond εets of data bytes, respectively 318 and 324, are preferably transmitted as 8-bit characters according to a conventional 11-bit asynchronouε protocol, aε shown in Figure 9, with one low εtart bit 325 and two high εtop bitε 326 per character. Aε iε common with aεynchronouε character tranεmission protocols, the time each character is transmitted is not precisely fixed in time. However, a transmission rate is chosen that permits the transmisεion of an 11-bit start sequence 306, six 11-bit characters 318 and εtill provide εufficient time to preciεely place the reference pulεe 304 in εynchronization with the horizontal sync pulse 320 following the tenth horizontal line 322. In a preferred embodiment, a bit rate of 140,625 bps is used. While, the reference pulse 304 is deεcribed here in reference to a particular video signal, e.g., 220B, it should be recognized that since all of the video signalε 220A-220N are synchronized by frame synchronizers 104, the reference pulse 304 will be precisely synchronized to the horizontal sync pulse following the tenth line for all of the video signals. With reference to Figures 10 and 11, there is εhown the interrelationεhipε of the video information and the authorization data for a televiεion εignal which uεes 625 lines at a 25 Hz frame rate to represent each video frame. In such a television signal, as shown in Figure 10, a first data block 327 is placed within horizontal lines 624 and 9 and a second data block 328 is placed within horizontal lines 311 and 320. The reference pulse 330 is precisely placed in synchronization with the horizontal sync pulse following the eighth line 332. In a preferred embodiment, the television channel εelected for transmitting the authorization data is fixed, e.g., always set to a predetermined channel N. However, the downconverter/decoder 120 is preferably configured to scan channels within its frequency range to identify the channel containing the authorization data. Alternate embodiments may alter the data channel selection according to a predetermined algorithm, e.g., a different channel for each time period, a first data channel identifies a next data channel, etc. As discuεεed in reference to Figureε 3A and 3B, the common timing reference signal 109 can alternatively be coupled to any one or all of a plurality of data modulators 116. A εelect εignal (not εhown) can optionally enable a particular data modulator 116 to add the common timing reference εignal 109 to a selected channel. With reference now to Figure 12, there is shown an expanded block diagram of a portion of the encryption procesεing of video channel N, as shown in Figure 3B, showing the interface of the encoder 112N and the IF modulator 110N to the data modulator 116. In a preferred embodiment, the encoder 112N applieε a εelected encoding rule, e.g., removing the horizontal and vertical εynchronizing componentε 224, 226 from a time εynchronized video εignal 106N, to diεable subscribers without authorized decoders from receiving a video channel. An encrypted video signal 334 is then modulated by the IF modulator 110N, generating the encoded IF carrier 113N. In a preferred embodiment, the encoded IF carrier 113N from the IF modulator 110N is modulated by the data modulator 116 during the time period corresponding to the vertical synchronizing component 226, i.e., the vertical synchronization interval, in responεe to the common timing reference signal 109 and sent via the data modulated IF carrier 115 to the transmitter 100N. As described above, the data modulator 116 is only present on a selected channel 1-N in a preferred embodiment. In another embodiment, the data modulator 116 may be present for all N channels but may be enabled only for the selected channel or alternatively for a plurality of channels. Alternatively, a single data modulator 116 may be switched to the selected channel. The timing reference generator 108, under control of a microcontroller 340, generates the common timing reference signal 109 in synchronism with a clock 342 received from the crystal controlled video reference 105. As previously diεcuεεed, the common timing reference εignal 109 additionally preferably compriεeε the authorization data for specifying authorized subscriber . Authorization information iε maintained in a system controller (not shown) and communicated via signal path 344 to the microcontroller 340 where it is formatted aε the authorization data onto the common timing reference εignal 109. In a preferred embodiment, the common timing reference εignal 109 containε three data εtateε correεponding to no data, a mark and a space, thus causing the data modulator 116 to alter the encrypted IF signal 113 on receipt of a mark or space but leave the encrypted IF signal 113 unaltered when receiving a third, no data, state signal. Alternatively, the cryεtal controlled video reference 105 deliverε a sync signal 346 to the data modulator 116 to enable data modulation only during the vertical synchronization interval. In a preferred embodiment, the data modulator 116 uεeε FSK (frequency εhift keying) to modulate the encoded IF carrier 113 of a εelected MMDS channel with the authorization data and the reference pulεe 304 during the vertical εynchronization interval. The encoded IF carrier 113, aε input to the data modulator 116, iε either εeparate video and εeparate audio modulated IF carrierε, or the combined video and audio modulated carrierε. In addition, the data modulator 116 receiveε the common timing reference εignal 109, compriεed of the reference pulεe 304 and the authorization data comprised of setε of data byteε 318 and 324 uεed to authorize or deauthorize each εubscriber. The outputs of the data modulator 116 are the audio and video carriers, FM modulated with the setε of data byteε 318 and 324 and the reference pulεe 304 during the vertical εynchronization interval. The preferred data modulator 116 is characterized by: 1) the difference between the output frequencies of the modulated carriers are the same as their respective input carrier frequencies, 2) the syεtem should not add noise or distortion to the modulated carriers, and 3) the audio and video carriers should match in deviation and phase. Since the audio carrier is typically produced as a beat frequency between the audio and video IF carriers, if the audio and video IF carriers do not match in phase and maintain the frequency difference of the original carriers, an unwanted hum could be produced. With reference now to Figure 13, there is shown a top level block diagram of an up/down converter embodiment 348 of the data