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Signal Intensity Vs Signal Quality

  • 17-01-2009 4:46pm
    #1
    gtg60
    Registered Users, Registered Users 2 Posts: 1,759 ✭✭✭


    This seems to be a bit of a mystery to me, on my STB (a Sigmatek DVB-500), I can often get 100% Signal intensity but Signal quality never rises above 70~72%, picture always looks great but can anybody explain this to me a little better? And is there a direct correlation between both? And if I could get the Signal quality up, would the picture improve?


Comments

  • #2
    watty
    Registered Users, Registered Users 2 Posts: 32,445 ✭✭✭✭watty


    The TV signal has FEC (Forward Error Correction). Once the errors are below a certain level (often greater than 50% quality), the picture is as good as it can be as the errors are corrected.

    More quality above 55% or 60% is unlikely to give any better picture even at 100%.

    The signal LEVEL is hardly relevent at all as long as it is not too low or too high.

    If the Intensity/Strength is over 80%, sometimes the signal quality will improve with a 6dB attenuator on the tuner input, but unless the quality is below 45% you would not see any difference.

    Satellite TV often uses FEC 3/4 or 5/6, but feeds not meant for home may be 7/8, requiring a very large dish as the FEC is lower and thus less errors can be corrected.

    An amplifier on an Aerial (or LNB on Dish) will increase the Intensity/level, but slightly reduces the "quality" according to the NF and IM3 figures. Thus a bigger aerial (or Dish) will greately improve quality AND signal level/Intensity, but an amplifier will not.


  • #3
    CHW
    Closed Accounts Posts: 136 ✭✭CHW


    Will a STB use more power at lower quality percentages? (More CPU processing?)


  • #4
    gtg60
    Registered Users, Registered Users 2 Posts: 1,759 ✭✭✭gtg60


    Very informative and knowledgable answer, thanks.
    watty wrote: »
    If the Intensity/Strength is over 80%, sometimes the signal quality will improve with a 6dB attenuator on the tuner input, but unless the quality is below 45% you would not see any difference.

    If my Signal intensity ISN'T over 90% then I just don't get an artefact free picture.


  • #5
    watty
    Registered Users, Registered Users 2 Posts: 32,445 ✭✭✭✭watty


    CHW wrote: »
    Will a STB use more power at lower quality percentages? (More CPU processing?)

    no


  • #6
    watty
    Registered Users, Registered Users 2 Posts: 32,445 ✭✭✭✭watty


    gtg60 wrote: »
    Very informative and knowledgable answer, thanks.



    If my Signal intensity ISN'T over 90% then I just don't get an artefact free picture.

    Then you may have a lot of local interference.

    Also the bar/level displays vary hugely from setbox to setbox and not related to exact quantities as on test gear.

    I'd bet if you reduce Intensity by 20% at the actual setbox input it doesn't add artifacts (i.e. Aerial has signal that would be measured at 90% still)
    .


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  • #7
    gtg60
    Registered Users, Registered Users 2 Posts: 1,759 ✭✭✭gtg60


    watty wrote: »
    Then you may have a lot of local interference.

    That's more likely the answer, I can pick up Three Rock and the Greystones Relay where I am and it is very difficult to actually get a very clear Analogue signal, either way I'm happy now as I have a perfect Digital reception.


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