Abstract:
Illegal cable decoders, i.e., black boxes, are defeated by adding, inserting and/or superimposing an added signal onto an already scrambled video signal, which added signal is capable of disrupting the operation of the illegal cable decoder. As a result of the added signal, the illegal cable decoder outputs an unstable or unviewable picture or signal and concealment is maintained. In another embodiment of an added signal, a modulated signal with a range from about blanking level to about peak white level is added, inserted and/or superimposed on the unstable scrambled video signal in the vertical blanking interval and/or its vicinity. As a result, the illegal cable decoder is caused to generate some horizontal instabilities at its output. For those illegal cable decoders that utilize color burst as a means to decode, methods to defeat these consist of filling in color burst in the vertical blanking interval area and/or modifying the position of the correct burst while adding an incorrect frequency burst to defeat the illegal cable decoder.

Description:
REFERENCE TO PROVISIONAL APPLICATION 
     This application claims priority to provisional application Ser. No. 60/093,705 filed Jul. 22, 1998 and Ser. No. 60/100,043 filed Sep. 11, 1999. 
     CROSS REFERENCE TO RELATED APPLICATIONS 
     This invention is related to International Application PCT/US98/05163 filed on Mar. 17, 1998, by Quan; U.S. Provisional Application 60/069,815 filed on Dec. 15, 1997, now U.S. application Ser. No. 09/212,336 filed Dec. 15, 1998, and U.S. Provisional Application 60/076,087 filed Feb. 26, 1998, now U.S. application Ser. No. 09/233,922 filed Jan. 22, 1999, by Quan. It is also related to U.S. Pat. No. 5,438,620 by Ryan et al. issued on Aug. 1, 1995. All the above are incorporated by reference. 
    
    
     FIELD OF INVENTION 
     This invention relates to video cable scrambling systems, and more particularly relates to a method and apparatus for inserting or otherwise adding a jamming signal in a video signal to defeat the illegal video cable decoders also known as cable “black boxes”. 
     BACKGROUND OF INVENTION 
     In many scrambled cable systems today, illegal cable black boxes are used to present a viewable or stable picture. These cable black boxes are effective in neutralizing sync suppressed scrambled video systems. It has also been found that some video scrambling systems using vertical sync suppression and/or horizontal sync modulation are also vulnerable to these cable black boxes. By using relatively simple circuitry with at least one manual control, the operator with a cable black box adjusts the control until a viewable picture is seen. 
     Referring to the  FIG. 1 , in those black boxes with at least one adjustment, the video level is adjusted via an amplifier  12 , and then supplied to a low pass filter  14  and a comparator  16 . The comparator then generates a vertical timing signal V reset for a television sync generator circuit  18  which also receives a horizontal timing signal from a filter/slicer circuit  20 . Once a reliable vertical reset pulse is established (output) by the comparator  16 , the sync generator circuit  18  delivers composite sync for a viewable picture via a switcher  22 . Even with sync suppressed video signals, the comparator  16  picks out the normally blanked lines in the vertical interval and generates a suitable vertical reset signal. 
     In yet another type of cable black box, the color burst of the video signal is used for illegal decoding. In this case, the lack of color burst in some lines of the vertical, blanking interval identifies the vertical sync area. Thus, for a cable black box such as shown in  FIG. 2 , the color burst is relied upon to provide the illegal decoding process. More specifically, the lack of burst in the vertical blanking interval (VBI) allows for the illegal generation of a reliable vertical rate reset signal. The fact is that in most video signals, scrambled or not, burst is not present for about 9 lines in the VBI. Thus in  FIG. 2 , the scrambled video signal is bandpass filtered in a filter  24  to provide a burst envelope signal which is supplied to a detection amplifier  26  and a phase lock loop (PLL) circuit  28 . The detection amplifier senses the burst envelope. A one shot  30  triggers off the burst envelope leading edge and supplies a pulse which extends into the next video line (e.g., is 50 microseconds) and thus is referenced to the color burst, not the video signal. A one shot  32  provides a short pulse (of about 2 to 3 microseconds) as a burst gate to the PLL circuit  28 , which also receives the burst envelope signal. The PLL circuit  28  supplies a burst signal and a clock reference to a sync regenerator circuit  36 . A retriggerable one shot  34  is triggered by the one shot  30  pulse and provides a pulse which is slightly longer than one video line, and which thus extends through the active video field so that the one shot  30  no longer sees the burst envelope. At this point the retriggerable one shot  34  turns off during most of the VBI (e.g., for about 20 video lines). Thus, the output of one shot  34  comprises a regenerated vertical rate pulse, which is supplied to the sync regenerator circuit  36 . The latter circuit  36  supplies new sync/burst signals as well as an insert control signal to a switch circuit  38 . The switch circuit  38  also receives the scrambled video signal and, in response to the insert control signal, inserts the new sync/burst signals to descramble the signal sufficiently to provide a viewable video signal to an unauthorized user via an amplifier  40 . 
