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Technical Notes:
CABLE FAQ #2 ( Updated )
The ownership of a signal descrambler does NOT give the owner the automatic right to decode or view any scrambled signals without authorization from the corresponding company or individual. Use of such a device without permission may be in violation of state and/or federal laws. The information contained herein is intended to serve as a technical aid to those person seeking information on various scrambling technologies. No liability is assumed for the use or misuse of this information.
Traps(Traps/Addressable Taps)
A cable system may not be scrambled at all. Some older systems (and many apartment complexes) use traps or filters which actually remove the signals you aren't paying for from your cable. (These are negative traps because they remove the WHOLE signal.) These systems are relatively secure because the traps are often located in locked boxes, and once a service technician finds out they're missing or have been tampered with (by pushing a pin through a coax trap it to change its frequency, for example), it's a pretty solid piece of evidence for prosecution.
Another method is where the head-end ADDS an extraneous signal about 2.5 MHz above the normal visual carrier which causes a tuner to think its receiving a very strong signal--the tuner then adjust the automatic gain control and buries the real signal. If you pay for the service, the cable company adds a positive trap which then REMOVES the extraneous injected signal so it becomes viewable. (This system is very easy to circumvent by building your own notch filter, so it is not very commonly used.)
Advantages to a cable system with this technology is that you don't need a cable box--all your cable-ready TVs, VCRs, etc. will all work beautifully. The disadvantage is that pay-per-view events are not possible, and that every time someone requests a change in service, a technician has to be dispatched to add/remove the traps.
An article for building a tunable notch filter to block data streams sent just above the FM band was in the April 1992 issue of Radio-Electronics (pp. 37-39). Notch filters (as well as kits for them) for other frequencies are frequently advertised in Nuts & Volts magazines as beep filters and the like.
Becoming more and more popular, not only because of the Cable Act of 1992 but also in an effort to stop pirates are addressable taps. Many cable companies will be moving to this technology in the near future, (which they call interdiction). These are devices located at the pole, where your individual cable feed is tapped from the head-end. Similar to addressable converters, they each have a unique ID number and can be turned on/off by a computer at the head-end.
Any stations which you are not paying for are filtered out by electronically switchable traps in the units. (Including the whole signal if you haven't paid your bill or had the service disconnected.) {Several patents have already been issued for various methods of making SURE you don't see a channel you don't pay for.} Again, these almost guarantee an end to piracy and don't have any of the disadvantages of the manual traps.
Plus, they provide a superior signal to those customers paying for service because they no longer need complicated cable boxes or A/B switches -- and they can finally use all of the cable-ready capabilities of the VCR, TV, etc. About the only known attack on this type of system is to splice into a neighbors cable, which again provides plenty of physical evidence for prosecution.
Early Oak (and some very early Pioneer boxes) employed a sine-wave sync suppression system. In this system, the picture would remain vertically stable, but wiggling black bars with white on either side would run down the center of the screen. The lines were caused by a 15,750 Hz sine-wave being injected with the original signal, causing the sync separator in the TV to be unable to detect and separate the sync pulses.
Later, Oak came out with a Vari-Sync model, which also removed a 31,500 Hz sine-wave added to the signal. Oak was one of the first to use extra signals (tags) as a counter-measure for pirate boxes -- in the normal mode, a short burst of a 100 kHz sine-wave (the tag signal) would be sent during the VBI, along with the AM sine-wave reference on the audio carrier and scrambled video. They would then put the AM sine-wave reference signal onto the audio carrier, leave the video alone, and NOT send the tag.
Any box which simply looked for the AM sine-wave reference would effectively scramble the video by adding a sine-wave to the unscrambled video! Real decoders looked for the tag signal and still worked correctly. Other combinations of tag/no tag, scrambled/unscrambled video were also possible.
6 DB IN-BAND SYNC SUPPRESSION Early Jerrold boxes used in-band gated sync suppression. The horizontal blanking interval was suppressed by 6 dB. A 15.734, 31.468 or 94.404 kHz reference signal (conveniently all even multiples of the horizontal sync frequency) was modulated on the sound carrier of the signal, and used to reconstruct the sync pulse.
An article in February 1984 issue of Radio-Electronics explains this somewhat-old technique. Converters which have been known to use this system include the Scientific-Atlanta 8500-321/421, a number of Jerrold systems [see numbering chart], Jerrold SB-#, SB-#-200, SB-#A, RCA KSR53DA, Sylvania 4040 and Magnavox Magna 6400.
A modification to the 6dB sync suppression system, dubbed Tri-mode, allows for 0, 6 and 10 dB suppression of the horizontal sync pulse. The three sync levels can be varied at random ,as fast as once per field, and the data necessary to decode the signal is contained in unused lines during the VBI along with other information in the cable data stream.
See the February 1987 issue of Radio-Electronics for a good article including both theory and schematics, on the Tri-mode system. Converters which have been known to use this system include a number of Jerrold systems [see numbering chart], Jerrold SBD-#A, SBD-#DIC, Jerrold Starcom VI (DP5/DPV models), Regency, Scientific- Atlanta 8550-321 and early Pioneer systems.
Out-Band Sync Suppression
Out-band gated sync systems also exist, such as in early Hamlin converters. In this system, the reference signal is located on an unused channel, usually towards the higher end (channels in the 40's and 50's are common, but never in the low 30's due to potential false signaling.) The signal is comprised of only sync pulse information without any video. Tuning in such a channel will show nothing but a white screen and will usually have no audio.
