Abstract:
An improved method and apparatus for maintaining concealment for a scrambled signal when frequency pre-emphasis is used to defeat the scrambling. The pre-emphasis may be synthesized with high pass or peaking circuitry. More commonly however the pre-emphasis is available in television sets with a fine tuning control. By adjusting the fine tuning control to cause purposely mistuning off center, a peaking effect is generated which is used to counter the scrambled signal. The application discloses one embodiment which uses de-emphasis to counter the peaking effect. In another embodiment, signals added in the vicinity of the horizontal blanking interval causes the peaking effect to enhance these added signals over stable edges of the video signal. Since these added signals are position modulated for example, the television&#39;s sync circuits and horizontal oscillator circuits will cause scan circuits to generate position modulation. Thus adding a specific type of signal causes the peaking circuit to enlarge the added signals more than the other parts of the video signal for synchronization.

Description:
REFERENCE TO PROVISIONAL APPLICATIONS 
     This application claims priority to U.S. provisional applications Ser. No. 60/093,694 filed Jul. 22,1998 and Ser. No. 60/108,182 filed Nov. 11, 1998. 
     CROSS REFERENCE TO RELATED APPLICATIONS 
     This invention is related to International Application PCT/US98/05163 filed on Mar. 17, 1998, U.S. patent application Ser. No. 09/212,236 filed on Dec. 17, 1997, by Quan; and U.S. Provisional Application filed Feb. 26, 1998, now U.S. patent application Ser. No. 09/233,99,236 filed on Jan. 20, 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 scrambling signals that are transmitted or sent over cable and, in particular to a method and apparatus for overcoming the defeat of video signal scrambling processes caused by fine mistuning of a tuner circuit in a television set. 
     BACKGROUND OF INVENTION 
     With the fine tuning feature present in many television sets and VCRs, many current television scrambling systems are vulnerable to this feature. By fine tuning (mistuning) in just the correct way, a viewable picture is possible from a scrambled video signal. Such scrambled video signals, for example, may come from sync suppression scrambling systems and/or from video signals where the horizontal sync pulses are position and/or edge modulated. 
     The fine tuning feature of a television timer shifts the tuner&#39;s local oscillator to shift the video spectrum within the tuner&#39;s intermediate frequency (IF) bandpass filter. See for example, FIGS. 1A,  2 A and  3 A- 3 E. If the fine tuning is set to be slightly off center (mistuned), the mixed down video in the IF bandpass (FIGS. 3C,  3 E) will not be optimal and will exhibit some middle to high frequency emphasis at the tuner&#39;s demodulator output (FIG.  4 ). As a result, the video signal will have leading and/or trailing edge emphasis or spikes in the time domain. The television&#39;s (TV) sync separator will sense the over emphasized negative or trailing edges as “sync” signals. Generally, the end of line picture information has some of the greatest negative edge information and becomes a sync signal when fine mistuned. As a result, a viewable picture is achieved on the TV set even though the video signal used sync suppression scrambling. Under correctly tuned conditions, the TV set would show a concealed and unviewable picture. The use of frequency equalizing the scrambled video, for example via fine mistuning, not only works to defeat the scrambling feature of sync suppression systems, but also to defeat those scrambling systems with position or edge modulated horizontal syncs. 
     SUMMARY OF THE INVENTION 
     Therefore there is a need for a countermeasure to video frequency equalization via use for example of the television&#39;s fine tuning control, such that various existing signal scrambling systems continue to provide concealed or unviewable signals. 
     The present method for maintaining concealment provided by sync suppression and sync modulation systems, under fine mistuned circumstances in a TV set, is to deemphasize the video frequency response in the scrambled signal prior to the modulator. At the descrambler end, a pre-emphasis in video frequency response is done to obtain an overall flat frequency response from transmitter to descrambled video output. 
     Yet another method that identifies that the end of line program content is the source for a viewable picture during fine tuning (mistuning), changes the fall time of the negative edge of video near the end of the television line. 