     SUMMARY OF THE INVENTION 
     It is then an object of the present invention to counter illegal cable black boxes by providing modifications in the scrambled signal to neutralize and/or offset the illegal operation of the cable black boxes. 
     To illustrate, with regards to the illegal black box circuit of  FIG. 1 , the present invention provides an added signal which jams or disrupts the illegal operation of the black box. Thus, a key to creating the added signal, that is, an unreliable vertical signal for the cable black box of  FIG. 1 , is to cause the comparator, e.g., comparator  16 , to generate an erroneous vertical reset signal. In an embodiment of this invention, lines near and within the vertical blanking interval are modified. This modification can consist of removing the broad vertical pulses of the vertical sync and then adding and/or inserting a jamming, i.e., unreliable, vertical signal in lines near the bottom and top portions of the active field. This jamming signal is also added or inserted to lines in the vertical blanking interval (VBI) that do not have data and/or reference signals. For simplicity, the unreliable vertical signal can be a time varying (for example, pedestal) voltage, of about blanking level to about peak white video level, during at least a portion of each modified horizontal line. As a result of the unreliable vertical signal around and within the vertical blanking interval area, the cable black box (such as shown in  FIG. 1 ) outputs an unstable video signal, resulting in a concealed picture. 
     With regards to the black box typified in  FIG. 2 , the present invention again provides an added signal which jams or disrupts the operation of the black box. To defeat this type of black box, new color burst can be put into those lines normally lacking color burst in the VBI. Color burst itself may also be modified, in frequency for example, such that only an authorized decoder can transform a modified burst into the correct one. Alternate variations to that of modifying the burst can be an added signal in the form of a change in burst location, that is, in line and/or pixel locations. Also the burst signal itself may be modified so that the cable black box receives the wrong color burst signal (i.e. burst frequency) while the authorized decoder senses the correct color burst. By making the cable black box sense the wrong burst, the timing circuitry within the cable black box will deliver erroneous counts thereby causing an unstable video signal output. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a typical illegal cable television decoder with adjustment for video gain and/or threshold levels. 
         FIG. 2  illustrates another illegal cable decoder that relies on the use of color burst. 
         FIG. 2A  illustrates a standard color burst for a television signal. 
         FIG. 2B  illustrates a modification of color burst in accordance with the present invention by placing a wrong color burst signal where normal color burst is and then relocating normal color burst elsewhere. 
         FIG. 2C  illustrates a variation in the present invention of placing a wrong color burst signal in the sync area vicinity to upset the cable black box relying on burst. Normal burst is relocated elsewhere as depicted. 
         FIG. 3A  illustrates a conventional television signal in the region of the vertical blanking interval (VBI) and its vicinity. 
         FIG. 3B  illustrates a modified television signal for defeating a cable black box such as that illustrated in FIG.  1 . The vertical (broad) sync pulses are removed and/or modified. Also lines designated by “A” have a jamming signal inserted and/or added. The jamming signals cause the cable black box to mis-trigger and produce an unstable output. 
         FIG. 3C  illustrates a modified television signal for defeating a black box such as that of  FIG. 2 , wherein color burst is inserted and/or added to those lines in the VBI vicinity that lacks color burst. The inserted and/or added burst is designated by “B”. Note these added and/or inserted color bursts can be applied to the technique of  FIG. 3B  as well. 
       FIG.  4  and  FIG. 5  are block diagrams illustrating circuitry in accordance with the invention for defeating cable black boxes typified in FIG.  1 . 
         FIG. 6  is a block diagram illustrating circuitry in accordance with the invention for defeating a cable black box typified in FIG.  2 . 
         FIG. 7A  illustrates a modified color burst signal of the invention where the color burst frequency is not necessarily the correct frequency. The frequencies of color burst (envelopes) F1 and/or F3 are different from the nominal burst frequency, and may be changed from line to line or field to field. 
         FIG. 7B  illustrates a modified optional color burst signal of the invention F5 for reference, and includes on that line color burst reference frequencies, F2 and F4. 
       FIG.  7 C and  FIG. 7D  are block pictorial diagrams of the invention, illustrating how mixing for the sum frequency of F1 and F2, or F3 and F4 produces the correct color frequency the encoder and/or authorized decoder. 