SSAVI is an acronym for Synchronization Suppression and Active Video Inversion and is most commonly found on Zenith converters. ZTAC is an acronym for Zenith Tiered Addressable Converter. Besides suppressing sync pulses in gated-sync fashion, video inversion is used to yield four scrambling modes (suppressed sync, normal video; suppressed sync, inverted video; normal sync, inverted video; and normal sync, normal video).
The horizontal sync pulses of an SSAVI signal can be absent completely, at the wrong level, or even present, and can be varied on a field-by-field basis. Any decoder for an SSAVI or similar system has to be able to separate a video line into its two basic components-- the control and picture signals. In SSAVI, the horizontal sync is never inverted, even if the picture is.
So a method of inverting the picture without inverting the control section is necessary. This is complicated by the fact that almost every line in an SSAVI signal has no horizontal sync information, making it difficult to perform the separation since the usual reference point, the horizontal sync pulse, is gone.
In the older suppressed-sync system, the sync pulse could be recovered from the gating signal buried in the audio subcarrier, but SSAVI is pilotless. The key to this system relies on the strict timings imposed by the NTSC standard--if you can locate one part of the signal accurately, you can determine where everything else should be mathematically.
Since the cable company is sending a digital data stream---the security and access-rights--during the VBI of the signal, the VBI makes a great place to find a known point in the signal. Obviously if the electronics in the cable box can locate this information, so can electronics outside the cable box!
The only constant in the SSAVI system are the horizontal sync pulses during the VBI (the first 26 lines of video), which are sent "in the clear". The pulses from the VBI can be used as a reference for a phase-locked loop (PLL) and used to supply the missing pulses for the rest of the video frame. With 20 or so reliable pulses at the beginning of each frame, you can accurately generate the missing 240 or so pulses.
Of the 26 lines in the VBI, lines zero through nine are left alone by request of the FCC, lines 10 to 13 are commonly used to transmit a digital data stream, line 21 contains closed-caption information, while other lines are used for a variety of stuff depending on the cable system and the channel you're watching. When you tune to a scrambled channel with a cable box, logic circuits in the unit count the video lines, read the transmitted data stream, and compare the transmitted data with the information stored in the box.
If the box is authorized to receive the signal with that particular data stream, the decoder is enabled and the scrambled signal becomes viewable. If not, the signal is passed through without being decoded, or more commonly, a barker channel (whose channel number is sent via the data stream) is automatically tuned instead. This prevents people from using the unit as a tuner for add-on descramblers often advertised in the back of electronics magazines.
In the SSAVI system, the video can be sent with either normal or inverted picture information. The descrambler needs a way to determine whether to invert the video or not. Originally this information could be found on line 20, but has since moved around a lot as the popularity and knowledge of the system increased. In any event, the last half of the line would tell the decoder whether to invert the picture or not. If the rest of the field was not inverted, the last half of the line would be black. If the video in the rest of the frame was inverted, the last half of the line would be white.
The Drawing Board column of Radio-Electronics starting in August '92 and going through May '93 described the system and provided several circuits for use on an SSAVI system. Note that audio in the system can be scrambled - usually by burying it on a subcarrier that's related mathematically to the IF component of the signal. Addressable data for Zenith systems is sent in the VBI, lines 10-13, with 26 bits of data per line.
TOCOM SYSTEMS The Tocom system is similar to the Zenith system since it provides three levels of addressable baseband scrambling: partial video inversion, random dynamic sync suppression and random dynamic video inversion. Data necessary to recover the signal is encrypted and sent during lines 17 and 18 of the VBI (along with head-end supplied Teletext data for on-screen display).
The control signal contains 92 bits, and is a 53 ms burst sent just after the color burst. Up to 32 tiers of scrambling can be controlled from the head-end. Audio is not scrambled.
The newer 6000-series converters from Pioneer supposedly offer one of the most secure CATV scrambling technologies from a major CATV equipment supplier. From the very limited information available on the system, it appears that false keys, pseudo-keys and both in-band and out-band signals are used in various combinations for a secure system.
From U.S. patent abstract #5,113,441 which was issued to Pioneer in May '92 (and may or may not be used in the 6000-series converters, but could be), "An audio signal is used on which a key signal containing compression information and information concerning the position of a vertical blanking interval is superimposed on a portion of the audio signal corresponding to a horizontal blanking interval. In addition, a pseudo-key signal is superimposed...so that the vertical blanking interval cannot be detected through the detection of the audio signal…
Descrambling can be performed by detecting the vertical blanking interval based on the information...in the key signal, and decoding the information for the position which is transmitted in the form of out-band data. Compression information can then be extracted from the key signal based on the detected vertical blanking interval, and an expansion signal for expanding the signal in the horizontal and vertical blanking periods can be generated."
Note that Pioneer boxes are booby-trapped and opening the unit will release a spring-mechanism which positively indicates access was gained to the interior (and sends a signal to the head-end on a two-way system, and may disable the box completely.) {See U.S. patent #4,149,158 for details.} The unit cannot be reset without a special device.
Pioneer systems transmit their addressing data on 110.0 MHz, and there are several programmable cubes that can activate these systems. The data is a manchester I encoded FSK signal at ~6kHz data rate.