     Where sync modulation exists, there are other methods available to maintain concealment when the television set is fine mistuned to defeat this type of scrambling. One method that is prior art, is to have the trailing edge of video follow the sync modulation. 
     In this invention, there are several other ways to improve on the concealment. One way is to make the last 2 microseconds of the active video line close to a peak white level and then modulate the falling edge of this peak white level to follow the sync modulation. This peak white level guarantees that the trailing edge of the end of video line will be picked up by the fine tuning. A huge position modulated negative spike caused by fine tuning (mistuning) will be picked up as a sync signal and will maintain concealment via the position modulation. 
     Yet another way to maintain concealment of a sync modulated scrambling mode when fine mistuning is used to offset it, is to use a combination of peak white level and a waveform that follows the sync modulation during the last 2 microseconds of the end of the active video line. Upon addition of a waveform typically at about 500 Khz to 2 Mz, the waveform becomes enhanced during the fine tuning and thus appears as sync signals to the TV set. Since this waveform is also position modulated, it will cause the TV set to deliver a concealed picture. In short, under normal or correct fine tuning, the sync modulation causes the concealment of the video signal on a TV set. When the fine tuning is incorrect, the combination of the peak white level and/or waveform that is position modulated then causes the TV set to still deliver a concealed picture. 
     Still a further alternative embodiment includes various forms of vertical sync suppression and insertion, particularly in a sporadic manner. Thus, reinsertion of vertical sync pulses, although not necessarily standard vertical sync signals, along with the horizontal concealment techniques of previous mention provides enhanced signal concealment, particularly when using non-standard and/or sporadic vertical sync pulses in the VBI period. To this end, one technique of the invention removes some or all original vertical broad sync pulses and inserts a VBI with new vertical sync pulses of non-standard vertical sync locations, line fill signals and/or blanking or other signal voltages, in a sporadic or periodic manner. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A illustrates a typical baseband frequency response from a TV tuner with the fine tuning control set at the normal position. 
     FIG. 1B illustrates a baseband frequency response from the TV tuner with the fine tuning control set at a mistuned position to cancel the effects of scrambling. 
     FIG. 2A illustrates the typical output video waveform when the fine tuning is set for normal or optimal. FIG. 2A is a result of the frequency response shown in FIG.  1 A. 
     FIG. 2B illustrates the overshoot response of a video signal due to the incorrect fine tuning that cancels the effects of video scrambling. FIG. 2B is a result of the frequency response shown in FIG.  1 B. 
     FIG. 2C illustrates a typical waveform for a sync modulated scrambled signal with fine tuning set correctly. 
     FIG. 2D illustrates a typical waveform for a sync modulated scrambled signal with the fine tuning (mistuning) set to cancel the scrambling effect by causing excessive overshoot response. 
     FIG. 2E illustrates a typical waveform for a sync suppression scrambling signal at the TV tuner&#39;s baseband video output when the fine tuning is set to normal. 
     FIG. 2F shows the sync suppression scrambling signal with excessive overshoots caused by incorrectly fine tuning the TV tuner to cancel the scrambling effects. 
     FIG. 3A illustrates the Radio Frequency (RF) spectrum of a TV channel. 
     FIG. 3B illustrates the spectrum of the Intermediate Frequency (IF) portion of the tuner due to the RF input of FIG.  3 A. 
     FIG. 3C illustrates a shift in the IF spectrum of FIG. 3B due to incorrect fine tuning to cancel the video scrambling effects. 
     FIG. 3D illustrates the IF bandpass filter frequency response. 
     FIG. 3E illustrates the IF frequency response of an incorrectly fine tuned TV signal. 
     FIG. 4 illustrates a resultant demodulated video frequency response from FIG.  3 E. Note the boosted middle and high frequencies. 
     FIG. 5A illustrates a block diagram of an embodiment of this invention using de-emphasis circuitry and illustrating pre-emphasis caused by fine mistuning. 
     FIG. 5B illustrates a band reject filter commensurate with a de-emphasis network of the invention. 
     FIG. 5C illustrates a band pass filter capable of generating pre-emphasis such as caused by fine mistuning. 