         FIG. 7E  is a block pictorial diagram of the invention, illustrating how the correct combination of frequencies F2 or F4 is used to generate the correct color subcarrier frequency for the authorized decoder, using the DATA for the decoder. 
         FIG. 8A  illustrates a conventionally scrambled signal with position modulated syncs. 
         FIG. 8B  illustrates a slightly improved scrambled signal which adds an edge-fill and/or added signal with edge modulation. S1 denotes a standard slice level for a sync separator, while S2 denotes the slice level for an illegal cable black box which still can provide a viewable picture. 
         FIGS. 9A-B  illustrate a modification in the technique of  FIG. 8  where the edge fill signal now includes a form of amplitude modulation, with  FIG. 9C  depicting an associated circuit. 
         FIGS. 10A-10K  are waveforms illustrating various timing signals related to the edge fill modulation circuitry of FIG.  11 . 
         FIG. 11  is a block diagram of the invention illustrating an implementation of the apparatus for providing the improved scrambling signals to defeat illegal cable decoders and/or TV sets. 
         FIGS. 12A-12D  are waveforms illustrating portions of the video signal waveform that are modified so that an illegal cable decoder can be “fooled” into sensing the wrong vertical rate signal. 
         FIG. 13  is a block diagram illustrating an implementation of the invention for generating, for example, the waveforms shown in FIGS.  12 A-C. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates an illegal cable black box that works by adjusting the video level and/or bias voltage into the high gain amplifier  12  of previous mention. Generally in a scrambling system, there are some lines in the VBI vicinity that are of fixed level (i.e., around blanking level). By adjusting the video gain and or bias into the inputs of the comparator  16 , a vertical rate (V Reset) signal is produced. V Reset synchronizes the sync generator circuit  18  in a vertical fashion. Optional horizontal timing into the sync generator circuit is established by extracting horizontal rate signals via the filter/slicer circuit  20 . Circuit  20  may be similar to circuit  16  and may also have filters and phase lock loop oscillators and/or slicing circuits. The sync generator circuit  18  then reinserts a stable sync into the video signal via the switching circuit  22 , whose output then is a video signal with replaced stable syncs and a viewable picture. 
     It should be noted that if vertical sync pulses are present in a scrambled signal, the decoder of  FIG. 1  will decode without too much problem. If the scrambled signal is missing vertical sync signal, then the circuit of  FIG. 1  will “slice” or detect at a level around or above blanking level. Since there is usually at least one line in the VBI vicinity near blanking level, a somewhat stable vertical rate signal will be available through the comparator  16  and a somewhat stable picture will be displayed. Under these conditions, the operator may have to periodically readjust the video gain and/or bias (slicing threshold of comparator  16 ) for a stable picture when the average picture level of the program video varies. 
       FIG. 3B  shows a solution to neutralizing the cable black box by removing (at least some of) the broad vertical sync pulses and/or eliminating some of the pre and post horizontal equalizing pulses and adding a jamming signal in lines, as designated by the notation “A”, wherein “A” designates the lines available for inserting the jamming signal in the VBI and its vicinity in accordance with the invention.  FIG. 3A  illustrates a conventional television signal in the VBI and vicinity. It is acknowledged that in scrambling systems, there are always some television lines reserved for DATA and reference signals in the VBI area. Therefore for authorized decoder compatibility, the jamming signal will be inserted, for example, in the VBI where there are no DATA and/or reference signals for the authorized decoder, and in the lines before and after the VBI. Because of overscan conditions in television sets, some of the jamming signals can be placed about 5 lines before and/or after the VBI. In some cases, the DATA and reference signal can tolerate a level shifted signal added to cause problems for the cable black box. The jamming signal can be a fixed or varying signal. For a fixed signal, for example, a 30% white signal may suffice. For a varying signal, the last few lines of the active field can be averaged and the average voltage can be used as the jamming signal. 
     Yet another method of the invention is to interpolate the average luminance voltage from the bottom of the field to the top of the field. This interpolated (average) voltage then is used to “fill” in the lines in the VBI. See the waveforms  46 ,  48  (or  53 ,  55 ) of the circuit of FIG.  4 . Filling in the non data and/or reference lines with a jamming signal in accordance with the invention, causes a black box operator to have to constantly readjust the cable black box for momentary stability. Part of the reason there is momentary stability is that the black box now is using the video signal as a source for a vertical rate reset signal. When the average picture levels change during the video program, the black box will have a different threshold level for a vertical reset signal which requires the continuous operator readjustment. 