Some of the early S-A boxes used 6 dB only sync suppression (some of the 8500 models), and some of the 8550 boxes are Tri-mode systems. The three digit number after the model (such as 321) is a code which indicates the make of the descrambler in the unit. Apparently some of the newer S-A boxes use a technique called dropfield, and some of the newer 8600 and 8570 models use baseband methods.
Scientific-Atlanta systems transmit their FSK addressing data on 106.2 or 108.2 MHz. There are several programmable cubes that can activate these systems. On the newest 8600 systems the address data is hidden elsewhere, possibly the video blanking region.
This a secure system which replaces the horizontal sync of each line of video with a three-byte digital word. Video is switched from inverted to non-inverted between scene changes, and the colorburst frequency is shifted up. This is a standard suppressed sync video scrambling method and is relatively simple to defeat with the appropriate circuitry.
However, the three-byte digital word in the area where the sync normally is contains audio and sync information. The first two bytes contain a digitized versions of the audio, the third byte contains sync information and perhaps addressing data. The two bytes of digitized audio are encrypted; a separate carrier signal contains the decryption keys for the digital audio datastream.
Jerrold has gone one step further in scrambling the signal at the baseband level. Other less complicated methods like Tri-mode scramble the signal at the RF level where the channel 73 signal is scrambled when the signal is already modulated on channel 73. With baseband scrambling the signal is scrambled, then modulated on the desired channel. Using this method the scrambling device has more control and more complicated methods can be used.
The most popular way to defeat these systems is to use a test chip or a cube device to activate the original Jerrold equipment. Add-on descramblers are more difficult to build since you have to convert the signal to baseband levels, descramble, then remodulate the signal.
Cable Companies have been experimenting with several new methods of defeating test chips and cubes, most notably is the use of Multi Mode and adding an extra checksum byte in the FSK data packet format. Pirates are starting to clone cable companies test boxes to get around the most problem areas of multi mode and newer test chips and cubes are getting smarter to combat both multimode and the extra checksum bytes.
The research and development division of Fundy Cable Ltd., NCA Microelectronics, has a system dubbed Chameleon. They claim it is a cost-effective solution that prevents pay TV theft by digitally encrypting the video timing information of sync suppression systems.
The company claims the technology has been proven to be effective against pirate and tampered boxes. Supposedly, existing decoders can be upgraded to Chameleon technology with a low-cost add-in circuit, and that the card's sealed custom IC, developed by NCA, is copy-proof.
The VideoCipher system is now owned by General Instrument and is used primarily for satellite signals at this time. VideoCipher II is the "commercial" version which uses slightly watered-down version of the DES (Data Encryption Standard) for encrypted audio.
Video is "scrambled" by deleting the horizontal sync signal. A VC-I descrambler uses line dicing for the video portion and the same audio scrambling scheme as the VCII, but is not available for "home" owners. VideoCipher II is the now-obsolete system which used a relatively simple video encryption method with DES-encrypted audio.
Specifically, the audio is 15 bit PCM, sampled at ~44.1 kHz. It is mu-law companded to 10 bits before transmission. This has recently been replaced by the VideoCipher II+, which has been incorporated as the 'default' encryption method used by VideoCipher IIRS (a smart-card based, upgradeable system).
Coded data relating to the digitized, encrypted audio is sent in the area normally occupied by the horizontal sync pulse in the VCII system. (The Oak Sigma CATV system uses a similar technology.) The Plus format put the datastream data in the HBI.
DigiCipher is an upcoming technology being developed by General Instrument for use in both NTSC and HDTV environments. The DigiCipher format is for use on satellites, and the DigiCable variation will address CATV needs. It provides compression algorithms with forward error correction modulation techniques to allow up to 10 "entertainment quality" NTSC channels in the space normally occupied by one channel.
It provides true video encryption (as opposed to the VCII-series which only DES encrypts the audio). In a Multiple Channel Per Carrier (MCPC) application, the data rate is ~27 MB/second via offset QPSK modulation. Audio is CD-quality through Dolby AC-2 technology, allowing up to four audio channels per video channel.
The system uses renewable security cards (like the VCIIRS), has 256 bits of tier information, copy protection capability to prevent events from being recorded, commercial insertion capability for CATV companies, and more. The multichannel NTSC satellite version of DigiCipher started testing in July of 1992, and went into production several months later.
MAC is an acronym for Mixed Analog Components. It refers to placing TV sound into the horizontal-blanking interval, and then separating the color and luminance portions of the picture signal for periods of 20 to 40 microseconds each. In the process, luminance and chrominance are compressed during transmission and expanded during reception, enlarging their bandwidths considerably.
Transmitted as FM, this system, when used in satellite transmission, provides considerably better TV definition and resolution. Its present parameters are within the existing NTSC format, but is mostly used in Europe at this time.
Two-Piece vs. One-Piece
There are both advantages and disadvantages to the one-piece and two-piece descramblers often advertised in the back of electronics magazines. Most one-piece units are real cable converters, just like you'd get if you rented one from the cable company. It has the advantages of real descrambling circuitry and the ability to fit-in well when neighbors come over (avoids those my box doesn't look like that...or get all these channels! conversations.
A disadvantage is that if you move or the cable company installs new hardware, you may now have a worthless box -- most one-piece units only work on the specific system they were designed for. Another disadvantage is that if the box has not been modified, it can be very easy for the head-end to disable the unit completely.
