Cable filter?

Discussion in 'General Electronics Chat' started by Mathematics!, Apr 5, 2009.

  1. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
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    Ok , does anybody know what the filter is for?
    I would think if you took this off in the green box you would still need the settop box.

    I guess I am not sure what gives you the free channels is it the settop box or the filter?

    I would think the settop box acts like a modem that tunes into the TV stations frequencies as well as encrypt/decrypt channels. And how they know what channels you should have access to is by the settop boxes mac address.

    But I was reading the link at the bottom and sure enough open the green TV box outside to see what was in it. It had 4 coaxial cables with tags on them. The tags had the names of the houses (i.e the addresses for each house)

    I did see a filter on my houses coaxial but I am wondering why they even need it?
    Because You have the settop box why do they need the filter to?

    Here is the link

    http://pulltheskydown.com/ideas/103
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    In my part of Canada filters were used to block "premium channels" on cable TV about 20 years ago. Maybe they are still used today in 3rd world countries. Pay per view channels used to be scrambled.

    Now my cable TV is almost entirely digital and needs a decoder box that is rented and programmed by the cable TV company. I have a big TV with the decoder box and I subscribe to a certain package of stations. I have a little TV that picks up the basic analog stations.
     
  3. wr8y

    Active Member

    Sep 16, 2008
    232
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    Take the filter out and find out - if you have already entered the Cable Company's box illegally, go all the way and see if you can steal some service, too.

    Check back and let us know how you did. There are any number of people interested in stealing any thing they can, probably as many on this site as on any other.

    I left the cable industry in 1980, when the filter took out our ONE premium channel! Hard to say what they are doing now. My cable is the elcheapo analog 50 channel service - no set top box, no digital convertor and no filter at the pole.
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    It could also be simply there to prevent reciprocal mixing and other nasty artifacts of one's tv feeding back into the system. Every receiver has some of these oscillator and mixer products...when added together in a network they can be horrendous.

    Eric
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    Any filters in a cable distribution box are going to be eliminating the video from the internet cable, and the internet frequency from interfering with the tv. The set top box determines what tv channels will get through to your tv.
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The filter inside is a notch filter for a specific frequency.

    That technology isn't used in the US anymore, since Digital TV has become mainstream.

    If the 'premium channels' have color and sync problems (mostly black and white/"ripped" picture), then that filter is what "unlocks" the channel. If the channel has other interference, that filter won't do anything.

    As far as the design and frequency, it depends on your cable carrier, who is probably not going to supply the information. I know that any values I have would be useless in Canada, and illegal in the USA, so I won't give them out.
     
  7. wr8y

    Active Member

    Sep 16, 2008
    232
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    Really? My comcast service has one drop to the house. On the side, there is a four-way splitter.

    One cable goes to the living room TV (no set top convertor, all analog service cause digital tv rots your brain and costs too much)
    One cable goes to the bedroom TV outlet (no TV in there - it interferes with your sex life)
    One cable goes to the phone modem/box/thingy.
    One cable goes to the wireless internet router/box/thingy.

    No filters anywhere, cept in the "front end" of the TV and the 'boxes'.
     
  8. wr8y

    Active Member

    Sep 16, 2008
    232
    1
    But that would not be so much a filter, but a circulator/isolator, right? I mean, the cable TV spectrum is so wide-band, how could you filter out the nasty artifacts of a TV's L.O. without taking out a part of the spectrum carrying program into the house? :confused:
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Fiddling with your cable company's equipment is not a good idea.

    If you go in there and start messing around removing or adding things, you might wind up with a big, nasty bill from your cable company; the difference in what you were paying for vs what you were actually getting, back to when you first started subscription with that company, or the last time they audited the box; whatever is more convenient for them.

    Just don't do it. It's theft of service, and when they eventually catch you (and they very likely will) you'll be forced to pay up; and it'll likely cost you a good deal more than if you had done it the honest way to begin with.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    Many years ago I had a filter installed to prevent me from watching the "premium" channels that I did not want to pay extra for.
    I complained about interference on ordinary channels and the cable repairman removed the filter and the interference was eliminated. Then I could watch premium channels for free whenever I wanted to.
     
  11. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
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    I am not going to modify anything I am just learning how everything connects together and works.

    I want to know what is on the coaxial cable maybe this not a filter.
    Maybe it's to prevent noise don't know look at the pictures to see if you can decipher the plug

    Their is like a red cap or something on them.

    Their is 3 cables in the green box with tags on them that give the address number of which coaxial cable corospondes to which house.

    I am curious why some tags are green while some are blue ...etc etc

    If this is just all for noise then the settop box controls what station's you get now.

    So the settop box gets you the higher channels and descrambles them for you, and convert digital to analog (DAC).

    What is the priemum channels anyway???
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Those shiny silver things with the red/orange rings on them are just coaxial cable connectors that are sealed against moisture. They are much better than the older style crimp-on coaxial connectors, which would corrode after a couple of years. They are not filters.

    Frequently, the color of the tags doesn't mean anything; they're just there to label which apartment or house address that coaxial cable is wired to.