     The preferred jamming signal (for, e.g.  FIG. 1 ) is to insert and/or add a voltage that varies, or is in the range, from about blanking level to about peak white level. In this manner, the jamming signal may be amplitude, and/or position and/or pulse width modulated. The rate of modulation can be, for example, at about 11 Hz (periodic or random), although many other frequencies or waveforms will also cause black box instabilities. Note, each filled line may also have independent (for example, jamming) source generators. In the preferred embodiment, the varying signal is asynchronous with the video field rate, and thus causes the black box&#39;s comparator to generate unstable vertical signals. 
       FIG. 4  thus illustrates a block diagram of a circuit for neutralizing a cable black box of the type illustrated in FIG.  1 . Video is fed to a low pass filter  50  to average the luminance (luma) video voltage. Sample and hold circuits  52 ,  54  then store the average bottom picture and top picture luminance values, respectively, as depicted by waveforms  53 ,  55  (or  46 , 48 ). A switch  56  supplies thus a signal that contains the bottom TV field luminance values before the VBI and the top TV field luminance values during the VBI. An interpolation filter  58  such as a low pass filter, filters the output of switch  56  and supplies it to a summing circuit  60 . The other input to summing circuit  60  is a signal source, such as a varying voltage, VN1, varying over a voltage range within the overall range of from about blanking to about peak white level. The output of summing circuit  60  then supplies an interpolated voltage ranging from the bottom picture luminance values to the top picture luminance values, plus any “dithering” supplied from VN1. The dotted lines on the waveforms  46 ,  48  show examples of the interpolated response of filter  58 . 
     For a simpler approach, one can store the average luminance values from the bottom TV field and add an optional dithering voltage, VN2. Although VN2 may be similar to VN1, it may be independent. This is done through a summing circuit  62 . Of course if a constant voltage (i.e., 30% white level) is chosen, then a voltage V 14  is connected to an input of the summing circuit  62  via a selector circuit  64  with the additional optional dithering noise voltage VN2 supplied to circuit  62 . If just a varying voltage is desired, then VN2 can be set to vary and the other input of the summing circuit  62  can be set to zero for example. A selector circuit  66  is coupled the outputs of the summing circuits  60 ,  62  and thence to one input of a switch  68 . 
     The video is fed to a timing circuit  70  to generate signals coincident with the VBI, top and/or bottom portion of the TV field, and DATA and/or reference signal line location. Timing circuit  70  also generates a signal VSYNCR that controls the removal (or reduction) of the vertical sync (i.e., broad vertical signal pulses). A switch circuit  72  is activated by the signal VSYNCR and outputs a signal substantially free of vertical sync signals. Because the broad vertical sync pulses are removed, it may be necessary to supply a new vertical sync identification signal, VSYNC ID for authorized decoding. VSYNC ID can be a signal anywhere in the video signal and does not have to be of field rate. The signal VSYNC ID is inserted via a switch circuit  74  whose output then is a video signal without standard vertical sync signal with an identification signal for the authorized decoder (identified as VSYNC ID). 
     The timing circuit  70  inserts the jamming signal by controlling the switch  68  of previous mention. An AND circuit  76  and an inverter  78  control the insertion of the signal from the selection circuit  66  or the switch  74  during the active lines in the VBI area (and/or lines near it) not necessarily including lines with DATA or reference signals in the VBI. The output of an amplifier  80  then has jamming signals inserted and vertical syncs removed or reduced, to cause instabilities for a cable black box of the type for example in FIG.  1 . 
       FIG. 5  illustrates an alternative embodiment of a circuit that inserts wider than normal horizontal sync pulses (one or more per TV field) to the video signal at a preferably non synchronous rate (for example 27 HZ). This wide horizontal sync pulse is used to further cause instabilities in the cable black box. By inserting wider than normal horizontal syncs, the cable box may sense these as vertical sync pulses. Since these pulses occur preferably asynchronously to the field and/or frame rate, the cable black box develops an erroneous vertical reset upon detecting them. A circuit  82  inserts the wider than normal sync pulses along with a color burst. 
     A horizontal rate signal, WHBI, which is about 13 microseconds for example and may be supplied from  FIG. 4 , is fed to one input of an AND gate  84 . WHBI also is supplied to an inverter gate  86 , whose output is used to clock in an asynchronous signal, VGEN. The signal VGEN can be any waveform such as for example, a 27 HZ signal. VGEN is fed to the “D” input of a flip flop  88 , whose output is fed to an optional one line one shot, or half shot, timing circuit  90 . The output of timing circuit  90  (if used) is fed to the other input of the AND gate  84 , whose output becomes logic high for a duration of about 13 microseconds (for example) at a 27 Hz rate and during a widened horizontal blanking interval. The switch  82  then inserts the wide or modified sync with color burst accordingly into the incoming video signal, which then is outputted via an amplifier  92 . 
