bender@oobleck.Eng.Sun.COM (memory fault - core dumped) (05/23/91)
Sometimes, I'm amazed at the lack of a sense of humor on some of the newsgroups on the net. For example, below are some excerpts from two articles that I posted to rec.video concerning cable company "spikes" to disable (illegal) descrambler boxes. I posted them in direct response to the fairly large amount of postings concerning descramblers that don't work any more. Now, perhaps I'm mistaken, but I don't see how anyone with an even rudimentary knowledge of video and electronics could have taken my postings seriously, but it seems that many people did, since I've received countless e-mails ranging from "You're an idiot" to fairly detailed dissertations about how the horizontal retrace interval can't POSSIBLY be synchronized to the zero-crossing of the AC line, as well as some "learned" opinions that cable TV distribution amplifiers (those mounted outside on the poles or buried underground) wouldn't be able to pass 50,000 (or 20,000!) volts!! I figured that the "four 5Kv neon sign transformers wired in series" part of my second posting would have given this away as a farce, but apparently not. Maybe I should have included some :-)'s??? >That's not what I heard! I heard (from a FOAF no less!) that the cable >company does indeed send a "spike", but it's during the horizontal retrace >time, so that normal TV's and VCR's won't be affected. The spike is around >50,000 volts with a duration of 20 mS, and is repeated eight times during >the prime-time viewing hours from 8PM until 11PM EST (so that west coast >viewers will of course receive the spike between 5PM and 8PM). Because of >the necessarily high voltage of the spike, it leaks over into some of the >unused cable channels; if you have a Toki Industries CDV-4000 addressable >decoder, you can tune it to channel 85 or greater, and observe the spike >intermixed with the "snow"; the reason that you can see the spike on an >unused cable channel is because unused channels have supressed sync pulses, >and so the AGC in your receiver will be operating at maximum gain, and so >will be able to pick up the 4th and 5th harmonics of the spike that is >transmitted on the lower-frequency cable channels. What the spike does is to >fuse several of the memory locations in a cable converter boxes' ROM (the >chip that provides the instructions as to which channels to receive and >block); by fusing these locations they appear as hex 0x0FF to the converter >descrambling circuitry, which is an invalid channel combination, and so the >converter box goes into an endless self-diagnostic mode, in which none of >the scrambled channels can be descrambled. <You are correct, it's not 50,000 volts at 20mS, it's actually 20,000 volts <at 50mS. Sorry that I got the two numbers confused. But you see, since the <spike is sent out during the horizontal retrace interval, it won't affect <TV's or VCR's connected to the cable, since the start of the horizontal <retrace occurs right at the zero-crossing of line voltage, which is the time <when the equipment connected to the cable uses the filter capacitors on the <DC power supply to supply the power to the internal electronics. <The cable company actually only sends a coded digital pulse (using PWM <techniques) to the cable amps located on the poles or underground, and the <spike is actually generated and sent out from the cable amps. They use a <battery of 4 5Kv neon-sign transformers connected in series that have their <primary windings pulsed at 50mS during the horizontal retrace interval. -- Won't look like rain, Won't look like snow, | DOD #000007 Won't look like fog, That's all we know! | AMA #511250 We just can't tell you anymore, We've never made oobleck before! | MSC #298726
amichiel@rodan.acs.syr.edu (Allen J Michielsen) (05/24/91)
In article <13867@exodus.Eng.Sun.COM> bender@oobleck.Eng.Sun.COM (memory fault - core dumped) writes: >Sometimes, I'm amazed at the lack of a sense of humor on some of the >newsgroups on the net. I posted ... cable company "spikes" to >disable (illegal) descrambler boxes. ,... The really sad or confusing thing is that something sorta similiar is what some cable companies are doing. Many of the new boxes are addressable, meaning that the main office can communicate with the over the cable wire. Illegal boxes can be defined as boxes which, the serial number responds from the wrong zone/location or boxes which respond from several zones/locations, or boxes which respond telling the office it is descrambling servies that don't match the office billing records, or boxes which the office doesn't have serial numbers on file for, or similiar things.... These illegal boxes can be told, by the office computer to shutdown or 'break'. But no 'high-voltage' is involved untill you come into the office with the broken box to get it repaired. This brings to mind a story, some people I knew, paid a local field cable guy (with limited morals...) to do a illegal hookup. The cable company had several services, hbo, sho, cim all available without ANY box, using 'jumpers' at the street. From time to time, during rain storms or whatever, the cable went out or got really fuzzy. Of course the tennants knew enough not to call and complain, but to wait for the problem to go away, get called in by a neighbor, or find this original install person. However, for the summer, they sublet the appartment to some goofy guys w/o this worldy experience. One friday night, during a hobo boxing match, out went the cable. Right on the phone went these drunk guys, with mouths like sailors and.... Quite a bit of trouble was had, and the original tennants ended up paying a ton of money for back cable services..... Now they are actually throwing people in jail for theft of services, etc. I'm not sure how much a year of my life is worth, but legal cable at X$ per month sounds cheaper than Y$ for a illegal box + the % chance of getting caught * a year of my life..... al -- Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University InterNet: amichiel@rodan.acs.syr.edu amichiel@sunrise.acs.syr.edu Bitnet: AMICHIEL@SUNRISE
