23 But What About The Scrambling Systems Used By Broadcasters, How Do TheseWork?
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This article is from the Satellite TV FAQ, by Gary Bourgois flash@lopez.marquette.mi.us with numerous contributions by others.
23 But What About The Scrambling Systems Used By Broadcasters, How Do TheseWork?
There are a number of "other" scrambling systems used for analogue video
information. These systems are used by broadcasters and closed circuit
channels, and not available to the home user. We are often asked how
the scrambling systems work technically, so here is a brief course in
other scrambling systems:
1) BMAC - Used by AFRTS, Horse Racing Channels, KU band Hospitality
premium channels, Private business feeds (IBM, ETC)
Very complex signal. Multiplex Analogue Component. The color info for the
line is sent as part of the line in video form. Because of this, there is no
viewable video. BMAC gives itself away by the "Shark's Teeth" look to it.
The audio is also hidden in the video signal.
2) Leitch - Used by ABC, Global (Canadian) and some sporting events.
The video is a line renumbering scheme.
The top 120 lines of the screen are put at the bottom and vice
versa, then they are renumbered in their respective half screens. Very
distinctive (just look at ABC or GLOBAL to see it) . Also uses phase
inversion every other line for the color information, which is why it looks
black and white. The shuffling is done by a psuedo random algorithm, and
changes from field to field.
The color is lost because the horizontal sync is much narrower and so the
color burst is in the wrong place.
Audio is 4 level encrypted PCM in the area immediately after the narrow
Horizontal Sync pulse. There are also usually analogue audio subcarriers.
3) OAK ORION - Used by CANCOM for the Canadian feeds, also now used by
North American Chinese Television on K2
Is Oak Orion like Oak sine wave used by some cable companies?
OAK sine wave and OAK orion are very different. OAK ORION is more like
VIDEOCIPHER except that included in the OAK is an inversion bit (on one of
the lines in the vertical interval) that tell the descrambler to run normal
or inverted video. The change from normal to inverted is somehow related to
scene changes, possibly by a trigger based on brightness level. SOmetimes it
will stay in one mode for minutes before switching to the other mode
(positive or negative video)
OAK sine wave puts a big sinewave into a POSITIVE image and fools the
Horizontal sync, thus making the picture TEAR. OAK SINEWAVE always has audio
in the clear. OAK ORION has sound in sync just like Videocipher.
4) Videocipher ONE - Used by CBS and Major League Baseball
Generally the audio is in the clear, and it looks like you are looking
through a wavy watery screen. VC-ONE uses variable psuedo random LINE DELAY
meaning that the beginning of each line of video occurs at a different part
of the scan line. If you squint you can almost make out the picture. The
color information is not exactly right, and the images seem darker than
normal also. VC-ONE was the original system proposed for HBO by MACOM back
in the mid 1980's, but was not adopted due to the expense of the total
system. ALL of these scrambling/descrambling systems are much more expensive
than Videocipher-II. And all are fairly secure. BMAC has been cracked by
pirates at least for the HOSPITALITY channels (Premium movies for Hotels),
but we expect that hole will eventually be plugged. The cracked decoders
will not pick up other services, though.
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