     To neutralize the cable black box, such as in  FIG. 2 , the color burst can be modified such as in  FIG. 2B , FIG.  2 C and/or  FIG. 3C  to cause the cable black box to generate an unstable output. In contrast,  FIG. 2A  illustrates a standard color burst signal in an HBI. Modifications as illustrated in  FIG. 2B  or  FIG. 2C  that have the wrong color burst frequency will cause the cable black box to count incorrectly in its sync regeneration circuit. When the VBI is filled with color burst, leaving no lines in the television signal without burst, the cable black box then has no way of referencing a vertical signal. Note the burst filled in the VBI as shown in  FIG. 3C  may have normal color burst and/or the type of burst modifications as shown in FIG.  2 B and FIG.  2 C. Also burst may be reduced or modified at various locations in the VBI vicinity so as to cause the cable black box to have an unstable vertical signal. 
       FIG. 6  illustrates a way to modify a video signal such that the burst has incorrect frequencies. To this end, video is fed to a sync separator/timing circuit  94 . A burst phase lock loop oscillator  96 , is locked to the input&#39;s video signal. A generator  98  with the incorrect frequency is fed to a modified burst inserter circuit  100 . Circuit  100  also receives timing and color burst signals as well. The output of circuit  100  then generates a video signal that causes cable black boxes dependent on burst to misbehave while allowing an authorized decoder to work properly. 
       FIG. 7A  illustrates a burst modification provided, for example, throughout the active field including the VBI. This modification applies the burst at a frequency such that the cable black box will lock to an erroneous frequency and thus cause an unstable output. To recover the thusly scrambled signal, the correct color frequency, at least one line per field for example, is set aside for reference signals as shown in  FIG. 7B. A  correct color frequency is provided by multiplying the modified bursts of  FIG. 7A  by a continuous wave version of frequency F2 or F4. The continuous wave version of F2 and/or F4 is accomplished by known phase lock loop oscillator techniques. With the scrambler&#39;s DATA as a control signal, the correct frequency is chosen for authorized decoding.  FIG. 7E  illustrates at the output of a band pass filter  102  (BPF) the correct color subcarrier frequency and/or phase, provided by a multiplier  104  and selected frequencies F1 or F3 with F2 or F4. 
       FIGS. 7C and 7D  are simple examples of multiplying selected bursts by selected continuous wave frequencies. It should be noted that two different pairs of frequencies (for modified burst and reference frequency) can be used for extra security, as shown in FIG.  7 E. 
     Referring back to  FIG. 1 , one can see that the cable black box achieves its “sync” signal by providing slicing for the sync separator at levels generally above blanking level. See RADJ and RBIAS of FIG.  1 . Thus, the inserted and/or added jamming signals in the VBI vicinity ( FIG. 3B  for example) cause erroneous vertical reset signals for the cable black box. The reason is that the jamming signals are the signals that are sliced or sensed since the jamming signals vary from about blanking level to about peak white level. 
     It turns out that it may be possible to modify the scrambled signal such that the cable black box substantially senses a modulated or position modulated signal regardless of adjustments.  FIG. 8A  illustrates a previously scrambled video signal with sync modulation. However, an end of line edge  106  delivers a stable edge for the cable black box when it is adjusted for sensing above blanking level, even though an erroneous clamp pulse (ECP) signal has its leading edge  108  modulated. As illustrated in  FIG. 8B , if a signal  107  is added by edge fill and/or insertion, then a blanking sensing level S2 still will not supply a defeating position modulated signal to the cable black box because of the fact that the leading edge of the signal  107  and the trailing edge of an erroneous clamp pulse (ECP)  109  still are stable and detectable by the black box even though the edges  106  and  108  are modulated. 