gil@jts.com (Gil Hauer ) (05/27/91)
In article <1991May23.190150.3982@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: > The really sad or confusing thing is that something sorta similiar is >what some cable companies are doing. Many of the new boxes are addressable, >meaning that the main office can communicate with the over the cable wire. >Illegal boxes can be defined as boxes which, the serial number responds from >the wrong zone/location or boxes which respond from several zones/locations, >or boxes which respond telling the office it is descrambling servies that don't >match the office billing records, or boxes which the office doesn't have >serial numbers on file for, or similiar things.... These illegal boxes can >be told, by the office computer to shutdown or 'break'. But no 'high-voltage' >is involved untill you come into the office with the broken box to get it >repaired. It was my impression that cable television service is basically a one way communication channel (i.e. out from the head-end). Is this not the case any more? If it is one way, how can the descramblers be "polled"? >Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University > InterNet: amichiel@rodan.acs.syr.edu amichiel@sunrise.acs.syr.edu > Bitnet: AMICHIEL@SUNRISE Gil -- -- Gil Hauer gil@jtsv16.jts.com Tech Noir Inc. { torsqnt | suncan | geac | uunet }!jtsv16!gil Toronto, Ontario, CANADA +1 416 653 8276
acm@Sun.COM (Andrew MacRae) (05/28/91)
In article <1991May27.150924.3482@jts.com>, gil@jts.com (Gil Hauer ) writes: > It was my impression that cable television service is basically a one > way communication channel (i.e. out from the head-end). Is this not > the case any more? If it is one way, how can the descramblers be > "polled"? The repeating amplifiers used in cable systems are all two way. At least that is what I was told back in '73 when we used to broadcast our own shows over the community access channel at college. I've always thought that cable would make a nice way for underground groups to communicate.
juraschek@gmuvax.gmu.edu (05/29/91)
In article <4207@jethro.Corp.Sun.COM>, acm@Sun.COM (Andrew MacRae) writes: > In article <1991May27.150924.3482@jts.com>, gil@jts.com (Gil Hauer ) writes: > > It was my impression that cable television service is basically a one > > way communication channel (i.e. out from the head-end). Is this not > > the case any more? If it is one way, how can the descramblers be > > "polled"? > > > The repeating amplifiers used in cable systems are all two way. At least > that is what I was told back in '73 when we used to broadcast our own shows > over the community access channel at college. > > I've always thought that cable would make a nice way for underground groups > to communicate. In the Northern Virginia area, the cable system (Media General - Magnavox boxes, I think) definitely uses a two way system. In fact, the converters are essentially "modems". Each one has a unique address (id) pinned into it. The nice side effect of this is that you can go anywhere in the network with your convertor box, and your customer profile follows you - since it's keyed to the box id. The bad thing is that occasionally some neanderthal in the home office will key in the wrong address (id) when changing a profile, and after power failures, it occasionally necessary to call the guys in the home office to have them deliberately poll your unit so that it handshakes with the home computer to refresh itself. (That is, after a power failure, you sometimes end up with no options, so you have to be "reset". This implies a kind of handshaking.) I've been told that future plans for this system include allowing response polling (The cable guys ask you a question and you punch a button in reply) and the system already will support this. That definitely implies two way communication. -Dave
smasters@gmuvax2.gmu.edu (Shawn Masters) (05/30/91)
Having a fair size broadband cable system here under our department, I'm familiar with the amps that your talking about that are two ways. They all have modules that can be pulled out for either direction. This allows for smaller power consumption(so you have to insert fewer power inserters), MUCH easier balancing, and more channels. Remember to have data going two ways, you have to have two different frequencies. One to amplify in one direction the other to amplify in the other. Sytek(now Hughes Lan Systems), had once told my department that they had help run Media General(fairfax county cable) two ways in small areas for test or communication purposes to sell to the local companies. The extent of this we never found out, but I know the amps they use by my house are ONE-WAY. Shawn C. Masters smasters@cns01.gmu.edu