     FIG. 5D illustrates the relative frequency responses of both de-emphasis and preemphasis filters. 
     FIG. 6A illustrates another de-emphasis filter circuit of the invention. 
     FIG. 6B illustrates another pre-emphasis filter circuit. 
     FIG. 6C illustrates the frequency responses of circuits shown in FIG.  6 A and FIG.  6 B. 
     FIG. 6D illustrates the video waveform result when using a circuit such as illustrated in FIG. 6A for a modulated sync ( 6 A( a )) and a sync suppression ( 6 A( b )) scrambling process, respectively. 
     FIG. 6E illustrates the video waveform resulting from incorrectly fine tuning the TV for a modulated sync ( 6 E( a )) and a sync suppression ( 6 E( b )) scrambling process, respectively. FIG. 6E can also be the resulting waveform if a pre-emphasis network is used in the decoder when the TV set is correctly fine tuned. 
     FIG. 7A illustrates a block diagram of the invention for lengthening the fall time and/or rise time of the end of video by using an amplifier that has very slow negative or positive slew rate, which should cancel the overshoot response of an incorrectly fine tuned TV during the falling edge of the video. 
     FIG. 7B is a waveform illustrating the effect of the circuit in FIG.  7 A. 
     FIG. 8A illustrates a prior art waveform with sync modulation that is somewhat resistant to incorrect fine tuning. 
     FIG. 8B illustrates an improved sync modulation scrambling waveform generated by inserting a peak white signal near the end of the TV line in accordance with the invention. 
     FIG. 8C illustrates an improvement over the results shown in FIG.  8 A and FIG. 8B, generated in accordance with the invention by adding a new position modulated waveform WAV 1  as shown with a peak white signal. Optional signals ECP and WAV 2  are also shown. 
     FIG. 8D illustrates a variation of FIG. 8C generated by sharpening and/or pre-emphasizing the edges of the modulated peak white signal and WAV 1  and the edges of the modulated sync, so that an incorrectly tuned TV uses these as sync signals, thereby preserving concealment. Optional signals ECP and WAV 2  are also shown. 
     FIG. 9 illustrates a circuit of the present invention that generates the waveform WAV 1  as seen in FIGS. 8C and 8D, along with edge fill and controlled fall and/or rise times in the HBI (horizontal blanking interval) via a slew limit amplifier, and also illustrates circuits that generate the optional waveforms ECP and WAV 2 . 
     FIGS. 9A-9G are waveforms illustrating the signals generated at various points along the circuit of FIG.  9 . 
     FIG. 10 illustrates a horizontal concealment signal in accordance with the invention with a modulated edge fill pulse (MEFP) and/or modulated erroneous clamp pulse (MECP) signal. This modulation may be amplitude, pulse width and/or frequency, and the like. 
     FIG. 11 illustrates a block diagram of the invention for providing a sporadic vertical sync modification. 
     FIG. 12 illustrates another block diagram of the invention in which new sporadic vertical syncs arc multiplexed with line fill signals. 
     FIG. 13 illustrates another block diagram of the invention for inserting the nonstandard vertical sync signal of, for example, FIG. 10, while alternately inserting line fill signals. 
     FIG. 14A is a waveform illustrating standard vertical syncs in a video signal. 
     FIGS. 14B-14F are waveforms illustrating the various vertical sync signals and line fill modifications of the invention that may be used with the signal illustrated in FIG. 10 for an effective video concealment signal in the presence of fine mistuning. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A main intent of this invention to overcome the neutralizing effects that a pre-emphasis circuit, such as a fine mistuned filter depicted for example in FIGS  5 C and  6 B, has on a scrambled signal. See for example FIGS. 1B,  2 B,  2 D,  2 F,  3 C,  3 E and  4  for responses and waveforms generated by fine mistuning processes. The scrambled signal such as illustrated in FIGS. 2C,  2 E and  8 A, may be the result of horizontal sync modulation and/or sync suppression scrambling processes. In some sync suppression systems, controlled rise and/or fall times in the HBI, for example, can offset the neutralizing effects of the television&#39;s tuner being fine mistuned. The controlled rise and/or fall times may be realized by a slew rate amplifier such as in FIG. 7A, which generates the waveform described in FIG.  7 B. In FIG. 7A the fall and rise times are controlled via a signal IE with CSLEWNEG and a signal IE 2  with CSLEWPOS respectively. Controlled rise and/or fall times may also be realized by using de-emphasis circuits such as in FIG.  5 B and FIG.  6 A. The resulting transient responses are shown in FIGS. 5D and 6C. 