       FIG. 9A  illustrates a modification of  FIG. 8B  which overcomes the problems of  FIG. 8B  in that an edge fill signal  110  and/or an ECP signal  116  now include a form of amplitude modulation. That is, in  FIG. 9A , although a leading edge  112  of the signal  110  and a trailing edge  120  of signal  116  are fixed, the trailing edge  114  is position modulated and the edge fill signal  110  and the ECP signal  116  are amplitude modulated so that the stable edge  112  increases and decreases with time, i.e., periodically drops below the black box slice level S2, thereby causing an unstable edge and enhanced concealment. The modulation of the edge fill and ECP signals can be tied together or can each be modulated at a respective rate. A further, even more effective embodiment is shown in  FIG. 9B  where both edges of the edge fill signal  110  are position modulated along with the amplitude modulation. It has been found with some illegal cable decoders, that more effectiveness is achieved by modulating the edge fill signal  110 . Further, turning on and off (or modulating) the edge fill signal and/or the ECP signal (as for example designated by numerals  110 ,  112 ,  114  and  116 ,  118 ,  120  in FIGS.  9 A and  9 B), causes the illegal decoder to generate an even more unviewable picture. Modulating the edge fill signal can be in the form of pulse width, pulse amplitude, pulse coding and/or frequency transformations and/or frequency modulation techniques. 
     The fact that some of these decoders may also differentiate or high pass filter the video signal is illustrated for example in the circuit of FIG.  9 C. As a result of high pass filtering, edge  114  in  FIG. 9A , for example, can be a sync locking signal. By turning on and off this edge at an annoying rate (i.e., 500 milliseconds on and 200 milliseconds off), the illegal cable decoder and/or TV set causes a more unviewable picture. 
       FIGS. 9A and 9B  also show modulated erroneous clamp pulse signals (ECP)  116 . By modulating the ECP signal at an annoying rate (i.e., 1.5 Hz), the illegal cable decoder and/or TV set may display a more annoying picture by periodic picture shifts and/or darkening. 
       FIGS. 9A and 9B  also show a preferable finite rise time for the ECP signal leading edge  118  and a fixed trailing edge  120 . This finite rise time is used sometimes to allow the decoder&#39;s chroma circuits to lock on to the position modulated burst (riding on top of the ECP&#39;s amplitude modulated leading edge) without phase lock loop errors. It has been found when the rise time of edge  118  is at least 100 nanoseconds, for example, the decoder will output a stable and substantially error free subcarrier burst signal. 
       FIGS. 10A through 10K  illustrate waveforms that generate the signals as shown in  FIGS. 9A and 9B .  FIG. 10B  shows a starting timing signal, HBI, that is preferably larger than the normal horizontal blanking period (i.e., about 11.3 microseconds). 
       FIG. 10C  is timed off the leading edge of FIG.  10 B. It is varied by a modulating signal such that the trailing edge of  FIG. 10C  is for example from about 100 nanoseconds to about 5.6 microseconds.  FIG. 10C  triggers a timing circuit one shot to generate the signal as seen in FIG.  10 E.  FIG. 10E  is then the not yet modulated version of pulse  110  and edges  112 ,  114  of FIG.  9 B. 
     The yet to be modulated version of pulse  110  and edges  112 ,  114  of  FIG. 9A  are generated by the waveform as seen in  FIG. 10D  which is generated by a varying one shot off the leading edge of signal HBI, FIG.  10 B. The variation of pulse widths of  FIG. 10D  is from about 500 nanoseconds to about 6 microseconds (for example). 
     Gap g ø , ( FIGS. 9A ,  9 B) is designated in FIG.  10 F and is normally a fixed (sometimes varied) pulse which is triggered off the trailing edge of  FIG. 10D  or  10 E. This gap, g ø , is generally very small (i.e., less than 300 nanoseconds). 
     An actual sync modulation signal  122 ,  FIG. 10G , for concealment in unauthorized viewing is generated by a timing circuit from the trailing edge of  FIG. 10F  or  10 E or  10 D. The pulse width of  122  in  FIG. 10G  is typically fixed (although can be also varied) at about 3 to 4 microseconds (for example). In some TV sets displaying a signal that has a horizontal sync width less than about 3 microseconds, the sync modulation is not effective for concealment. 
       FIG. 10H  illustrates another gap signal, g 1 , used by the decoder to establish a video reference level such as blanking level. The signal g 1  is triggered off the trailing edge of signal  122  and has a duration of about 500 nanoseconds to 2 microseconds. A duration of about 1.2 microseconds is typical for signal g 1 , although other durations can be used for g 1 . 
     A burst gate signal shown in  FIG. 10I  is used to reinsert color burst as shown in  FIGS. 9A and 9B . It is triggered off the trailing edge of signal  122 , the modulated sync signal. 
     The waveform of  FIG. 10J  is timed off the trailing edge of gap pulse g 1  and becomes the basis for the ECP signal  116 . In turn,  FIG. 10K  represents the unprocessed version of the ECP signal  116  as shown in  FIGS. 9A and 9B .  FIG. 110K  shows an ECP signal within the HBI, which is preferable, while  FIG. 10J  shows an ECP signal which may at times be outside the HBI. 
