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cable noise

Discussion in 'TiVo Coffee House - TiVo Discussion' started by cannonz, Nov 1, 2012.

  1. steve614

    steve614 what ru lookin at?

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    May 1, 2006
    Dallas, TX
    Uh-oh, SNJpage1 fell into the same mistake a lot of people make. ;)


    (Hint: not about the subject matter) :p


    Edit: To be fair, I made the same mistake...once. :D
     
  2. cannonz

    cannonz Active Member

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    Oct 22, 2011
    Many years ago came home from work one day had note on door saying I had bad TV or other piece of equipment that was defective causing problem, one of my TV's was disconnected one of those lock things on that tap of splitter. Called,tech came out checked everything said nothing was wrong did not know why someone said it was, hooked TV back up.
     
  3. lrhorer

    lrhorer New Member

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    Aug 31, 2003
    San...
    That is lrhorer, if you please, not irhorer.

    First of all, do you realize that you are speaking to an engineer who worked for a CATV company for 14 years?

    A compromised shield, including one which is compromised by a bad, loose, or improperly crimped connector can most certainly allow external signals to ingress into the coaxial cable. If the ingress signal is at precisely the same frequency (most CATV systems offset their analog signals 100KHz from the OTA carrier) and precisely the same content as the OTA signal, it can produce ghosting. If the content is different, then it produces a different sort of ghost, where one image is superimposed on the other. If the frequencies are offset, it ordinarily produces what is known as the "Venetian Blind" effect, producing wide, alternately bright and dark semitransparent bars over the picture. That may be what you are describing. It is not noise, it is not produced by the connector itself, per se, and it cannot be picked up by an external aerial or coaxial cable. It will not insert itself (to any significant degree) into the feeder or any adjacent tap ports.

    Non-video ingress cariers often produce beats of a different sort. A herringbone pattern or fine horizontal lines are common.

    No one said anything about illegal amplifiers. Indeed, linear amplifiers are quite legal in some bands and below some specified power output.

    At 27 MHz? Not on your life.

    A while back? They have been required by the FCC to do so continuously for decades. They are required to document the cumulative system leakage by flying over every franchise with a special receiver once a year and to provide logs of continuous street-level monitoring and repair or disconnection of drops which produce egress levels above specs. This has nothing to do with noise and is only indirectly related to interference on the CATV drop. As I mentioned, if signals are getting into the drop from OTA sources, then signals are also getting out.

    If it could not be resolved outside, yes. The CATV company for which I worked had a small team (12 people) whose responsibility was pinpointing RF egress. If the problem were related to bad fittings, drops, or passive devices owned by the company, they would fix them. Many were due to illegal hookups, which were often done improperly. These were simply disconnected. The others were forwarded as trouble tickets to the regular technicians.

    I assume no such thing. The visual effects of RF ingress on analog signals are distinct and easily identified. The effects on digital signals are not visually distinguishable from noise, distrotion, or low signal levels, and since digital channels do not have any direct correlation to specific frequencies, it can be very difficult to know the source merely by looking at the TV. It is also much more difficult to describe the effects and their causes to civilians. In addition, the signals levels for analog signals are quite standard throughout the industry. The levels for digital signals are not. Various companies will run their digital carriers anything from 5 dB to 20 dB lower than analog carriers. Most choose either 10 or 15 dB, meaning the inputs to trunk amplifiers are either 0 or -5 dBmV.
     
  4. lrhorer

    lrhorer New Member

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    Aug 31, 2003
    San...
    I have three guesses:
    1. They identified the wrong drop.
    2. There is an intermittent leak. Temperature, wind, and even sometimes humidity can cause leakage levels to vary.
    3. The problem was a loose connector at the pole, or a bad channel trap. Disconnecting the drop and removing any channel traps eliminated the problem. Hooking you back up returned the system to normal operation.
     
  5. lrhorer

    lrhorer New Member

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    Aug 31, 2003
    San...
    'Sounds like your CATV provider did not offset their channels. Most do.
     
  6. lrhorer

    lrhorer New Member

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    Aug 31, 2003
    San...
    I try not to be put off by it, and admittedly it is an easy mistake to make. Lowercase l and uppercase I are quite distinct with ISO-8859-1, however.
     
  7. SNJpage1

    SNJpage1 Active Member

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    May 25, 2006
    Atlantic...
    Once again Irhorer I disagree with you about the CB radio thing. Back when I had one there were a lot of people causing interference on our TV's. We even had to call the FCC about the one guy. The local cable companies wouldnt do anything about them.
    I am not going to get into a pissing contest over who is right or wrong but my personal experience will match your 14 years as an engineer.
     
  8. unitron

    unitron Active Member

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    Apr 28, 2006
    semi-coastal NC
    The difference is visible in your comment, but not in your user name to the left.

    Different fonts, I guess.
     
  9. lrhorer

    lrhorer New Member

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    Aug 31, 2003
    San...
    I asked you once to use my proper handle. I do not think it is an unreasonable request.

    I never said a CB transmission could not cause problems on a TV. You said a CB could cause problems with the cable, and this is simply untrue. If the TV has a poorly shielded IF or Audio section, or possibly even a poorly shielded video section, a 27 MHz signal of sufficient strength could possibly cause an issue. I have seen it myself a number of times, and not just at 11 meters. The issue, however, is *NOT* with the cable or any signals on the cable. It is beyond the RF section of the TV, which will not pass signals below 55.25 MHz, or at least not one of any plausible intensity.

    Nor should they have done. It was not an issue relating to their signals, nor even one on their CATV drop. It was entirely an issue of your TV's shielding and perhaps IF mixer issues and possibly of the CB owner, if he was doing anything illegal in terms of transmitted power.

    Your experience is not at question. It is your conclusions, which are based upon a lack of understanding of the technology involved.
     
  10. unitron

    unitron Active Member

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    Apr 28, 2006
    semi-coastal NC
    Actual hams, that is, those with FCC licenses and assigned call signs to operate on the amateur bands, are unlikely to be running illegal equipment. Part of the "thrill" for them is to get maximum performance within the legal restraints.

    There are, of course, others who operate outside the law and give them a bad name because the public doesn't know the difference.
     

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