modulator 116. In this embodiment, the encoded IF carrier 113 is comprised of a separate video IF carrier 350 and audio IF carrier 352. In an exemplary embodiment, the video IF carrier 350 and the audio IF carrier 352 are typically at 45.75 MHz and 41.25 MHz, respectively, and are nominally separated in frequency by 4.5 MHz. The reference IF carrier 353, generated by the up/down converter 348, is comprised of a separate video carrier+data signal 354 and audio carrier+data signal 356, both of which are uniformly FSK modulated in responεe to the common timing reference signal 109. In a preferred embodiment, the data responεive frequency deviation for the carrierε 350 and 352 is ±25 KHz. In Figure 14, a detailed block diagram of a preferred up/down converter 348 is shown. The up/down converter 348 conεists of a two pairs of mixers 358, 360 and 362, 364, one pair for each carrier, i.e., video 350 and audio 352, under control of a common pair of local oscillators. First and second oscillatorε 366 and 368 are VCOε (voltage-controlled oεcillatorε) phaεe locked to a common cryεtal oεcillator 370. The firεt oεcillator 366 functionε as a local oscillator (LO) 372 to mix each carrier up to an intermediate frequency and the second oscillator 368 functionε aε a εecond local oscillator 374 to mix the signal back down to itε original IF frequency. In the procesε of downconversion, the second local oscillator 374 is frequency modulated with the data from the common timing reference signal 109. Since the second local oscillator 374 changes frequency in response to the common timing reference signal 109, the downconverted carriers 354 and 356 alεo change frequency and additionally contain FSK data providing εynchronization and the authorization data. The second local oscillator 374 used for the second downconversion is frequency modulated as follows. The phase locked loop of the VCO 368 is used in the second downconversion. The common timing reference signal 109 is summed onto a control line 376 of this VCO 368. Since the modulated VCO 368 is used aε the local oεcillator 374 for the downconverεion, the RF carriers 354 and 356 are also modulated and thus contain the FSK data. In Figure 14, the audio and video carriers are separate and thus, this same process is performed in parallel on both the video and audio carriers 350 and 352 using the εame two local oεcillators 372 and 374. Signals from each oscillator 372, 374 are split and respectively sent to two mixers 358, 362 and 360, 364. The audio carrier 352 is upconverted uεing the first local oscillator 372 and then downconverted to the original IF frequency using the FM modulated second local oscillator 374. Since the same frequency modulated local oscillator 374 is used in the downconversion of the audio and video carriers, the frequency deviation of both carriers will be esεentially identical. With reference now to Figure 15, there iε εhown a preferred embodiment of a decoder portion 400 of the downconverter/decoder 120, aε deεcribed in reference to Figure 4. Aε previously described, the decoder portion 400 receiveε the downconverted common RF εignal 126, recoverε the common timing reference εignal 109 contained within uεing the data/timing receiver 127, and in response generates gain control signals 128 to instruct the gain amplifier/attenuator 130 to operate upon the downconverted common RF signal 126 according to the inverse of the selected encoding rule, e.g., reinserting horizontal and vertical components, to generate the decoded channelε signal 132. The decoded channels signal 132 can be distributed to one or more standard television receivers which can independently receive one or more decoded television channels. The data/timing receiver 127 is preferably comprised of a superheterodyne dual conversion FSK data receiver 402 under control of a controller 404. The controller 404, receives a decoded data output signal 406 from the data receiver 402 and generates frequency control signalε to phaεe lock the data receiver 402 to the decoded data output signal 406. Additionally, the data/timing/receiver 127 preferably compriseε an input attenuator 408 that acceptε the downconverted common RF signal 126 and, under control of the controller 404, generateε a common attenuated signal 410 to the data receiver 402 and the gain amplifier/attenuator 130. The controller 404 additionally receives a receive signal εtrength indicator (RSSI) 412 from the data receiver 402 and responsively generates an attenuation control signal 414 to the input attenuator 408. The controller additionally generates gain control signalε 128 to the gain amplifier/attenuator 130 compriεed of a blanking control line 416 and a εync control line 418. Theεe control lines are used for reinserting the vertical and horizontal sync signals, respectively, into the common attenuated signal 410 derived from the downconverted common RF signal 126. The data receiver's 402 principal purpose is to retrieve the common timing reference signal 109 from a selected channel within the common attenuated signal 410 and to deliver the common timing reference signal 109 as the decoded data output signal 406, representative of the authorization data and the precisely timed reference pulse 304. The data receiver 402 is comprised of a first IF 420, a second IF 422 and a data detector 424. The first IF 420, receives the common attenuated signal 410, typically having a frequency range of 222 to 408 MHz corresponding to CATV channels 24 to 54, and downconverts the εelected channel to a fixed frequency first IF output signal 426. The εecond IF 422 then further downconvertε the firεt IF output εignal 426 to a fixed frequency εecond IF output εignal 428. The second IF output signal 428 iε input to the data detector 424 which extractε the decoded data output signal 406 and the receive signal strength indicator 412. The channel selection is determined by the controller 404 by εcanning the available channels for data. To scan the available channels, the controller 404 generateε a channel select signal 430 to the first IF 420 which determines the amount of frequency downconversion required for the common attenuated signal 410. The channel select signal 430 is iteratively altered until data is succeεεfully received. Additionally, the controller 404 generateε a second IF frequency select signal 432 to the second IF 422. In a preferred embodiment, the operating frequencies of the first IF 420 and the second IF 422, as determined by the channel select 430 and second IF frequency select 432 signals are adjusted by the controller 404 in responεe to the