A two-piece unit (combo) usually consists of an any-brand cable TV tuner with a third-party descrambler (often referred to as a pan) which is designed to work with a specific scrambling technology. The descrambler typically connects to the channel 3 output of the tuner, and has a channel 3 output which connects to your TV. Although some tuners have a decoder loop for such devices.
They have the advantage that if you move or your system is upgraded, you can try to purchase a new descrambler -- which is much cheaper than a whole new set-up. You also can select the cable TV tuner with the features you want , i.e., remote, volume control, parental lockout, baseband video output, etc. Two-piece units typically cannot be disabled by the data stream on your cable.
Note however that there ARE add-on pans manufactured by the same companies who make the one-piece units that DO pay attention to the data stream and can be disabled similarly!
The main disadvantage is that a third-party descrambler MAY not provide as high of quality descrambling as the real thing, and it may arouse suspicion if someone notices your cable thing is different from theirs.
To decode older Jerrold converters, the following chart may be helpful.
__ __ __ __ - __ __ __
| | | | | | |
| | | | | | |____________ T = two-way capability, C = PROM programmable
| | | | | |
| | | | | |____________ DI = Inband decoder, DO = Outband decoder,
| | | | | PC = Single pay channel, A = Addressable
| | | | |
| | | | |______________ Output channel number (3 very common)
| | | |
| | | |________________ D or I = Tri-mode system, N = parental lockout
| | | feature (6 dB-only systems are "blank" here)
| | |
| | |_________________ M = mid-band only, X = thru 400 MHz,
| | Z = thru 450 MHz, BB = baseband
| |
| |___________________ S = Set-top, R = Remote
|____________________ D = Digital tuning, J = Analog tuning
Also note that some Jerrold converters (particularly the DP5 series and some CFTs) have a tamper-switch, and that opening the box will clear the contents of a RAM chip in the converter. This may or may not be corrected by letting the unit get refreshed by the head-end FSK data stream.
Most Jerrold systems in the United States and Canada transmit their addressing data on 97.5, 106.5 or 108.5 MHz. Some DPV7 and DPBB7 models have S7, S8, or S9 as the last numbers on there model numbers, these correlate to 97.5, 106.5 and 108.5 MHz directly.
CFT model numbers almost always use 108.5Mhz. DPV5 and older units mostly use 106.5Mhz. In Europe 122.75 Mhz seems to be the addressing frequency used, at least in several parts of England. The datastream is Manchester II encoded FSK, with approximately a 14kHz clock.
Model 8600 - _ _ _ _
| | | |
| | | |___ Impulse PPV Return: N=none, T=telephone, R=RF
| | |_____ Dual cable option: N=none, D=dual cable
| |_______ Descrambler type: S=SA standard, K=oak
|_________ Channel: S=selectable channel 3/4
The 8600 has 240 character on-screen display, multimode scrambling,
8 event 14 day timer, and is "expandable".
Model 859_ - 7 _ 7 _
| | |
| | |__ Dual cable option: D=dual cable
| |______ Descrambler: 5=SA scrambling+video inversion,
| 7=5+Oak
|____________ 0=No Impulse PPV, 5=Telephone IPPV, 7=RF IPPV
The 8590s feature volume control, multimode scrambling, 8 event
14 day timer...
Model 858_ - _ 3 _ - _
| | | |__ Dual cable option: D=dual cable
| | |______ Data carrier: 6=106.2 MHz, 8=108.2 MHz
| |__________ Channel: 3=channel 3, 4=channel 4
|______________ 0=No Impulse PPV, 5=Telephone IPPV, 7=RF IPPV
The 8580s use dynamic sync suppression, 8 event 14 day timer, and
built-in pre-amp.
The 8570 is similar to the 8580.
Model 8550 - _ _ _
| | |__ 1=108.2 MHz data stream
| |____ Jerrold, dropfield, SA descrambling
|______ Channel: 3=channel 3
The 8550 is not a current model; it can be replaced with an 8580-321.
Non-addressable products include the 8511, 8536, 8540 and 8490.
The SA models below 8600 transmit there FSK addressing data on one of two frequencies.
MARKET CODES Note that almost every addressable decoder in use today has a unique serial number programmed into the unit -- either in a PROM, non-volatile RAM, EAROM, etc. This allows the head-end to send commands specifically to a certain unit to authorize a pay-per-view events, for example.
Part of this serial number is what is commonly called a market code, which can be used to uniquely identify a certain cable company. This prevents an addressable decoder destined for use in Chicago from being used in Houston. In most cases, when a box receives a signal with a different market code, it will enter an error mode and become unusable.
This is just a friendly little note to anyone who might consider purchasing a unit from the back of a magazine -- if the unit has not been modified in any way to prevent such behavior, you could end up with an expensive paper weight.
Test chips are used to place single-piece converters that is, units with both a tuner and a descrambler into full service. There are a number of ways to accomplish this, but in some cases, the serial number/market code for the unit is set to a known universal case or, better yet, the comparison checks to determine which channels to enable/disable are bypassed by replacing an IC in the unit.
Hence, the descrambler will always be active, no matter what. This latter type of chip is superior because it cannot be disabled and is said to be bullet proof, even if the cable company finds out about a universal serial number. When the cable company finds out about a universal serial number, it is easy for them to disable the converter with a variation on the bullet described below.
