Tv Pirating
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discussion of ssavi scrambling: ssavi stands for suppressed sync, audio video
inversion. this method of encoding video transmissions was developed by the
zenith radio corporation, who manufactures the vast majority of legal
unscramblers used today with this method. suffice to say, ssavi is the antichrist of cable pirates. the system involves several less sophisticated methods combined to produce a severely scrambled signal which is very difficult
to decode without the proper hardware. (ie, a real box.) it is illustrated by
the name: suppressed sync: this is the method discussed in part 1 of this
series, only worse. the sync portion of the signal is not transmitted on an
audio subcarrier, but in lines 1-14 of the picture information which are not
seen on the screen. hence, the box must be able to isolate the first 14 lines
of video and extract the information from them. audio: the audio is transmitted
on a subcarrier in a similar fashion as the sync pulses in part 1. if you will
remember, the audio was normal in the suppressed sync method. video inversion:
the video signal is randomly inverted at the scrambling stage, resulting in a
negative picture when the signal is inverted. (yes, like a camera negative.)
the indicator for
whether the upcoming frame of video will be inverted is also sent in the first
14 lines of video, allowing the box to begin inverting the signal before you
see it.
all of these little bits of evilness exist independently of each other. the
signal may have all, none, or any combination of these things. because of
this, the box must be very intelligent. also, because the box is used so
widely, it must have a tuner, allowing your local transmitter to select what
channel they are using by tuning the box before they give it to you. all this
makes for a real fun time when you go to unscramble your signal.
Box theory: the suppressed sync signal is transved from the first few lines
of video mitted normally in the first few lines of video, which, incidentally,
are transmitted normally. the box sees these 14 normal sync pulses, and calibrates itself to reproduce these sync pulses for the rest of the frame of
video. it then inserts these pulses where they are needed in the signal to
produce a normal picture. this recalibration every frame is necessary,
though. sync pulses occur over 500 times every second, and if the clock were
not constantly revamped, it could get out of sync (oh god) with itself. audio:
the audio is transmitted on a subcarrier deviated about 15khz. all the box does
to the audio is retransmit the audio on the proper frequency. video
inversion: the video signal is randomly inverted, but the mode (inverted vs.
normal) can only be switched between frames, not between fields, making the job
of detection and rein- version slightly easier. the box looks at a portion of
line (2, I think) and based on the logic level at a certain point in this line
of video, the box reroutes the signal through an operational amplifiers
inverting input. as a result, a signal received inverted is now correct, and a
frame of video seen as normal is not routed through the inverter, and sent
straight to the rf modulator, which retransmits the corrected signal to the TV
set, usually on channel 3.
physical description of the zenith ssavi decoder: the box is approx. 11″ by 7″,
and about 2.5″ tall, including rubber feet. it has a round vertical travel
pushbutton switch in the rear left top corner, and in a small metal label on
the top center of the box is engraved
zenith ssavi-1
about 1.5″ by .75″. there are 3 female