decoded data output signal 406, thus phase locking the data receiver 402 to the data contained within, i.e., the common timing reference signal 109. Figure 16 showε a detailed block diagram of an exemplary embodiment of the decoder 400 of Figure 15, comprised of the first IF 420, the second IF 422 and the data detector 424, that εendε data to the controller 404 that in turn controls the gain amplifier/attenuator 130, comprised of two switchable RF attenuatorε, to re-inεert εync and blanking signals directly on cable television frequencies. In a preferred embodiment, video channels contained within the downconverted common RF signal 126 do not contain horizontal or vertical sync pulses. In addition, the horizontal blanking level corresponding to each channel within the common RF signal 68 is preferably attenuated to prevent detection circuitry of some television receivers from using the blanking signal as a false sync reference. During the vertical synchronization interval, the blanking level is not attenuated by the encryption. The decoder 400 performε the inverse of the selected encoding rule to restore the sync and blank signals to proper levels using a pair of two level RF attenuatorε, a blanking εwitch 434 and a sync switch 436. An amplifier 438 isolateε the blanking and εync switches 434, 436 to prevent signal interactions. The amplifier 438 is preferably a linear amplifier capable of handling multiple high level carriers with low distortion. A pad 440 helps to isolate the εync εwitch 436 from poor external impedance matching. The input attenuator 408 is activated when the downconverted common RF signal 126 reaches a certain level. This prevents distortion of both the gain amplifier/attenuator 130 and the data/timing receiver 127. The receive signal strength indicator 412, generated by the data detector 424, provides information for the controller 404 to determine at what level to εwitch in the input attenuator 408 via the attenuator control εignal 414. A resistive splitter 442 provides a signal to both the gain amplifier/attenuator 130 and the firεt IF 420. The reεiεtive splitter 442 also helpε to iεolate and prevent interaction with the input attenuator 408. The data receiver front end includeε a high iεolation amplifier 444 to iεolate a firεt local oεcillator 446. A pad 448 at the input of the amplifier 444 preventε diεtortion of the amplifier 444 from the multiple carrierε within the downconverted common RF signal 126. A pad 450 at the output of the amplifier 444 provides an eaεy broadband match to the input of a firεt mixer 452 and also preventε distortion. Both attenuators 448 and 450 also help iεolate the first local oscillator 446. The first mixer 452 and the first local oscillator 446 combination provide a programmable local oscillator frequency range. The data carrier can be any of the video carriers in this band. The IF frequency is preferably chosen to avoid mixing of carriers within the frequency range. A frequency synthesizer 454 keeps the first local oscillator 446 in phase lock while receiving a reference frequency from the controller 404. The frequency syntheεizer 454 is preferably capable of tuning the first local oscillator 446 using the channel select signal 430 from the controller 404. In a preferred embodiment, the controller 404 iteratively tunes the first local oεcillator 446 until data iε εucceεsfully received. Alternatively, the controller 404 is preset to a value for tuning the first local oscillator 446. A pad 455 follows the first mixer 452 to prevent overloading a second mixer 456 as well as to provide a good input termination for an image filter 458. The second IF 422 is chosen to produce and demodulate an IF frequency, e.g., 10.7 MHz, for which ceramic bandpasε filterε are readily available. A εecond frequency εyntheεizer 460, identical to the firεt frequency synthesizer 454, is used to phase lock a second local oscillator 462. A first ceramic filter 464 follows the second mixer 456 and setε the demodulation bandwidth. An IF amp 466 followε the first ceramic filter 464 and helps to limit the signal. A εecond ceramic filter 468 followε the IF amp 466 for additional band εhaping. A gain limiter amplifier 470 followε the second ceramic filter 468 for hard limiting. A quadrature detector 472 follows the limiter amplifier 470 and demodulates the FSK data. The input signal preferably deviates ±25 KHz and has a data rate of 140,625 bits per second. Demodulated data from the quadrature detector 472 enters a data slicer 474 where uncertain data edges are cleaned up, made absolute and fed to the controller 404 as the data output signal 406. In order to perform the inverse of the selected encoding rule, e.g., to insert the sync and blanking signalε, at precisely the correct position in time, the controller 404 is phase locked to the time reference provided from the synchronized signals at the headend. This time reference, originally generated from the common timing reference signal 109 at the headend, becomeε available to the controller 404 as part of the demodulated data signal 406. In this exemplary embodiment, the controller 404 performs the inverse of the selected encoding rule with a sync and blank generator that locks itself to the edge of a received reference pulse to avoid sync drift. In a preferred embodiment, this locking is accomplished by altering the clock frequency of the controller 404. In Figure 15, it iε εhown that the controller 404 iε comprised of a procesεor 476, preferably a microcontroller, executing software at a rate controlled by a voltage controlled crystal oscillator 478. The processor 476 sends a feedback signal 480 to a digital to analog converter 482 which drives the voltage controlled crystal oscillator 478 and effectively changes the clock frequency and thus the execution speed of the processor 476. By responsively altering the execution speed of the procesεor 476 in reεponse to the decoded data output signal 406, the channel select 430 and the second IF frequency select signals 432 are thus responsively altered, phase locking the data receiver 402 to the decoded data signal 406. As discussed in reference to the data modulator 116, data is only sent during prescribed periods, the vertical synchronization intervals. The controller 404, under εoftware control, recognizeε the reference pulse 304, and a combination of the first start sequence 306, the second start sequence 308 and the validity check byte 310, to ensure that the controller 404 is εynchronized with the common timing reference εignal 109. When an error iε encountered, the controller 404 alterε