    It used to mean what type of service (or no service) that the address was supposed to get, but nowadays they have it computerized, so the color doesn't really matter.

    "premium channels" are like HBO, Showtime, etc. You pay extra for access to them.
    There are also "pay per view" channels, but you need to have a digital box to access them.
     
  13. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
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    Ok I have a few last questions.
    premium channels how do they restrict access to these ?
    Is it the set-top box (i.e cable box) that works like a cable modem which authentic's you by mac address or something like that. Then they have some kind of server communicating back to the box telling it what station it can tune into / decrypt ?

    Or does the cable provider physically have to plug your wire into a different broadcasting wire?

    And I am curious to know why plugging the coaxial into a TV directly with no cable box. You can only access a few channels. Is this because the standard TV tuner circuit in the TV can't tune into some higher stations.

    Or is it because you need the cable box to allow you to descramble and tune into higher stations?

    Because I believe that cable is a shared network so the stations should all be their on everybodies wire. So it must be because you need a specific tuner that a standard TV doesn't have to tune into some stations.
    Or it must be for it to decrypt your stations based on the mac address of the set-top box.
    Or both.

    Anybody know for sure.
     
  14. Audioguru

    New Member

    Dec 20, 2007
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    My analog cable TV stations go up to cable channel 65. My TV can tune up to cable channel 120.
    My digital cable TV stations go up to nine hundred and something but I don't pay for most of them so I am denied access to the ones I don't pay for. My cable TV box converts the digital stations that I pay for to analog for my TV.
     
  15. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
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    How do you know what TV stations are broadcast as analog and which are digital?

    Assuming your right
    Then are all the analog channels free.
    That is are they broadcasted with no encryption or no need to descramble?

    How do you know which stations are free is their some kind of standard for what stations must be broadcasted free?

    And when the cable box converts the digital stations to analog doesn't it have to map the analog station onto one of the 65 or 120 channels so the TV can process the stations?

    Either way I had an old cable box and I cann't just plug it in and use it.
    I had to call the cable provider each time I got a new cable box to first activate it.
    And I think they ask for the serial or mac address before I could get the channels. I don't see why since I thought cable is a shared network. It's all going down the coaxial cable to everyones house so if you have a tuner that tunes into that frequency it should beable to get that station.
     
    Last edited: Apr 6, 2009
  16. SgtWookie

    Expert

    Jul 17, 2007
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    Yes.

    No. Cable systems are broadband, from low freqency up to nearly 2GHz.

    The digital channels use different frequencies and a different format than your standard TV tuner. The set-top box reconstructs the digital signal into something your TV can produce sound/picture from.

    Most cable companies place a number of analog stations on the cable that you can see with just a standard TV tuner. There may even be a couple of "teaser" premium channels thrown in the mix.

    It takes the set-top box to convert the company's proprietary digital signals to something your TV can understand. And yes, the "box" has a MAC address, and the channels that you have paid for are programmed into the box.

    If you don't pay your cable bill, they can turn all of the channels off, and even put a message on your screen to call your cable company's billing office, or something similar.
     
  17. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    It is horribly complicated in an all analog system, and pretty easy with digital cable.

    A signal does not have to be digital to be encrypted.

    Rough analogy: You write a message to send to several people, but you want it encrypted. You add the public key of everybody you want to read the message during encryption. Lots of people can see it, but only those with the correct key can read it.

    Cable boxes have encrypt/decrypt hardware as well as "keys", some have transmit abilities. Some cable networks now know exactly who is watching what channel, if they switch when a commerical is on, etc...

    The available bandwidth on a coax line is massive, compared to twisted pair or "over the air". They use quite a bit of it for services such as Internet, Phone (VoIP and analog), pay per view back channels which are all encrypted, etc. Back when notch filters were used to block pay channels, "the box" was simply a broadband amplifier to keep signal levels up. Present day, the box outside doesn't simply tie all the wires together to an amp, it functions more like an Ethernet switch, keeping traffic "local" to a subscriber and the cable company.
     
  18. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
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    So in theory if you changed the cable boxes mac address to your next door neighbor (if you knew it) then you would get the exact channels he is getting?

    And if you didn't pay your bill's they can send some type of packet down to the cable box telling it not to unlock the cable stations.
    So then their must be some type of protocal followed.

    I have read that for internet they encrypt all upstream and downstream packets. This is because cable is a shared network and anybody with wireshark could sniff for packets. But if they where encrypted then they would still have to decrypt them which is almost impossible.
    My main question is how much of the channels counting internet and VOIP ...etc down the coaxial cable are encrypted. I know some stations like the first 62 or so are public stations and must be broadcasted free for everybody to view no matter what (this is some kind of FCC regulation every cable provider must broadcast those channels free of charge)

    As for the day of the filters to get free HBO ,,...etc all the cable guy would have to do is take off the filter? So is that why the saying if you slip the cable guy a few extra dollars he will give you the free premium channels. (moive cable guy :)

    Anyway what was the descrambler for was this only to decrypt analog stations. I don't here much about descramblers any more I forget what their purpose was. I don't really think descramblers will work now that they do it thru the mac address of the cable box
     
    Last edited: Apr 6, 2009
  19. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    It isn't just the MAC address (hardware address) of the box. It is high grade key encryption, many boxes need to have the final manufacture or firmware flash done inside the US for that reason (encryption import/export laws). Often, it is when shipping to specific cable vendors.

