coorswol@alchemy.tcnet.ithaca.ny.us (Curt Coulter) (03/28/91)
I have seen several mentions of this. Where does one get plans for this from? Thanks, -Curt coorswol@alchemy.tcnet.ithaca.ny.us
ramos@cbnewsj.att.com (richard.ramos) (03/30/91)
In article <Ze5HZ3w162w@alchemy.tcnet.ithaca.ny.us>, coorswol@alchemy.tcnet.ithaca.ny.us (Curt Coulter) writes: > I have seen several mentions of this. > Where does one get plans for this from? > Thanks, > -Curt > coorswol@alchemy.tcnet.ithaca.ny.us I'd like to take this question several steps further. What do these things descramble? Do they descramble cable TV signals, satellite signals, some other signals that I don't know about, or all of the above? I've heard that cable companies offer boxes that are addressable from their networks. Are these descramblers detectable by cable companies. What kind of equipment do you need (other that a TV) to receive these signals. I was under the impression that different transmission formats were used by different companies requiring different types of receivers in front of the TV to decode the signals. Morever, I have a hard time believing that there are so few encoding (scrambling) schemes being used that a single box can desramble them all. If you're getting the impression that I know nothing about TV transmission you're right. I'd appreciate any information as to available literature on this subject as well as hearing about people's experiences in building these boxes. Rich Ramos 908-957-6267
tell@oscar.cs.unc.edu (Stephen Tell) (04/02/91)
In article <1991Mar29.235910.21230@cbnewsj.att.com> ramos@cbnewsj.att.com (richard.ramos) writes: >In article <Ze5HZ3w162w@alchemy.tcnet.ithaca.ny.us>, coorswol@alchemy.tcnet.ithaca.ny.us (Curt Coulter) writes: >> I have seen several mentions of this. >> Where does one get plans for this from? It was in an issue of _Radio Electronics_, somtime in the past year. >I'd like to take this question several steps further. What do these things >descramble? Do they descramble cable TV signals, satellite signals, >some other signals that I don't know about, or all of the above? It works on any baseband video signal that has been scrambled with a simple sync-suppression system. Many of the simpler scrambling schemes remove or distort the sync pulses that tell your TV when to begin another horizontal scan line or vertical field. This family of systems use various means to send a "hidden" sync signal elsewhere in the video signal for a legit descrambler to use in reconstructing a good signal. The RE project can handle all of this one family of scrambling systems by ignoring any hidden sync and regenerating its own sync signals. It required you to tell it where the sync signals are by pressing two buttons until the picture drifts the correct horizontal and vertical position. It then stays locked on through use of the color subcarrier. In a correct video signal, there are a exactly the same number of cycles of the 3.579545 MHz color subcarrier in every frame, so by phase locking a sync generator to that a good enough approximation to the original sync can be recreated. It cannot descramble any of the more sophisticated systems, for example the Videocipher system used for most satelite transmissions. (Videocipher uses the DES algorithm to encrypt the digital audio, making it immune to any simpleminded descrambling.) >What kind of equipment do you need (other that a TV) to receive these >signals. You'll need a way to insert the device into the baseband video path; it does not work on RF signals. This usually means a seperate TV tuner and monitor. A VCR can work as the tuner. >If you're getting the impression that I know nothing about TV transmission >you're right. I'd appreciate any information as to available literature >on this subject as well as hearing about people's experiences in building >these boxes. In other issues of Radio Electronics over the years there have been "For information only" articles describing a variety of methods. >Rich Ramos >908-957-6267 -------------------------------------------------------------------- Steve Tell tell@cs.unc.edu H: +1 919 968 1792 #5L Estes Park apts CS Grad Student, UNC Chapel Hill. W: +1 919 962 1845 Carrboro NC 27510