its clock frequency and/or the time window during which it looks for the data blockε 300 and 302. From the foregoing it εhould now be recognized that encryption/decryption method and apparatuε embodimentε have been diεcloεed herein which make a plurality of distributed television channels εimultaneouεly and automatically available to authorized εubεcriberε. Additionally, a single channel system using the diεclosed modulation and demodulation methods is also considered within the scope of the present invention. The previously disclosed invention can advantageously εimultaneouεly decode a block of televiεion channel εignalε. However, providers may still desire to block the reception of premium channelε, e.g., HBO, thus restricting subscribers to service tiers, e.g., 1) basic, 2) baεic plus expanded, 3) basic plus expanded plus selected premium channels, etc. To accomplish this task, the preεent invention uεes an interdiction device to selectively scramble television channel signals from within the block of locally decrypted channel signalε. Figure 17 εhowε the uεe of a preferred interdiction device 510 which selectively jams a multichannel television (TV) channel signal 512, an unencrypted signal, from a typical prior art television distribution syεtem (not εhown) to generate a εignal 514 to provided εubεcriberε with a plurality of unencrypted televiεion channel εignalε aε well as a plurality of εelectively encrypted/jammed channel εignals. While εuch a εyεtem can be uεed in various environments, e.g., over-the-air and conventional cable subscriber systems, it is particularly useful in combination with the previously disclosed decoder 400. In embodimentε of the present invention, the interdiction device 510 is programmable and capable of selectively scrambling a plurality of television channelε throughout the range of otherwiεe unencrypted televiεion channelε from εignal 512. Figure 18 shows a block diagram of the preferred mterdiction device 510. Embodiments of the present invention are based upon the recognition that television channels are allocated separate frequency slotε, εeparated by fixed amountε, e.g., 6 or 8 MHz. If a jamming εignal is properly isolated to a fixed channel, only that channel is disrupted/jammed without significantly effecting even adjacent channels. The preferred interdiction device 510 primarily compriseε: 1) a frequency synthesizer/VCO 516 (a jamming εignal generator) for generating a jamming signal, e.g., an FM-modulated sine wave, 2) a controller 518 for directing the frequency synthesizer/VCO 516 to generate a jamming, signal 520 for a selected television channel, 3) a mute switch 522 under control of the controller 518 for only enabling the output of the jamming signal 520 when the frequency syntheεizer/VCO 516 haε locked to a predetermined jamming frequency for each selected channel, and 4) a summer 524 for combining the multichannel television channel signal 512 and the generated jamming signal 520 passed by the mute switch 522. The controller 518 contains a channel interdiction table 526, which corresponds to the preselected channels that are to be jammed. Each of these channels correspond to specific frequencies for each geographical area, e.g., USA, Europe, etc., and to particular transmisεion standards, e.g., NTSC or PAL. (See, e.g., Table I below depicting frequency assignmentε for a VHF Syεtem M (6 MHz) USA.) A εecond table (not shown) within the controller 518 is preferably used to convert each channel designation to its corresponding frequency. Alternatively, table 526 may directly contain frequency designationε correεponding to the εelected channelε. The table 526 may alternatively be preloaded, e.g., εtored in nonvolatile memory, or may be loaded via communication between the controller 518 and εome external device, e.g., via a communication interface 527. Alternatively, aε deεcribed further below, the multichannel televiεion εignal 512 can contain authorization data via the communication interface which can be decoded to instruct identified controllers 518 to add or delete entries from its channel interdiction tableε 526. // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // TABLE I The controller 518 commandε the frequency synthesizer/VCO 516 via a control interface 528 comprised of a frequency select bus 530 (used to select the desired jamming frequency corresponding to a selected channel) and a lock signal 532 (used to provide a feedback statuε signal) . The frequency synthesizer/VCO 516 takes a diεcrete, i.e., a nonzero, amount of time (a function of the deεign of the frequency syntheεizer/VCO 516) to lock to the deεired jamming frequency. Once the deεired jamming frequency iε achieved, the jamming frequency is preferably maintained for a period of time before a next jamming frequency is selected. The lock signal 532 is then generated by the frequency syntheεizer/VCO 516 which can be uεed to notify the controller 518 that the deεired jamming frequency haε been achieved. Preferably, the lock εignal 528 iε generated by a frequency comparator within the frequency εyntheεizer/VCO 516 which compares the jamming signal 520 to the frequency commanded by the controller 518. Once the controller 518 haε been informed that a lock haε been achieved, the mute εwitch 522 iε commanded via a mute control signal 534 to permit the jamming signal 520 to be passed via signal 536 and summed by the summer 524 with the multichannel television channel signal 512, thuε generating the selectively scrambled multichannel televiεion signal 514. This process is repeated for each of the frequencies/channels εpecified in the table 526. Figure 19 iε a simplified block diagram that summarizeε the previouεly described process. In block 538, the controller 518 selects the next frequency from the channel interdiction table 526. After waiting during block 540 for the frequency syntheεizer/VCO to reach the εelected frequency, the controller 518 in block 542 inεtructs the mute switch 522 via the mute control signal 534 to commence jamming the selected television channel. In block 540, the controller alternatively waits a predetermined time period or waits for the lock signal 532 to be returned from the frequency syntheεizer/VCO 516. In a preferred implementation, there iε no timing relationεhip required between the timing of the εelected television channel and the jamming signal. Conεequently, the output of the mute εwitch 522 must be maintained during block 544 for a sufficient time period, e.g., at least one frame period, to adequately jam the selected television channel. At the end of the