     FIG. 6E shows a resultant waveform after fine tuning (mistuning) has been applied to cause a pre-emphasis effect. As seen in FIG. 6E, the video signal has little overshoot or preshoot and signals S 1 A and S 2 A are the resulting normal modulated sync and suppressed sync scrambling signals. In the case of fine tuning (mistuning) to the extreme to “decode” a scrambled signal with horizontal overlays for instance, the preemphasis curve can exceed +6 dB per octave. 
     In some cases, a normal video signal with flat frequency response to about 4 Mhz will show a +12 dB per octave slope of pre-emphasis. As a result the video waveform will have both overshoots and preshoots similar to video aperture correction circuits. As a result substantial de-emphasis may be required. However substantial de-emphasis can mean a loss of overall signal to noise ratio at the decoder output. Therefore, to preserve signal to noise ratio, by not necessarily using de-emphasis, it is possible to add extra signals to preserve the scrambling effect even when using “extreme” fine tuning. These extra signals do not cause extra concealment in a normally tuned set, but cause a mistuned set to “scramble” or maintain at least some concealment. Extra signals such as waveforms WAV 1  and WAV 2  are illustrated in FIG.  8 C. It is an object for extra signals WAV 1  and/or WAV 2  to follow, in general, the position modulation of the horizontal sync. When fine mistuning is used to cause pre-emphasis, the position modulated extra signal such as WAV 1  will be over emphasized as depicted in dashed line and cause the television set&#39;s horizontal oscillator to follow the WAV 1 &#39;s position modulation. Note that the number of cycles in WAV 1  and/or WAV 2  can be anywhere from one half to many. As a result, a concealed picture will be displayed. 
     It has also been found that extreme pre-emphasis caused by mistuning of the tine tuning, or other means (circuitry) that causes preshoots of the video signal, can have a neutralizing effect on the scrambled signal. As previously mentioned, a peak white signal near the end of the active line with a track and hold edge fill is beneficial. However it is sometimes better to track and hold the last few or so pixels (luma pixels for example) instead of tracking and holding a peak white level signal. The reason is that the peak white level signal has a stable leading edge that acts like a stable horizontal sync signal when pre-emphasized with preshoots. It may then be necessary to modulate the leading edge of the peak white level signal to insure concealment with fine mistuned television sets (see FIG.  8 B). 
     To maintain concealment in a frequency pre-emphasized environment, a combination of de-emphasis and an apparatus as shown in FIG. 9 may be used. FIG. 9 illustrates an edge fill circuit for the last active pixels, a slew limit amplifier for generating controlled rise and fall times, a position modulated waveform circuit (WAV 1 ), a position modulated sync circuit (NEW SYNC), an erroneous clamp pulse (ECP) (position modulated) circuit, and another position modulated waveform circuit (WAV 2 ). It should be noted that the WAV 1 , WAV 2 , ECP, and NEW SYNC signals can also be amplitude, frequency, position and/or pulse width modulated. 