Another type of test device has been advertised in magazines such as Electronics and Nuts & Volts. It's called a cube and it simulates the addressing data signal test signal for a cable box, most commonly for those from Pioneer and Jerrold. The Zenith data stream is sent in the VBI, making this approach more difficult.
You plug the cable into one side, where it filters out the real data signal, and out the other side comes a normal signal, but with a new data stream. There are also wireless cubes which you just periodically set near your box with the cable disconnected to refresh it.
This new data signal tells whatever boxes the cube addresses to go into full-service mode, including any cable company-provided boxes. Sometimes it is a non-destructive signal, and if the cube is removed from the line, the real data signal gets to the electronics inside and the converter goes back to normal non-test mode.
Note that sometimes it is destructive. There are some cubes that re-program the electronic serial number in a converter to a new value. This type has the advantage that it will work with any converter the cube was designed to test but changes the serial number to some preset value.
The non-destructive versions of a cube usually require that you provide the serial number from the converter you're interested in testing. That way a custom IC can be programmed to address that converter with the necessary data. Otherwise the converter would ignore the information, since the serial number the cube was sending and the one in converter wouldn't match.
First and foremost, the "Bullet" is nothing more than the normal cable FSK data stream with the appropriate code to disable a converter which has not been acknowledged by the cable company. For instance, the head end could send a code to all converters which says unless you've been told otherwise in the last 12 hours, shut down.
All legitimate boxes were individually sent a code to ignore this shut down code, but the pirate decoders didn't get such a code because the cable company doesn't have their serial number. So they shut down when the see the bullet code.
The bullet is not a harmful high-voltage signal or something as the cable companies might like you to believe. If it was, it would damage anyone with a cable-ready TV or VCR connected to the cable and certainly not something the cable company wants to deal with!
The only way to get caught by such a signal is to contact the cable company and tell them your illegal descrambler just quit working for some reason. Not a smart thing to do, but you'd be surprised, especially if it's someone else in the house who calls, like a spouse, child, babysitter, etc. While we're on the subject, it's also not a good idea to have cable service personnel come into your residence and find an unauthorized decoder. Don't hack on cable company decoders.
The cable company can use a technique called Time Domain Reflectometry (TDR) to try and determine how many devices are connected to your cable. In simple terms, a tiny, short test signal is sent into your residence and the time domain reflectometer determines the number of connections by the various echoes returned down the cable. Since each device is at a different point along the cable, they can be counted.
Each splitter, filter, etc. will affect this count. A simple way to avoid being probed is to install an CATV amplifier just inside your premises before any connections. This isolates the other side of the cable from the outside, and a TDR will only show one connection to the amplifier. Radio-Shack sell these as "Splitter Amplifiers" for about $15.00.
The cable company also has various ways of detecting signal leaks in their cable. The FCC requires them to allow only so much signal to be radiated from their cables. You may see a suspicious looking van driving around your neighborhood with odd-looking antennas on the roof. These are connected inside to field strength meters which help locate where the leaks are coming from so they can be fixed thus preventing fines from the FCC!
If you've tampered with a connection at the pole , say to hook up a cable that had been disconnected and didn't do a good job, chances are the connection will "leak" and be easily found by such a device. This can also happen inside your residence if you use cheap splitters/amplifiers or have poorly-shielded connections.
The cable company will ask to come inside, and bring with them a portable field strength meter to help them locate the problem. Often they will totally remove anything causing the leak, and may go further, e.g., legal action, if they feel you're in violation of your contract with them with which you have already agreed to by paying your bill.
Obviously it's a bad idea to let cable service personnel into your house if you are doing something you shouldn't ,but if you don't let them in, as is your right, it will definitely arouse suspicion. Eventually you will have to let them in to fix the "leak", or they will disconnect your cable to stop the leak altogether.
There are many ways for a pirate to get caught. Since stealing cable is illegal in the U.S., you can be fined and sent to jail for theft of service. Cable companies claim to lose millions of dollars in revenue every year because of pirates, so they are serious in their pursuit of ridding them from their system.
A pirate will often show-off the fact they can get every channel to their friends. Pretty soon lots of people know about it, and then the cable company offers a "Turn In A Pirate And Get $50" program. A "friend" needs the money and turns the Pirate in.
A pirate or more likely, unsuspecting housemate of a pirate who knows nothing about what's going on calls the cable company to report a problem with the equipment or signal. The cable company makes a service call and finds gray-market equipment connected to the cable.
During a pay-per-view event such as a fight, the cable company offers a free T-shirt to all viewers. Little does the "Pirates" know that just before that message appeared on the screen, legitimate viewer's boxes were told to switch to another channel while still displaying the original channel number.
So now the legitimate subscriber continues to see the "original" signal, without the T-shirt offer, while the pirate gets an 800 number plastered on the screen. The pirate calls, and the cable company gets a list of all potential pirates...
The cable company temporarily broadcasts some soft-core pornography onto what is supposed to be The Disney Channel (and vice-versa). They simultaneously reprogram subscriber converters to re-map the channels correctly, so the change is transparent to all but non-company converters. Those who call to complain about the "non-Disney" entertainment (or cartoons on the Playboy channel are more than likely to have gray-market decoders.
A big cable descrambler business gets busted. The authorities confiscate their UPS shipping records and now have a list of "customers" who most likely ordered descramblers for illegitimate use. Unconfirmed reports of the cable company driving around with special equipment allowing them to determine what you're watching on your TV have also been mentioned. But this is unlikely.