time period defined in block 544, the controller in block 546 enables the mute εwitch 522 via the mute control signal 534 (if the next channel to be interdicted is not adjacent to the current channel) . The process then cyclically repeats, starting at block 538, with the next entry in the channel interdiction table 526. As should be apparent to one of ordinary skill in the art, there are two time periods involved in this cyclical process, a first time period related to the lock time in block 540 and a second time period defined by the predefined time period in block 544. Accordingly, there is a maximum cycle rate (for a particular implementation) , that this process can be repeated. This cycle rate determines the maximum number of channels (five in an exemplary embodiment) that can continuously (as viewed by a subscriber) be interdicted. Accordingly, in an alternative embodiment, a plurality of frequency synthesizer/VCOs 516 are multiplexed such that one can be approaching its jamming frequency (in block 540) while another is dwelling at its jamming frequency (in block 544) . Consequently, the number of interdicted channels can be increaεed. Figure 18 additionally εhowε the baεic εtructure of the preferred frequency synthesizer/VCO 516 which is primarily comprised of 1) a video frequency synthesizer 548, 2) an audio frequency syntheεizer 550, 3) a summer 552, and 4) a VCO 554 (voltage-controlled oscillator) . In an exemplary embodiment, the video frequency syntheεizer 548, e.g., a National LMX1511A or Fujitεu MB15A02, is commanded to select a particular frequency, e.g., the base video carrier frequency of the television channel offset by a jam frequency, e.g., a frequency approximately half way through the television channel or approximately 3 MHz, via the three wire bus 530 comprised of clock, data, and enable signals (an interface particularly well- suited for sharing with additional frequency syntheεizerε) . The frequency synthesizer 548 generates an analog video VCO control signal 556 that commands the VCO 554 to generate the desired frequency. A feedback signal 558 is returned to the frequency syntheεizer 548 where it is compared in frequency with the frequency commanded by the controller 518. When a match is achieved the lock signal 532 results and this status signal is communicated to the controller 518. With reference to Table I, there is shown a table of the relevant frequencies for a VHF system M in the USA having 6 MHz slots allocated for each television channel. Ideally, the frequency synthesizer/VCO 516 would be tunable to the entire potential frequency range, e.g., 40-860 MHz, or more. Practically, this goal may not be easily achievable. Thus, in an exemplary embodiment the frequency synthesizer/VCO 516 is tunable between 260-422 MHz, corresponding to television channels 31-55. Let's say that an exemplary system was instructed to jam/interdict channels 44 and 50. Channel 44 has a video carrier of 343.25 MHz with the preferred jamming frequency at 346.25 MHz (343.25 MHz plus a preferred offset of 3 MHz). Similarly, the preferred jamming frequency of channel 50 is at 382.25 MHz (379.25 MHz plus a preferred offset of 3 MHz). Thus, by repetitively switching/dwelling between jamming frequencies of 346.25 and 382.25 MHz, channels 44 and 50 can be jammed while leaving the remaining channels unaffected. As described so far, the jamming signal will adequately disrupt only the video portion of the selected television channel. Therefore, a preferred embodiment additionally comprises the audio frequency synthesizer 550, which in an exemplary embodiment divides a frequency output 560 of the frequency synthesizer 548 to generate a digital audio VCO control signal 562. The analog video VCO control signal 556 and the digital audio VCO control signal 562 are summed by summer 552 to generate a VCO control signal 564 which controls the VCO 554 to generate a frequency-modulated jamming signal that will jam both the video and audio portions of the selected television channel. Figure 20 shows a preferred embodiment of the present invention comprised of the multichannel interdiction device 510 combined with the previously disclosed decoder 400. While the prior decoder 400 disclosed significant improvements over the prior art by permitting a single apparatus to simultaneously decrypt all or none of the transmitted channels according to transmitted authorization data, it did not permit the provider to restrict access to selected channels. With the present decoder/interdiction device combination 566, the microcontroller 518 receives authorization data from a data receiver 568 via its data output 570 that has been inserted at the headend to identify authorized subscribers (preferably identified with a predefined subscriber or box code in the microcontroller 518) . In this preferred embodiment, the same microcontroller 518 that controls the common decrypting of a commonly encrypted input source 572, loads the channel interdiction table 516 according to the authorization data, e.g., according to tierε. The data in the interdiction table 516 iε then uεed to control the operation of the frequency εyntheεizer/VCO 516 and the mute εwitch 522 uεing the control interface 528 and mute control εignal 534 according to the previously described algorithm. This improved combination now permits the simultaneouε reception of multiple unencrypted εignals (suitable for picture-in-picture use) while still permitting the provider to withhold access to selected channels. In order to adequately jam selected channels, it is preferable that a standardized jamming amplitude ratio be achieved between the jamming signal at the mute switch output 536 and the multichannel television channel signal 512. Without this standardization, undesirable results could occur. For example in a first mode, one might attempt to pirate a jammed television signal by amplifying the common scrambled input source 572 to overcome the jamming signal. However, if a standardized jamming amplitude ratio is maintained, the input source 572 would automatically be attenuated and this pirating attempt would fail. Conversely in a εecond mode, if an abnormally small input source 572 should be present, a proportionally large jamming signal could tend to spill over and effect adjacent channels. However, if the input source 572 is amplified, this undesirable effect would be minimized. To avoid these undeεirable reεults, a receive signal strength indicator (RSSI) 574 from the data receiver 568, indicative of the amplitude of the commonly scrambled input source 572 is used to control