     Referring to FIG. 9, the video input which may be scrambled or unscrambled, is fed to a horizontal blanking interval (hereinafter HBI) blanking switch  80  responsive to an HBI blanking control. The video input is also fed to a sample, or track and hold, circuit known as “edge fill” circuit  82 . The output of blanking switch  80  has about 12 to 16 microseconds blanked in the HBI period. The leading edge of HBI blanking control is fed to a variable one shot timing circuit  84  which provides an output of EFL, a position modulated signal that has for example about an 8 microsecond positional shift within the HBI vicinity. The EFL signal is used to control edge fill circuit  82  so the last luma pixels of the television line are filled into the HBI as the EFL signal is position modulated. The output of edge fill circuit  82  is coupled to one input of a switch  86  and to a slew rate limit amplifier  88 , whose output in turn is coupled to the other input of the switch  86 . Switch  86  is controlled by a signal SLW CONT which inserts slower rise and fall times into the HBI vicinity. The slew rate circuitry may be used to control the rise and fall times within the HBI where the edge fill signal is not used. The output of switch  86 , which is fed to an input of a summing circuit  90 , then is a track and hold signal corresponding to the last pixels, and/or to slow rise and/or fall times of the video signal during the HBI vicinity. The EFL signal also supplies a one shot timing circuit  92 , which is set normally for a short duration (i.e. less than 1 microsecond) to set up an optional gap between the edge fill signal and the beginning of WAV 1 . The output of circuit  92  (FIG. 9A) is supplied to another one shot timing circuit  94 , which sets the start and stop points on a WAV 1  oscillator circuit  96  via a gate signal. The output of circuit  96  (FIG.9B) is then a position modulated wave front signal WAVE corresponding to signal EFL and is coupled to an input of the summing circuit  90 . 
     To generate a position modulated NEW SYNC signal after the WAV 1  signal, one shot circuits  98  and  100  are used. Circuit  98  sets up an optional gap between the end of WAV 1  signal and the beginning of NEW SYNC signal. The circuit  100  sets the width (i.e. about 2 microseconds) of NEW SYNC signal. The output of circuit  100  is supplied to an inverting amplifier  102 , whose output (FIG. 9C) is supplied to another input of the summing circuit  90 . It should be noted that amplifier  102  may contain a low pass filter to roll off the transient rise and/or fall times of NEW SYNC. Thus the output of amplifier  102  may instead have a rolled off (transient or frequency) response of the NEW SYNC signal (for example, see the sync signal of FIG.  6 D. 
     A regenerated burst signal is also position modulated and is derived by triggering off the trailing edge of the NEW SYNC signal via a one shot circuit  104  which sets the burst envelope width. An AND gate  106  gates through a color subcarrier frequency signal supplied thereto, to supply a new color burst signal (FIG. 9D) into summing circuit  90 . 
     Optional waveforms such as an erroneous clamp pulse and/or another wave packet similar to WAV 1  (FIGS. 8C,  8 D) can also be added after the NEW SYNC signal. These optional waveforms will also be emphasized by the fine mistuning of previous mention, or equivalent effects. Since these optional waveforms are also position modulated, the television set may then display a more concealed picture. Thus, the output of the one shot circuit  100  is coupled to a one shot circuit  108  which sets up an optional gap between the trailing edge of NEW SYNC and the leading edge of an erroneous clamp pulse (ECP) signal. The width of ECP signal is set by a one shot timing circuit  110 . Ideally if a WAV 2  signal (see below) is not used, the ECP signal stretches from the trailing edge of NEW SYNC to the end of the HBI. Under these conditions, ECP signal can have a pulse width as large as 8 microseconds or more (after NEW SYNC) which can be very useful in creating a darkened display. The output of timing circuit  110  is fed to an amplifier  112  whose output (FIG. 9E) is coupled to another input of the summing circuit  90 . 
     The WAV 2  signal is another wave form similar to WAV 1  which follows the NEW SYNC or ECP signal. It is generated by a gated oscillator  114 . The gate width is determined by a one shot timing circuit  116  (FIG. 9 F). The optional gap between the start of WAV 2  and NEW SYNC is determined by a one shot timing circuit  118 . The output (FIG. 9G) of the WAV 2  oscillator  114  is then coupled to still another input of the summing circuit  90 . 
     The output of summing circuit  90  is coupled to an output amplifier  120 . An example of the output signal supplied via the amplifier  120  is illustrated in FIG.  8 C. 