Of course, the best thing to do is simply pay for what you watch! Then you don't have to worry about the possibility of a prison term, criminal record, hefty fine, etc.
In May of 1990, Radio-Electronics magazine published an article on building a universal descrambler for decoding scrambled TV signals. There has been much talk on the net about the device, and many have found it to be lacking in a number of respects. Several modifications, hoping to fix some of the problems have also been posted, with limited success.
The Universal Descrambler relies on the presence of the colorburst for its reference signal. In a normal line of NTSC video, the colorburst is 8 to 11 cycles of a 3.579545 MHz clock (that comes out to 2.31 microseconds) which follows the 4.71 microseconds of horizontal sync during the horizontal blanking interval.
Since a large number of scrambling systems depend on messing with the horizontal sync pulse to scramble the picture, the Universal Descrambler attempts to use the colorburst signal to help it replace the tainted sync pulse. Unfortunately, random video inversion is still a problem, as are color shifts which occur from distorted or clamped colorburst signals, etc. Most people have not had very good results from the system, even after incorporating some modifications.
CATV: Acronym for Community Antenna television. Originally cable TV came about as a way to avoid having everyone in a community have to spend a lot of money on a fancy antenna just to get good TV reception. Really all you need is one very good antenna and then just feed the output to everyone. It was called Community Antenna Television (CATV). Of course, it has grown quite a bit since then and everyone now just calls it cable TV. The old acronym still sort-of works.
Converter: A device, sometimes issued by the cable company, to "convert" many TV channels to one specific channel, usually channel 3. Used early-on when VHF & UHF channels were on different dials (and before remote controls) to provide "convenience" to cable customers. Now mostly considered a nuisance, thanks to the advent of cable-ready video equipment, they are mainly used as descramblers.
An "addressable" converter is one that has a unique serial number and can be told individually by FSK or other signal, by the head-end to act in a certain manner such as enabling channel x, but not channel y. Addressable converters nearly always contain descramblers for decoding premium services subscribed to by the customer.
Colorburst: Approximately 8 to 10 cycles of a 3.579545 MHz clock sent during the HBI. This signal is used as a reference to determine both hue and saturation of the colors. A separate colorburst signal is sent for each line of video, and are all exactly in phase to prevent color shifts.
Control Signal: The first 11.1 microseconds of a line of NTSC video. The signal area from 0 to 0.3 volts (-40 to 0 IRE units) is reserved for control signals, the rest for picture information. If the signal is at 0.3 volts (or 0 IRE) the picture will be black. See IRE Units; Set-up Level.
Cube: A test device that generates an FSK signal to the cable box to activate itself into full service mode also called FSK device or FSK unit. The first Cubes were named because of the cube shaped box that they were sold in.
Field: One half of a full video frame. The first field contains the odd numbered lines, the second field contains the even numbered lines. Each field takes 1/60th of a second to transmit. Note that both fields contain a complete vertical-blanking interval and they both should have the same information during that interval. Since the NTSC standard is 525 lines, each field contains 262.5 lines--therefore it's the half-line that allows the two fields of a frame to be distinguished from one another. See Frame; Line.
Frame: An NTSC video signal which contains both fields. A frame lasts 1/30th of a second. See Field; Line.
FSK: Acronym for Frequency Shift Keying. A common data modulation method. Addressable cable systems usually send there control information using this method.
FSK Device: See Cube.
Head-end: The main cable distribution facility where your CATV signal originates from. Easily identified by several large satellite dishes, some smaller ones, and usually an antenna tower.
HBI: Acronym for Horizontal Blanking Interval. The first 11.1 microseconds of a line of video. It contains the front porch, the 4.71 microsecond horizontal sync pulse, the 2.31 microseconds of colorburst, and the back porch. The horizontal sync pulse directs the beam back to left side of the screen. Almost every scrambling method in use today mutates this part of the signal in some way to prevent unauthorized viewing. See Colorburst.
Interlace: Term used to describe the dual-field approach used in the NTSC standard. By drawing every other line, screen flicker is increased--but if all the lines were painted sequentially, the top would begin to fade before the screen was completely "painted". Computer monitors, which do "paint" from top to bottom, do not have the problem due to higher refresh rates.
IPPV: Impulse Pay-Per-View. A method whereby a viewer can order a pay-per-view event "on impulse" by just pushing an "Order" (or similar) button on a remote control or cable converter keypad. A customer's purchases are sent back to the head-end via a standard telephone connection (the converter dials into the cable co. computer and uploads the data) or via radio frequency (RF) if the cable supports two-way communication (most don't). A pre-set maximum number of events can be ordered before the box requires the data to be sent to the head-end for billing purposes.
IRE Units: IRE is an acronym for Institute of Radio Engineers. The NTSC standard calls for a peak-to-peak signal voltage of 1 volt. Instead of referring to the video level in volts, IRE units are used instead. The IRE scale divides the 1- volt range into 140 parts, with zero-IRE corresponding to about 0.3V. The full scale goes from -40 IRE to +100 IRE. This is convenient scale to make a distinction between control signals (< 0 IRE) and picture signals (> 0 IRE). See Control Signal.
Line: A video signal is a series of repeated horizontal lines, consisting of control and picture information. The color NTSC standard allows a total time of 63.56 microseconds for each line, and each frame is composed of 525 lines of video information. The first 11.1 microseconds make up the horizontal blanking interval, or control signal, the following 52.46 microseconds make up the picture signal. See HBI; VBI.