an AGC amplifier 576 to standardize the amplitude of a common attenuated signal 578 operated on within the decoder 400. By keeping the amplitude of the jamming signal fixed and continuously varying the common attenuated signal 578, a standardized jamming amplitude ratio can be achieved. Alternatively, an AGC amplifier could be used to control the amplitude of the jamming frequency. As previously described, authorization data is generally sent on a predetermined authorization data channel . However, in some embodiments, the predetermined channel can be varied to further limit pirating. As shown below in Table II, a preferred channel interdiction table can be structured to take advantage of these embodiments . In this N-value interdiction table, a first entry for each channel correspondε to a delta frequency from the authorization data channel frequency and a εecond entry εpecifieε whether this channel is to be interdicted. To attempt to defeat jamming, a pirate would need to know at least the present authorization data channel, any scheme for varying the authorization data channel, and the data within the interdiction table. Thus, pirating is further complicated. ENTRY OFFSET FROM DATA INTERDICT FREQUENCY CHANNEL Y/N N ΔF N Y/N TABLE II Additional improvements can be provided with this combination. Aε previously disclosed, the present decoder / interdiction device 566 can simultaneouεly decode all of the tranεmitted channelε by reverεing the encoding proceεε done to a plurality of εynchronized channels. Typically, this encoding is done by first synchronizing a plurality of video inputs at the headend and then suppressing the horizontal and vertical sync signal of the synchronized video inputs. Consequently, once the microcontroller determines the proper timing, a blanking control line 584 and sync control line 586 can simultaneously decode all of the received channels to generate the multichannel television channel signal 512, the input signal to the interdiction device 510. Since, there is a well-known temporal/timing relationship between the horizontal and vertical sync signalε, the preεent invention can take advantage of this relationship to optimize its temporal placement of the jamming signal 520 within each channel frequency range. Therefore, in this embodiment the predefined period of block 544 iε preferably defined by thiε known timing relationship; permitting the single frequency synthesizer/VCO 516 to jam a larger number of television channels. The preferred embodiments of the invention described herein are exemplary and numerous modificationε and rearrangements can be readily envisioned to achieve an equivalent result, all of which are intended to be embraced within the scope of the appended claimε. For example, the present invention can also be used with an unscrambled over-the- air system, e.g., a microwave signal after a downconverter that provides an unscrambled multichannel television signal. Additionally, the interdiction/jamming step can precede the simultaneouε decrypting step with similar resultε. // // // // // // // // // // // // // // // // //

Claims: CLAIMS 1. Subscriber site apparatus useful in a syεtem for diεtributing from a system headend 1) multiple channel signalε defining an RF band, each channel εignal having reεpective video synchronization components in time coincidence and 2) a common timing reference signal within said band and synchronouε with said synchronization components, and wherein each of said channel signals is encrypted in accordance with a common encoding rule, said subεcriber site apparatus comprising: a timing recovery circuit responsive to said common timing reference signal for generating at least one sync signal; and a single broadband decoder reεponεive to εaid εync εignal for simultaneously decrypting all of said channel signalε in accordance with the inverεe of εaid encoding rule to recover multiple decrypted channel εignalε εuitable for direct simultaneous application to a conventional televiεion receiver. 2. The apparatuε of claim 1 wherein a εelected channel εignal diεtributed from εaid headend iε encoded with authorization data and further compriεing a data decoder for extracting said authorization data from said εelected channel εignal to enable or diεable εaid broadband decoder in reεponεe to εaid authorization data. 3. The apparatuε of claim 1 wherein a selected channel signal distributed from said headend is encoded with said common timing reference signal and wherein said timing recovery circuit demodulates said selected channel signal to recover said common timing reference εignal. 4. The apparatuε of claim 1, wherein said broadband decoder includes a variable gain apparatus used for simultaneouεly amplitude modulating, εynchronouε with εaid recovered common timing reference εignal, said channel signals in accordance with the inverse of said encoding rule. // // 5. The apparatus of claim 4, further including a phase lock apparatus to synchronize said use of said variable gain apparatus with said common timing reference signal. 6. The apparatus of claim 5, wherein said phase lock apparatus comprises: an oscillator generating a clock frequency in response to a control signal; and a procesεor, executing εoftware to control εaid variable gain apparatuε at a rate reεponεive to εaid clock frequency; said procesεor additionally being reεponεive to said recovered common timing reference signal by altering said control signal. 7. The apparatus of claim 4, wherein said variable gain apparatus reinsertε said synchronization components into said channel signals in response to said common timing reference signal. 8. The apparatus of claim 1, further comprising meanε for periodically inεerting a jamming εignal into at leaεt one of εaid multiple decrypted channel εignalε to render it incapable of directly cauεing εaid televiεion receiver to produce an intelligible image. // // // // // // // // // // // // // // // 9. Subεcriber site apparatus useful in a syεtem for distributing from a syεtem headend 1) multiple channel εignals defining an RF band, each channel signal having respective video synchronization components in time coincidence and 2) a common timing reference signal within said band and εynchronouε with εaid εynchronization components, and wherein each of said channel signalε iε encrypted in accordance with a common encoding rule, εaid εubεcriber εite apparatus comprising: a timing recovery circuit responεive to said common timing reference signal for generating at least one sync signal; a single decoder reεponεive to εaid common εync εignal for εimultaneouεly decrypting all of εaid channel signals in accordance with the inverse of said encoding rule to generate multiple decrypted channel signalε, each capable of directly causing a conventional television receiver to produce an intelligible image; and an interdiction apparatus for periodically inserting a jamming signal into at least one of εaid multiple decrypted channel εignalε to render it incapable of directly causing said television receiver to produce an intelligible image. 