       FIG. 11  illustrates an implementation of the apparatus for generating the improved scrambling signals for illegal cable decoders and/or TV sets. Thus  FIG. 11  is an example of an apparatus that produces signals similar to those shown in  FIGS. 9A and 9B . 
     To generate the improved scrambling signal, the horizontal blanking signal HBI as described previously and shown in  FIG. 10   b  is used as a “master” timing signal. A one shot timing circuit OS  124  triggers off the leading edge of the HBI to generate a signal as shown in FIG.  9 A. the OS  124  output pulse width is varied by a control voltage, Vcont 1  which determines the scrambling pattern as displayed on the TV through the illegal cable decoder and/or just through the TV set. It was found by experimentation that a frequency in the range of 450 HZ to 700 HZ (for example) provides the maximum concealment. For instance, in NTSC, the preferred frequency of Vcont 1  is about 603 Hz with a variation of about 5.5 microsecond. It should be noted that the variation of OS  124  can be larger (varied from about 500 nano-seconds to 7 microseconds) given a longer duration of HBI, for example, which may cause a slight loss in active video in the horizontal direction for the authorized decoded output. 
     The output of OS  124  is fed to a modulator  126  which is controlled by a signal Vmod 1 . The output of modulator  126  is then preferably an amplitude modulated edge fill signal that is fed to an input of a summing amplifier circuit  128 . 
     The gap signal g ø  of previous mention is generated by a OS  130  which is triggered by the trailing edge output of OS  124 . A new (modulated) sync signal ( 122  of FIG.  10 G), is generated by a OS  132  which is fed to an input of the summing amplifier circuit  128  and is triggered by the trailing edge of gap pulse g ø . The trailing edge of signal  122  triggers a OS  134  to generate the gap signal g 1  of previous mention. Signal  122  also triggers a OS  136  for a burst gate signal which in turn controls a burst gate switch  138 . The output of burst gate switch  138  is regenerated color burst for a signal such as shown in  FIGS. 9A and 9B  and is fed to another input of the summing amplifier circuit  128 . A color subcarrier signal is regenerated by way of a chroma phase lock loop circuit or equivalent (not shown) and is fed to the input of the burst gate switch  138 . 
     A OS  140  generates the ECP signal  116  ( FIGS. 9A ,  9 B,  10 J) by triggering off the trailing edge of gap g 1 . The output of OS  140  is fed to an AND gate  142 . The other input of AND gate  142  is the HBI signal and the output of ECPLIM is then a limited pulse width ECP signal which in turn is fed to another modulator circuit  144  with an optional filter for finite ECP rise and/or fall time. Modulator  144  is controlled by a signal Vmod 2  to preferably amplitude modulate the ECPLIM signal. The output of modulator  144  is fed to yet another input of amplifier circuit  128 . 
     The HBI signal controls a switch  146  to insert in the “expanded horizontal blanking interval” during at least a portion of the active field, the modulated edge fill, modulated sync, new burst, and modulated ECP signal as shown in FIG.  9 A. The output of switch  146  is amplified by an amplifier circuit  148  whose output is fed to an RF modulator in the cable system (not shown) for example to transmit the improved scrambled signal for better concealment in TV sets and/or illegal cable decoders. 
     To generate a signal in which the edge fill signal is position modulated such as shown in  FIG. 9B , the OS  124  is replaced with a OS  150  and a control voltage Vcont along with a OS  152 , as illustrated in the  FIG. 11  via phantom lines. 
       FIG. 9C  depicts an example of the type of high pass filter or differentiator circuit that may be used in illegal cable decoders to sense edges of the video signal. These edges can provide just enough horizontal and/or vertical rate signals for the illegal cable decoder to lock up to provide unauthorized viewing. The illegal cable decoder however can be “fooled” into sensing the wrong vertical rate signal if the parts of the video signal are modified as shown in FIG.  12 . 
     By providing a gap signal, g 8 , as shown in  FIGS. 12A and 12B , a “fake” vertical signal is produced in conjunction with an amplitude modulated fake broad(vertical) pulse signal,  156 . Because signal  156  moves up and down (i.e., from −10 IRE to +100IRE in NTSC for example), a differentiated version of the waveforms of  FIGS. 12A-C  results in a waveform illustrated in FIG.  12 D. Note in  FIG. 12D , the larger differentiated “vertical sync” signals  156 ′ are amplitude modulated. As a result, the illegal cable decoder will experience sporadic vertical locking. The signals as designated in  FIGS. 12A-C  are preferably in the vertical blanking interval vicinity (and can move around or vary in number of lines) with preferably, the real vertical syncs removed and replaced as illustrated at the output of FIG.  4 . For instance, signals of  FIGS. 12A-C  can be inserted in place of the control signal V 14  in FIG.  4 . For simplicity only one video line is shown with the modification described above, whereas other lines can be modified. 