    Encryption hardware has been in cable boxes since the 80's. Not 32 bit DES, or ROT13 + XOR, but advanced ciphers. Currently Elliptical Curve and other "base" encryption is in Cable Boxes, DVD Players, and built into the BIOS of every computer motherboard stamped "Vista Ready". Regarding how deep the rabbit hole goes, check out the deep background on "Clipper Chip" (big news 15 years ago).

    The encrypt/decrypt is implemented in ASIC and runs "at data link rate". The keys are long and unique. Data is processed by the same "decoding/demultiplexing" unit, so a non encrypted compressed stream essentially goes through the same steps as an encrypted compressed stream. Each item with a MAC has multiple keys, all proprietary to vendor that match the head units and distribution points, but only one per MAC is used at a time, often the life of the box.

    If a compromised key is detected, the key is immediately blacklisted. Similar revocation goes for computer BIOS keys, Windows licenses, and the underlying majik for decoding Blu-Ray and other "unbreakable" content protection. The big money companies have it set up so a user needs to go to big lengths to identify himeself as "proper owner" in order to be 'activated' again (use another key). In that event, that person made "The List". All the laws passed about steep fines for "copying" have been "unenforceable". They are closing that gap extremely quick.

    There are procedures in place for contingencies such as a disgruntled geek working at the fab shop anonymously dumping a keylist. Those keys are simply flagged compromised, and equipment will function long enough to be re-activated, worse case being a flash of EEPROM over the network. BTW, did you notice how you can browse the web from BIOS on new systems? It's all for user convenience! Really!

    Cable boxes and DVR systems from cable companies follow similar "scorched earth" policies with their encryption. Hollywood/Macrovision does not want to let security through obscurity "bite" them again, like everything else they've tried (CSS on DVD, many revisions of 'Macrovision' on video tapes, etc).

    Vista and Windows 7 Hardware and drivers must be 100% encrypted on the wire. If a device allows any potentially copyrighted content to cross a bus in cleartext rather than ciphertext, the hardware or driver is blacklisted. This is the reason so many common video cards, sound cards, USB Ports, and DVD Drives have endless "Driver Issues" when 'upgrading' to Vista. Microsoft made an official statement to the effect of "These restrictions were the only way for clients to use Blu-Ray technology". I honestly don't think they tried hard for any other system. They want all the customer info they can get.

    I know I've focused quite a bit on computers, because it is the easiest parallel. Cable companies #1 concern is piracy of services. Software companies have that ranked lower, because at least pirated software means their product is getting used, and possibly more legit copies will be sold. Not so with Hollywood though.

    Anyway, Cable companies have been trying and changing the technology and all weakpoints for over 30 years. Along with cell phones, cable companies/enterntainment resellers are a huge part of the reason realtime cryptography on a chip is a reality.

    As far as the filters on the wires, They usually need a special wrench to get to for install and removal. If it is an additional "Male/Female Connector" with a color code on it, with no visible nut, that's what you are looking at. How they work is quite ingenious in simplicity. Compared to the methods mentioned above. Different colors for different premium channels (frequencies). The trick is getting the center frequency, attenuation, and Q Exactly right if any of those are off, they not only do not "work", but screw up reception of other channels as well. That last sentence might set off a lightbulb. Remember, it's illegal!

    Sorry about the novel! As much as we'd love to think as the cable companies and software companies as "Greedy Morons", they are anything but stupid. If they seem to be dumb, it's a trap. ;)
     
  20. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
    4
    Yes, I know all about how they do cryptography ...eliptical curves over finite fields ... etc.

    I have my degrees in pure math and computer science.
    But now I am getting into to electronics and programming chips.
    And I was wondering how the cable companies blocked/gave access to their channels.

    I have a friend that was a lines man and he did stuff with the phone (POTS) and cable company so I know how most of the lines go and what they can restrict at a box.

    But I think you nailed it. And it was what I was thinking.
    It is the firmware of the cable box. But I bet if I tried to read the firmware they have some type of bit locking mechanism that would erase the chip.
    So the only way to get free cable is you need to get the source code to the firmware along with some key's and program the chip then solder it in.

    The source code must depend on the mac address with the cable providers key's in some way not sure if they are still using DES or AES. But the only way to know how to get on for free is to have the source code.

    To get the software would be impossible if you didn't have an inside guy.
    And you said they have procedures to make sure the inside guy's don't leek it.
    So almost impossible.
    And even if you did what did you really gain in the long run?

    Hell you could just use bittorrent and download from piratebay or something and save the hasel.
    When you wanted to see a moive.

    Thanks for all your replies
    Cool to know the whole rabbit hole :)
    Thanks again
     
    Last edited: Apr 7, 2009
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