10. The apparatuε of claim 9, wherein εaid interdiction apparatuε compriεeε: a jamming signal generator for generating a jamming signal capable of disrupting reception of a single selected channel within said multiple decrypted channel signalε; a controller for commanding εaid jamming εignal generator to generate εaid jamming εignal; an interdiction table coupled to εaid controller, εaid table capable of εtoring data to identify a plurality of selected decrypted channel signalε to be jammed; a mute switch under control of said controller for selectively pasεing said jamming signal; and a summer for combining said pasεed jamming εignal with εaid multiple decrypted channel εignalε. // // 11. The apparatus of claim 10, wherein said jamming signal generator is comprised of: a frequency synthesizer capable of being commanded by said controller to generate a frequency to jam said εelected channel εignal, said synthesizer generating an analog control signal representative of εaid jam frequency; a VCO controlled by εaid analog control signal to generate εaid jamming εignal; and a frequency comparator to compare εaid commanded frequency and said jamming signal to generate a lock signal when said commanded frequency and said jamming signal match. 12. The apparatus of claim 11, wherein said jamming signal generator is additionally compriεed of an audio frequency generator controlled by said frequency synthesizer to generate a second control signal to command said VCO to alter itε jamming signal to additionally contain frequency components to jam the audio portions of said selected channel εignalε. 13. The apparatus of claim 10, additionally comprising a lock signal generated by said jamming signal generator when said jamming εignal correspondε to εaid command from εaid controller. 14. The apparatus of claim 13, additionally comprising a mute control signal generated by said controller for commanding said mute switch to pasε εaid jamming signal in responεe to said lock εignal. 15. The apparatus of claim 10, wherein said controller also controls said decoder. 16. The apparatus of claim 10, wherein εaid controller loadε data into εaid interdiction table according to authorization data received from within εaid RF band. // // // // 17. A method of selectively scrambling television channels from an encrypted multichannel television signal at a subscriber site, comprising the steps of: simultaneously decrypting said encrypted multichannel television signal to form a decrypted multichannel television signal; determining an interfering frequency for a selected television channel signal according to an interdiction table containing data related to a plurality of channel signals selected to be scrambled; commanding a frequency generator to generate an output of said interfering frequency; waiting until said frequency generator has locked to said interfering frequency; enabling combining of said output of said frequency generator with said decrypted multichannel television signal; dwelling for a predetermined time period to scramble said selected television channel signal; disabling combining of said output of said frequency generator from said decrypted multichannel television signal; and cyclically repeating said previously recited steps for a next selected television channel signal. 18. The method of claim 17, wherein said dwelling period is synchronized with video synchronization signals from within each said selected television channel signal. // // // // // // // // // // // 19. Subscriber site apparatus useful in a system for distributing from a system headend 1 ) multiple channel signals defining an RF band, each channel signal having respective video synchronization components in time coincidence and 2) a common timing reference signal within said band and synchronous with said synchronization components, and wherein each of said channel signals is encrypted in accordance with a common encoding rule, said subscriber site apparatus comprising: an interdiction apparatus for periodically inserting a jamming signal into said RF band to generate an interdicted RF signal; a timing recovery circuit responsive to said common timing reference signal for generating at least one sync signal; and a single decoder responsive to said sync signal and said interdicted RF signal to simultaneously decrypt multiple channel signals in accordance with the inverse of said encoding rule to generate a recovered multichannel signal comprising multiple decrypted channel signals capable of directly causing a conventional television receiver to produce an intelligible image and at least one scrambled channel signal incapable of directly causing said television receiver to produce an intelligible image. // // // // // // // // // // // // // // // // 20. A method of distributing multiple video signals, each produced by a different video source at a syεtem headend and each containing picture and εynchronization componentε, to a plurality of εubεcriber εiteε located remote from said headend, said method comprising the steps of: generating at said headend multiple carrier signalε; modulating at said headend each of said carrier signalε with a different one of εaid video εignals to form multiple channel signalε, all of εaid channel signals having their respective video signal synchronization componentε in time coincidence; generating a common timing reference signal synchronouε with said time coincident synchronization components; causing each of said channel signals to be encrypted at said headend in accordance with a common predetermined encoding rule; modulating a selected encrypted channel signal in response to said common timing reference signal; distributing said multiple encrypted channel signals from said headend to said subεcriber siteε as a common RF signal; responding at each subscriber site to said common timing reference signal to simultaneously decrypt all of the channel signals distributed thereto by operating upon said common RF signal with a single decoder in accordance with the inverεe of εaid encoding rule to generate multiple decrypted channel