NTSC: Acronym for National Television Standards Committee (or Never The Same Color, if you prefer.
Picture Signal: The 52.46 microseconds of signal following the control signal. Information in this area is between 0 and 100 IRE units. See IRE Units.
PPV: Acronym for Pay-Per-View. A revenue-enhancing system where customer's pay to watch a movie or event on a "per view" basis. Customers usually place a phone call to a special number and order the event of their choice; some systems provide Impulse PPV. The presence of a PPV movie channel or your system guarantees you have addressable converters. See IPPV.
Set-up Level: Picture information technically has slightly less than 100 IRE units available. That's because picture information starts at 7.5 IRE units rather than at 0 IRE units. The area from 0 to 7.5 IRE units are reserved for what is commonly called the "set-up level". Having a small buffer area between the control signal information and the picture information is a "fudge factor" to compensate for the fact that real-life things that don't always work as nicely as they do on paper. :-) See IRE Units.
VBI: Acronym for Vertical-Blanking Interval. The first 26 lines of an NTSC video signal. This signal is used to direct the beam back to the upper-left corner of the screen to start the next frame. In order for the horizontal sync to continue operating, the vertical pulse is serrated into small segments which keep the horizontal circuits active. Both actions can then take place simultaneously. The VBI is the most common place for "extra" information to be sent, such as various test signals, and in some cable systems, a data stream.
TELEVISION FREQUENCY CHART The following chart lists frequency information for the "standard" carrier sets. In an HRC (Harmonically Related Carrier) system, all picture carrier frequencies are derived from a 6 MHz oscillator, so all channels except 5 and 6 will be 1.25 MHz lower than usual. Channels 5 and 6 will be 0.75 MHz HIGHER than usual. An IRC (Incrementally Related Carrier) system, all channels are at their normal frequency except for channels 5 and 6, which will be 2 MHz higher than usual.
Some older TV sets can't receive any channels except 5 and 6 on an HRC system, and can't receive channels 5 and 6 on an IRC system. This is also true of some cable converters. A few converters are set up to allow HRC or IRC operation but with channels 5 and 6 on different numbers -- 55 and 56, or 55 and 66.
VHF-Low Band
Center Video Color Sound Osc.
Channel Band Freq. Carrier Carrier Carrier Freq.
TVIF 40-46 43 41.25 44.83 47.75 ---
2 54-60 57 55.25 58.83 59.75 101
3 60-66 63 61.25 64.83 65.75 107
4 66-72 69 67.25 70.83 71.75 113
5 76-82 79 77.25 80.83 81.75 123
6 82-88 85 83.25 86.83 87.75 129
FM (Pseudo)
FM-1 88-94 91 89.25 92.83 93.75 ---
FM-2 94-100 97 95.25 98.83 99.75 ---
FM-3 100-106 103 101.25 104.83 105.75 ---
VHF-Mid Band (CATV)
A2-(00) 108-114 111 109.25 112.83 113.75 155
A1-(01) 114-120 117 115.25 118.83 119.75 161
A-(14) 120-126 123 121.25 124.83 125.75 167
B-(15) 126-132 129 127.25 130.83 131.75 173
C-(16) 132-138 135 133.25 136.83 137.75 179
D-(17) 138-144 141 139.25 142.83 143.75 185
E-(18) 144-150 147 145.25 148.83 149.75 191
F-(19) 150-156 153 151.25 154.83 155.75 197
G-(20) 156-162 159 157.25 160.83 161.75 203
H-(21) 162-168 165 163.25 166.83 167.75 209
I-(22) 168-174 171 169.25 172.83 173.75 215
VHF-High Band
7 174-180 177 175.25 178.83 179.75 221
8 180-186 183 181.25 184.83 185.75 227
9 186-192 189 187.25 190.83 191.75 233
10 192-198 195 193.25 196.83 197.75 239
11 198-204 201 199.25 202.83 203.75 245
12 204-210 207 205.25 208.83 209.75 251
13 210-216 213 211.25 214.83 215.75 257
VHF-Super Band (CATV)
J-(23) 216-222 219 217.25 220.83 221.75 263
K-(24) 222-228 225 223.25 226.83 227.75 269
L-(25) 228-234 231 229.25 232.83 233.75 275
M-(26) 234-240 237 235.25 238.83 239.75 281
N-(27) 240-246 243 241.25 244.83 245.75 287
O-(28) 246-252 249 247.25 250.83 251.75 293
P-(29) 252-258 255 253.25 256.83 257.75 299
Q-(30) 258-264 261 259.25 262.83 263.75 305
R-(31) 264-270 267 265.25 268.83 269.75 311
S-(32) 270-276 273 271.25 274.83 275.75 317
T-(33) 276-282 279 277.25 280.83 281.75 323
U-(34) 282-288 285 283.25 286.83 287.75 329
V-(35) 288-294 291 289.25 292.83 293.75 335
W-(36) 294-300 297 295.25 298.83 299.75 341