     It should be known that modifying, shifting or varying the carrier of the modulator as illustrated in FIG. 5A for example, is another technique of the invention for maintaining concealment of the scrambled signal when fine mistuning is attempted. The reason is that the person using the fine tuning control will have to continuously remistune mistune the fine tuning of the television set. However, the modulator&#39;s carrier frequency is varied in a random fashion. Thus it is very difficult to re-mistune the fine tuning in the random fashion as means to cancel the concealment effect of the scrambled signals. The random frequency variation of the modulator carrier frequency can be of the order of plus to minus 300 kHz, for example. Of course, the rate of frequency change should be kept low (i.e. a 600 kHz shift over the period of 2 seconds), for example to allow the TV set to be viewed with minimum artifacts. 
     As previously mentioned, in some cases television receivers with fine tuning allow improved viewing of scrambled signals. However, it was found that a combination of horizontal overlay signals such as those illustrated in FIG. 10, and modified vertical sync insertion and/or deletion, re-established concealment in accordance with the invention. The use of modified, random or non-random vertical sync signals in the VBI vicinity can also be used to enhance scrambling in general. 
     To this end, FIG. 10, illustrates an example of a scrambled signal that causes improved horizontal concealment. It consists of a single or double edge modulated sync, MODSYNC, a modulated edge fill signal, MEFP, and a modulated erroneous clamp pulse signal, MECP (for darkening and or horizontal concealment). For a typical application, MEFP can be amplitude modulated. MECP can also be amplitude modulated. The modulation frequencies (and/or phase) can be the same or different for MEFP and MECP. It was found that MEFP and MECP were amplitude modulated in the frequency range of 10 Hz to 20 Hz, for example, there was very intense flickering that discouraged viewing. Thus, an object of the invention is to cause viewer discouragement, in this instance by flickering the scrambled signal to conceal the program video. 
     At the same time if MDSYNC is position (or pulse width) modulated for example at about 601 Hz in a 60 Hz field frequency system, good horizontal concealment is provided in a normally tuned set. 
     However, with some other television receivers, whether mistuned or not, it was found that a signal such as in FIG. 10, if accompanied with vertical sync suppression (i.e. substantial reduction in vertical broad sync pulses) causes some reduction in concealment. It also was found that reinsertion of vertical sync pulses, although not necessarily standard vertical sync, provides improved horizontal concealment. For both horizontal and vertical concealment it is preferable that a signal such as that illustrated in FIG. 10 be combined with non-standard and/or sporadic vertical sync pulses in the VBI period. The reason for using non-standard vertical sync pulses, is that use of a consistent or standard vertical sync signal allows the television receiver and/or illegal cable decoder to reduce concealment. 
     One way to create non-standard vertical sync is illustrated in FIG. 11, wherein processed video such as program video with the modifications of FIG. 10 is input to a selector switch  122 . The output of switch  122  contains the horizontal concealment signals of FIG. 10 during much of the active television field plus a vertical blanking interval (VBI) modification. This VBI modification, for example, removes all of the original vertical broad sync pulses, and inserts, in a sporadic or periodic manner, a VBI with new vertical sync pulses of non-standard vertical sync locations, line fill signals, and/or blanking level signals, or other signal voltages. This modification can switch via the switch  122  between new vertical sync pulses of varying locations and a line fill signal (i.e. a varying signal from about blanking to about white level). From time to time, the VBI may contain a third signal such as a blanking signal or a voltage signal. FIG. 11 then illustrates a manner in which the video signal is modified by the switch  122  which in turn is controlled by a timing circuit  124  driven by an insertion generator source  126 . The output of switch  122  thereby causes a television receiver tuned normally or not normally to have at least vertical instability and/or horizontal concealment. 
