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Cable signal too high?

Discussion in 'General Electronics Chat' started by Dr_Doggy, Nov 11, 2017.

  1. Dr_Doggy

    Dr_Doggy Well-Known Member

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    as a cable tech I have been trained to keep the signal strength within a spec of +/- 10db/mv. obviously there are negative effects when the strength approaches and crosses the -10 range.
    As i have been told and experienced that when the signal gets too high, nearing +10 a distortion occurs and causes data packets to be dropped and can also cause a modem to unlock and reboot or even go offline not being able to detect the RX stream.

    But a debate has broken out with our field reps and maintenance division where maintenance says that a too high signal will cause service issues but will not cause long term damage on the modem unless it is closer to the +20 side of things. however in the field i have seen modems exposed to high signals around +12 suffer from permanent failure but maintenance division says it just isn't so.

    So are the failures im witnessing just coincidence and not really related to the exposure to the +12db signal, or is it possible that im not crazy!!??
     
  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    It has been years, I designed TVs and cable boxes. (old school)
    My boxes were tested to 2000 volts static discharge and 5 to 12 volts of signal. The sets will not work with a 12 volt signal but there was no damage.
    I do not know how your equipment is designed.
    Training may not be correct!
    The repair department knows what needs fixing. They may not know what killed the box.
    If you see failure and those boxes have a high signal that probably means something.

    It is hard to know what really happens.
    The sales department is usually wrong.
    The repair department is often right.
    The field men should be listened to.

    This is from the point of view of R&D.
     
  3. JimB

    JimB Super Moderator Most Helpful Member

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    In my experience, that is true in many areas.

    JimB
     
  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I've no idea specifically about digital cable systems, BUT if a slightly too high signal level can damage the modems then there's something seriously wrong about their design.

    As ronsimpson says, anything even reasonably well designed shouldn't be damaged by volts of signal.
     

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