signalε, each capable of directly cauεing a conventional televiεion receiver to produce an intelligible image; and periodically inεerting at each εubεcriber εite a jamming εignal into at leaεt one of εaid multiple decrypted channel εignalε to render it incapable of directly causing said television receiver to produce an intelligible image. // // // // 21. A method of distributing multiple video signals, each produced by a different video source at a system headend and each containing picture and synchronization components, to a plurality of subscriber sites located remote from said headend, said method comprising the steps of: generating at said headend multiple carrier signals; modulating at said headend each of said carrier signals with a different one of said video signals to form multiple channel signals, all of said channel signals having their respective video signal synchronization components in time coincidence; generating a common timing reference signal synchronous with said time coincident synchronization components; causing each of said channel signals to be encrypted at said headend in accordance with a common predetermined encoding rule; modulating a selected encrypted channel signal in response to said common timing reference signal; distributing said multiple encrypted channel signals from said headend to said subscriber sites as a common RF signal; periodically inserting a jamming signal at each subscriber site corresponding to at least one encrypted channel signal into said common RF signal to generate an interdicted RF signal; and responding at each subscriber site to said common timing reference signal and said interdicted RF signal to - simultaneously decrypt multiple channel signals distributed thereto with a single decoder in accordance with the inverse of said encoding rule to generate multiple decrypted channel signals capable of directly causing a conventional television receiver to produce an intelligible image and at least one scrambled channel signal incapable of directly causing said television receiver to produce an intelligible image. // // // 22. Apparatus for distributing multiple video signals, each produced by a different video source at a system headend and each containing picture and synchronization components, to a plurality of subscriber sites located remote from said headend, the apparatus comprising: a plurality of modulators at said headend for generating multiple carrier signals; a plurality of frame synchronizers at said headend for modulating each of said carrier signals with a different one of said video signals to form multiple channel signals, all of said channel signals having their respective video signal synchronization components in time coincidence; a timing reference generator at said headend for generating a common timing reference signal synchronous with said time coincident synchronization components; a plurality of encoders at said headend for causing each of said channels signals to be encrypted in accordance with a common predetermined encoding rule; a data modulator at said headend for modulating a selected encoded channel signal in response to said common timing reference signal; means for distributing said multiple encrypted channels signals from said headend to said subscriber sites as a common RF signal; a timing recovery circuit at each subscriber site responsive to said common timing reference signal for generating at least one sync signal; and a single decoder at each subscriber site to respond to said sync signal to simultaneously decrypt all of the channel signals distributed thereto by operating upon said common RF signal decoder in accordance with the inverse of said encoding rule to generate a recovered signal comprising multiple decrypted channel signals suitable for direct simultaneous application to a conventional television receiver. // // // // // 23. The apparatus of claim 22, further comprising an interdiction apparatus for periodically inserting a jamming signal into said recovered signal to generate an interdicted signal comprising multiple decrypted channel signals each capable of directly causing a conventional television receiver to produce an intelligible image and at least one scrambled channel signal incapable of directly causing said television receiver to produce an intelligible image. // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // 24. Apparatus for distributing multiple video signals, each produced by a different video source at a system headend and each containing picture and synchronization components, to a plurality of subscriber sites located remote from said headend, the apparatus comprising: a plurality of modulators at said headend for generating multiple carrier signals; a plurality of frame synchronizers at said headend for modulating each of said carrier signals with a different one of said video signals to form multiple channel signals, all of said channel signals having their respective video signal synchronization components in time coincidence; a timing reference generator at said headend for generating a common timing reference signal synchronous with said time coincident synchronization components; a plurality of encoders at said headend for causing each of said channels signals to be encrypted in accordance with a common predetermined encoding rule; a data modulator at said he dend to data modulate a selected encoded channel signal in response to said common timing reference signal; means for distributing said multiple encrypted channels signals from said headend to said subscriber sites as a common RF signal; an interdiction apparatus at each subscriber site for periodically inserting a jamming signal into said recovered signal to generate an interdicted signal; a timing recovery circuit at each subscriber site responsive to said common timing reference signal for generating at least one sync signal; and a single decoder responsive to said sync signal and said interdicted RF signal to simultaneously decrypt said interdicted signal in accordance with the inverse of said encoding rule to generate a recovered multichannel signal comprising multiple decrypted channel signals capable of directly causing a conventional television receiver to produce an intelligible image and at least one scrambled channel signal incapable of directly causing said television receiver to produce an intelligible image.

Inventors: LIE YAT SEN, MILIANI PABLO, PETREE DAVID L, LIE, YAT, SEN, MILIANI, PABLO, PETREE, DAVID, L.
Applicants: CALIFORNIA AMPLIFIER
Application year: 1995
Main classification: H04N7
IPC codes: H04N7