     Alternatively, a few lines of the waveforms shown in  FIGS. 12A-C  can be inserted after amplifier circuit  80  of FIG.  4 . The gap(s) g 8 , plays an important role since it mimics the serrated vertical syncs of a normal vertical sync signal. The locations of g 8  are important as to cause the illegal decoder to lock up incorrectly.  FIG. 12  is an example of g 8  locations, whereby it should be noted that the number and locations of gaps g 8  are not limited to those shown in  FIGS. 12A-B . The signals  156  of  FIGS. 12A-C  can also extend to − 40  IRE as long as the authorized decoder will still decode correctly. Also the gap g 8  may be varied in width, or may be eliminated in selected situations. 
     Before an explanation of  FIG. 13  is discussed, it should be noted that in  FIG. 4 , not all the TV lines of the vertical blanking intervals need to be filled with a varying pedestal voltage (as shown in FIGS.  12 A-C). With needed data lines, it has been found that a varying pedestal voltage (i.e. at a rate of 9.4 HZ from −10 IRE to +100 IRE) inserted in some of the lines in the vertical blanking interval (VBI) and its vicinity is sufficient to cause problems for the illegal decoder (and/or TV set). The key is to fill in the varying voltage or pedestal into those unused, blanked and/or static signal lines in the VBI and its vicinity. 
       FIG. 13  illustrates an implementation to generate, for example, the waveforms as shown in  FIGS. 12A-C . For effective concealment the circuit of  FIG. 13  can be used in any combination with the circuit of FIG.  11  and/or FIG.  4 . In  FIG. 13 , video is fed to a timing circuit  160 , one output of which defines selected lines around the VBI. Another output of circuit  160  defines the active horizontal line. AND gates  162 ,  163  use these two signals to control or to insert the modified signal as described for example in  FIGS. 12A-C . The selected lines signal from circuit  160  is fed to a timing circuit OS  166 , which is provided with a control signal Vcont 2  which varies the pulse width of the OS  166 . Generally OS circuit  166  applies pulse width modulation on the selected lines signal, the duration of which may be for example 635.5 microseconds or 10 lines of duration, or a range of varying line durations. The output of OS circuit  166  may vary between 31 microseconds (a half line) to 635.5 microseconds (ten lines). 
     The output of timing circuit  160  also outputs the gap signal g 8 . An invertor circuit  168  inverts the logic level of g 8  to blank the output of the AND gate  162  during the g 8  signal. The output of AND gate  162  then is a logic high version of the signal  156  in  FIGS. 12A-B . A modulator circuit  170  preferably amplitude modulates the output of AND gate  162  via control signal Vcont 3 . The modulator circuit  170  can be other types of modulators such as pulse width, position, PCM, FM, and the like modulators. By using summing resistors RS  1  and RS 2 , the varying signal  156  controlled by the signal Vcont is summed with the g 8  signal into an input of a switch  172 . The output of switch  172  is amplified by circuit  174  which generates a signal as shown in  FIGS. 12A-C  with optional pulse width modulation and/or truncation of g 8  and/or signals  156  in particular selected lines. 
     It has been found in certain circumstances, that the ECP signal will restore the horizontal concealment caused by the positional sync modulation. The following concealment summary describes the reaction of a TV set not including the illegal cable decoder. 
     With no vertical sync and positional horizontal syncs, edge fill with an ECP signal shows more (horizontal tearing) concealment than without an ECP signal. If the edge fill is turned completely off, there is no difference in concealment whether ECP is on or off. In addition, concealment is less. 
     With vertical sync pulses turned on 50% of the time and at different locations (as defined as vertical mod 1 ) from one field to the next, there is little change in concealment whether ECP or edge fill is turned on or off. If the vertical mod 1  has sporadic blanking on the vertical sync pulses, then it is found that the best concealment is achieved when edge fill is turned off and ECP turned on (although turning off ECP caused a minor drop in concealment). If edge fill is turned on, then the concealment is worse whether ECP is on or off. 
     For best concealment in illegal cable decoders, it should be noted that the vertical sync pulses are blanked. Thus the best combination (in some cases) consists of edge fill with ECP. 
     Although the invention has been described herein relative to specific embodiments, various additional features and advantages will be apparent from the description and drawings, and thus the scope of the invention is defined by the following claims and their equivalents.