VHF-Hyper Band (CATV)
AA-(37) 300-306 303 301.25 304.83 305.75 347
BB-(38) 306-312 309 307.25 310.83 311.75 353
CC-(39) 312-318 315 313.25 316.83 317.75 359
DD-(40) 318-324 321 319.25 322.83 323.75 365
EE-(41) 324-330 327 325.25 328.83 329.75 371
FF-(42) 330-336 333 331.25 334.83 335.75 377
GG-(43) 336-342 339 337.25 340.83 341.75 383
HH-(44) 342-348 345 343.25 346.83 347.75 389
II-(45) 348-354 351 349.25 352.83 353.75 395
JJ-(46) 354-360 357 355.25 358.83 359.75 401
KK-(47) 360-366 363 361.25 364.83 365.75 407
LL-(48) 366-372 369 367.25 370.83 371.75 413
MM-(49) 372-378 375 373.25 376.83 377.75 419
NN-(50) 378-384 381 379.25 382.83 383.75 425
OO-(51) 384-390 387 385.25 388.83 389.75 431
PP-(52) 390-396 393 391.25 394.83 395.75 437
QQ-(53) 396-402 399 397.25 400.83 401.75 443
RR-(54) 402-408 405 403.25 406.83 407.75 449
UHF Broadcast Band (Broadcast)
14 470-476 473 471.25 474.83 475.75 517
15 476-482 479 477.25 480.83 481.75 523
16 482-488 485 483.25 486.83 487.75 529
17 488-494 491 489.25 492.83 493.75 535
18 494-500 497 495.25 498.83 499.75 541
19 500-506 503 501.25 504.83 505.75 547
20 506-512 509 507.25 510.83 511.75 553
21 512-518 515 513.25 516.83 517.75 559
22 518-524 521 519.25 522.83 523.75 565
23 524-530 527 525.25 528.83 529.75 571
24 530-536 533 531.25 534.83 535.75 577
25 536-542 539 537.25 540.83 541.75 583
26 542-548 545 543.25 546.83 547.75 589
27 548-554 551 549.25 552.83 553.75 595
28 554-560 557 555.25 558.83 559.75 601
29 560-566 563 561.25 564.83 565.75 607
30 566-572 569 567.25 570.83 571.75 613
31 572-578 575 573.25 576.83 577.75 619
32 578-584 581 579.25 582.83 583.75 625
33 584-590 587 585.25 588.83 589.75 631
34 590-596 593 591.25 594.83 595.75 637
35 596-602 599 597.25 600.83 601.75 643
36 602-608 605 603.25 606.83 607.75 649
37 608-614 611 609.25 612.83 613.75 655
38 614-620 617 615.25 618.83 619.75 661
39 620-626 623 621.25 624.83 625.75 667
40 626-632 629 627.25 630.83 631.75 673
41 632-638 635 633.25 636.83 637.75 679
42 638-644 641 639.25 642.83 643.75 685
43 644-650 647 645.25 648.83 649.75 691
44 650-656 653 651.25 654.83 655.75 697
45 656-662 659 657.25 660.83 661.75 703
46 662-668 665 663.25 666.83 667.75 709
47 668-674 671 669.25 672.83 673.75 715
48 674-680 677 675.25 678.83 679.75 721
49 680-686 683 681.25 684.83 685.75 727
50 686-692 689 687.25 690.83 691.75 733
51 692-698 695 693.25 696.83 697.75 739
52 698-704 701 699.25 702.83 703.75 745
53 704-710 707 705.25 708.83 709.75 751
54 710-716 713 711.25 714.83 715.75 757
55 716-722 719 717.25 720.83 721.75 763
56 722-728 725 723.25 726.83 727.75 769
57 728-734 731 729.25 732.83 733.75 775
58 734-740 737 735.25 738.83 739.75 781
59 740-746 743 741.25 744.83 745.75 787
60 746-752 749 747.25 750.83 751.75 793
61 752-758 755 753.25 756.83 757.75 799
62 758-764 761 759.25 762.83 763.75 805
63 764-770 767 765.25 768.83 769.75 811
64 770-776 773 771.25 774.83 775.75 817
65 776-782 779 777.25 780.83 781.75 823
66 782-788 785 783.25 786.83 787.75 829
67 788-794 791 789.25 792.83 793.75 835
68 794-800 797 795.25 798.83 799.75 841
69 800-806 803 801.25 804.83 805.75 847
70* 806-812 809 807.25 810.83 811.75 853
71* 812-818 815 813.25 816.83 817.75 859
72* 818-824 821 819.25 822.83 823.75 865
73* 824-830 827 825.25 828.83 829.75 871
74* 830-836 833 831.25 834.83 835.75 877
75* 836-842 839 837.25 840.83 841.75 883
76* 842-848 845 843.25 846.83 847.75 889
77* 848-854 851 849.25 852.83 853.75 895
78* 854-860 857 855.25 858.83 859.75 901
79* 860-866 863 861.25 864.83 865.75 907
80* 866-872 869 867.25 870.83 871.75 913
81* 872-878 875 873.25 876.83 877.75 919
82* 878-884 881 879.25 882.83 883.75 925
83* 884-890 887 885.25 888.83 889.75 931
Channels 70-83 have been allocated to land mobile communication services. Operation, on a secondary basis, of some television translators may continue on these frequencies.
OTHER REFERENCES Video Scrambling and Descrambling for Satellite and Cable TV by Rudolf F. Graf and William Sheets (ISBN 0-672-22499-2) US $20.00. Published in 1987, it is somewhat dated but is useful for understanding what is happening when a video signal is scrambled. Covered topics include SSAVI, gated sync, sine wave, subcarrier recovery, outband, VideoCipher II, B-MAC, etc. 246 pages.
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