Preview Subscription Television in the Scrambled Mode

[danieladamko]

our cable company still uses this scrambling system which is very easy to descramble.

the system started in 1998 and soon they will change to digital broadcasting

[bennybytes]

This is awesome! Scrambled TV channels is wonderful art! I love the digital insanity!

[skiggley]

Actually, the audio subcarrier was detected through a phase lock loop (LM723 if my memory serves me correct). The sync suppression and video inversion was random commanded by a bit sent during the vertical blanking interval and were controlled by bilateral switches. I still have my "contraband" copy of the Zenith SSAVI service manual - with schematics, chip cross reference to generic part numbers and all. We Xeroxed many copies of that manual back in the day...

[munichlager]

You mentioned below that the Zenith tuners made GREAT video signal analyzers. Can you point me to documentation on how to use these tuners? I found one site that describes how to use a tv tuner as a spectrum analyzer!

[kargaroc386]

really, the only thing that SSAVI did was remove the horizontal synchronization signal (the left wide band in the HBI), and inverted the video. all you needed to descramble this was run the video through a timebase corrector, and a video inverter. sound was another thing though. it was moved to another subcarrier. you could use a scanner for that.

keep in mind, this is just a THEORY and i have no evidence to back up this claim.

[wieczoris]

In Europe PAL was inverted for scrambling the analogue Breizh TV signal on Hot Bird satellites, late at night.

I think it is a similar method than the one used in your clip, producing something similar than old photography undeveloped films.

[flycar817]

Ah, those were the days.

[Kargaroc286]

didn't preview also use sync suppression along with inversion!!!??? or did the VCR itself give the video new sync signals?

BTW if you invert the video in video software like sony vegas, then you can see the unscrambled video (but not the audio)

[skiggley]

WSMW 27 (this Preview transmission) used Zenith SSAVI (Sync Suppression and Active Video Inversion). I remember my VCR going nuts trying to record this transmission due to the lack of horizontal sync (when it occurred) screwed up the video reference. On some frames, you can pause this video and you can see the 26-bit command transmitted during lines 11-16 after the vertical blanking pulse. Video code, subscriber access code, program tier code and STV market code is sent on this datastream.

[skiggley]

Right now I'm too cheap (actually I'll redo them with a tuner when I get one)...probably why I was too cheap to "subscribe" to Preview - opting to pirate it instead...

[pvx]

If I'm not mistaken, wasn't SSAVI also used for cable TV as well, by Zenith's "Z-TAC" cable tv boxes?

I remember watching cable tv channels way back when on a cable-ready TV without the Z-TAC decoder required by the cable tv company, and it looked exactly like this (weak sync & inverted picture).

[skiggley]

Zenith Z-TAC is the same as SSAVI but with the addition of the VHF cable TV tuner. SSAVI units had a Zenith System 3 Tuner and IF section in them - the same part found in Zenith System 3 color TV sets from the era minus the VHF receiver components installed on the board, had a varactor tuner in with 1 setting in it that was just preset to the UHF channel set up to receive it. A Z-TAC probably had the full System 3 tuner module in it - the same part in the TV...not sure of that though.

[pvx]

I'm thinking you're correct about Z-TAC boxes having a full Sys3 tuner, since the ones I remember using could tune in VHF channels 2-13, as well as cable channels 14 on up to channel 73, IIRC. Plus, the boxes also had the "Redi-Plug" socket on them, which I've seen on System 3 sets as well (I used to have a 1983-vintage Sys3 set with such a while back, it also had the built-in "Space Phone" speakerphone, although I didn't have the factory remote to be able to use it :-( ).

[skiggley]

I still have quite a few of the old SSAVI boxes around. I remember the tuner assembly was part number 9-151-03C...a very popular replacement tuner that TV shops sold (LOTS have gone bad on the System 3s...wink-wink...). I still have a Blonder-Tongue StarCase box (Channel 68) as well as several "home-brew" "68" boxes I made in 1980-1981. The Zenith tuners made GREAT video signal analyzers...lots of detailed signal ports available.

[Kargaroc286]

why don't you get a tv tuner over ebay or others?