     FIG. 12 illustrates yet another example of generating a television scrambling signal resistant to the fine mistuning process (but can be used with correctly tuned TV sets as well). Under normally tuned sets, an output  128  provides both vertical and horizontal concealment. Here again the vertical sync pulses are made non-standard so that vertical instability occurs when fine mistuning is attempted by an unauthorized viewer. Processed or scrambled video containing the modifications shown for example in FIG. 10, along with video line position modulation, are supplied to FIG. 12 via an input  130 . Any vertical sync pulses are reduced and/or eliminated by a vertical sync blanking circuit  132 , which provides to a summing circuit  134  a version of the signal on input  130  but without vertical sync pulses. A timing circuit  136  coupled to input  130  adds nonstandard sync in various locations near or in the VBI and supplies the signal to the summing circuit  134 . The output of circuit  134  is supplied to a switch  138  via a resistor. A second timing circuit  140  coupled to input  130  controls the switch  138  in a sporadic or periodic manner so as to blank out the new vertical sync pulses at preferably random times. 
     That is, some times vertical sync pulses of one location pass through the switch  138  while at other times vertical sync pulses of another location are blanked. At times, vertical sync pulse of all locations may be blanked by switch  138 . Whenever any of the new vertical (non-standard) sync pulses are blanked, it is preferable but not necessary to add and/or insert a signal in the locations of blanked new vertical sync pulses. This is illustrated via a line fill generator  142  and a logic AND gate  144 . The output of the AND gate  144  is a signal that is logic high corresponding to those lines that are blanked by switch  138 , and which is supplied to a modulator  146  (i.e. amplitude, pulse width, frequency and the like). In one example, the output of modulator  146  is an amplitude modulated signal which varies from about blanking level to about white level. The selectively modulated signal is supplied to a summing circuit  148 . 
     The output of modulator  146  is also referred to as a line fill signal which fills in the VBI and its vicinity with generally non-blanking level signals. Such a line fill signal becomes important in some cases for resistance to certain television receivers and/or illegal cable decoders. The line fill signal also may be varied from about sync level to about white level with the option of at least one serration in each line of the line fill signal. 
     In FIG. 12, the summing circuit  148  provides the output  128  which comprises a scrambled signal that contains video position modulation and various signals as shown in FIG.  10 . The output  128  also includes, for example, the sporadic vertical sync pulses of various locations and line fill signals of previous mention. It should be noted that the vertical sync pulses at the output  128  may also have been modulated by amplitude, pulse width and the like, and/or may also contain serrations. 
     FIG. 13 is a simplified block diagram illustrating an insertion switch  150  receiving a scrambled video input with VBI line fill signals (LF) and non-standard vertical syncs (VS 1  and VS 2 ) along with signals such as those in FIG.  10 . The other input of switch  150  is the modulated line fill signals, LF 1  and LF 2 . The switch  150  is controlled with a logic AND gate  152 , a timing circuit  154  and a generator  156  such that the output of the switch has properties similar to those described on output  128  in FIG.  12 . Timing circuit  154  provides a logic high for the television line locations of VS 1  and VS 2 . Generator circuit  156  is used to gate through any combination of VS 1  and VS 2 . The switch  150  switches in any combination of LF 1  and LF 2  whenever any combination of VS 1  and VS 2  is not passed. The line locations of LF 1  and VS 1  are for example substantially the same, and the line locations of LF 2  and VS 2  also are for example substantially the same. 
     FIGS. 14B to  14 F show examples of the “sporadic” vertical sync pulses of previous discussion. FIG. 14A illustrates a video signal that has normal vertical sync signals. FIG. 14B illustrates a video signal with the vertical sync pulses removed. 
     FIG. 14C illustrates line fill signals, LF, added or inserted to the non-standard vertical sync signals, VS 1  and VS 2 . See FIG. 14C color field II. LF signals can also comprise data and/or test signals along with a modulated signal. 
     FIG. 14D illustrates a situation where non-standard VS 1  and VS 2  are replaced with line fill signals, LF 1  (pre) and LF 2  (post). FIG. 14E illustrates a situation where only VS 1  reappears in color field II. FIG. 14F illustrates VS 1  replaced with a line fill signal in color field II while VS 2  reappears in color field III. 
     For this invention, any combination of the examples shown in FIGS. 14B through 14F over time periods, can generate the desired effect of overcoming the scrambling defeating effects of fine mistuning.