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  1. Hi,

    I would like to know if somebody knows what happen when satellite signal strength is too high for a capture card.

    I wonder what collateral effects are.

    I hope somebody could help with some notions about the bad effects.

    Regards,
    Mapg
    Last edited by mapg; 19th Nov 2015 at 03:05.
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  2. Mod Neophyte Super Moderator redwudz's Avatar
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    What format are you using for capture? What program/software/hardware and setup? Without that, not many suggestions.

    But, even if the signal strength is too high, the capture device/program should notice and hopefully suggest a solution.

    OK, overdriving a video card if it isn't able to cope, could result in probably blown out whites, muddy blacks and a lot of noise. Just a guess.

    Depending on the card inputs/outputs, there are simple attenuators that can reduce signal levels.
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  3. Thank you redwudz for your help.

    Well, actually it is not a capture card but a DVB to IP gateway where I take the video/audio signal to be encode by ffmpeg via UDP protocol.

    I wanted to know what the typical bad effect when satellite signal strength is arriving to the gateway too high. This is because I would like to recognize and identify them as distinctive of signal strength too high.

    Sudden high noise in the audio and video, pixelation? etc.

    What's your experience in this kind of situations?

    What is the origin of these kind of issues (too big satellite antenna??, wrong LNB??)

    And what's the best solution to mitigate the effects lowering the signal strength? filters, what filters? splitters, what splitters?

    Thank you very much in advance.
    Mapg
    Last edited by mapg; 19th Nov 2015 at 03:14.
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  4. Originally Posted by mapg View Post
    Hi,

    I would like to know if somebody knows what happen when satellite signal strength is too high for a capture card.

    I wonder what collateral effects are.

    I hope somebody could help with some notions about the bad effects.
    There are two parameters describing digital signal (simplification for this problem) - level and quality - to low or to high level is not OK, quality should be always highest as possible (and unlike analogue signals there is no linear dependency between signal level and signal quality).
    When signal level is too high, internal Low noise Amplifier can be saturated and it will start clipping signal i.e. quality will drop significantly.
    Usually FE LNA's can deal with wide signal dynamics but if you use pre-amplifier they can be saturated.
    If your signal have to high level but his quality is high then you can use dedicated signal attenuator (dedicated for satellite network) - there are fixed and variable attenuators.

    Symptoms of the bad signal are same for too low and too high levels - you can distinguish between those by observing level value and quality value.
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  5. Member
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    You need to reduce the signal strength received into the dvb unit ... what arrives at the gateway is a non issue.

    High signal but what is the quality level ?

    Signal strength which exceeds standards or recommended broadcasters guidelines can cause DVB unit to lock frame / black out ... this is not a nice way to look after equipment and while they can handle it the device will develope issues.

    Easiest way is to turn the antenna 2 to 5 degrees off center line from source position which will lower the signal strength.

    Here's a uk write up on too much signal and how to rectify the problem
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  6. Thank you for your help. I have a better idea now about what happen when satellite signal strength is too high.

    I have to convince the tech guy to add these signal attenuators.

    For now I have the following arguments:

    Signal strength too high ...

    1) ... can cause DVB unit to lock frame / black out.
    2) ... can damage the equipment (Bjs said: "this is not a nice way to look after equipment")
    3) ... device will develope issues.
    4) ... internal Low noise Amplifier can be saturated and it will start clipping signal (i.e. quality will drop significantly).

    If you have more ideas, please go ahead and drop here some line.

    Thanks you very much!
    Mapg
    Last edited by mapg; 19th Nov 2015 at 08:15.
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  7. You are in US or Europe? DVB suggest Europe but...

    Use Nordig standard where some guideline signal level values are provided, ask technician what signal level is measured, compare this with Nordig. If signal level is too high then attenuator need to be introduced.
    http://www.nordig.org/specifications.htm
    Based on Nordig you should expect:
    3.2.7.2 Signal Level
    The satellite NorDig IRD shall accept input signals with a level in the range -25 to -60 dBm, and
    demodulate the signals with a performance as specified in section 3.2.8.
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  8. Thank you Pandy for your help.

    DVB gateway already inform about the correct margins. It's similar to what you mentioned.

    Specifically they are ...
    -75dBm ~ -25 dBm (namely 34 dBuV ~ 84 dBuV).
    Currently there are tuners receving 109 dBuV (25 dBuV more than upper limit). Because of that I decided to ask in this forum.

    Some comment about it?

    Kindest regards,
    Mapg
    Last edited by mapg; 19th Nov 2015 at 11:44.
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  9. Originally Posted by mapg View Post
    Thank you Pandy for your help.

    DVB gateway already inform about the correct margins. It's similar to what you mentioned.

    Specifically they are ...
    -75dBm ~ -25 dBm (namely 34 dBuV ~ 84 dBuV).
    Currently there are tuners receving 109 dBuV (25 dBuV more than upper limit). Because of that I decided to ask in this forum.

    Some comment about it?

    Kindest regards,
    Mapg
    Well - from my perspective this kind of levels (above 85dBuV) are out of any standard and seem that some amplifier (line/distribution type) is involved - most of cable standard limit signal level in customer point to 75dBuV - i would use 20 - 40dB fixed attenuator (at least) to reduce signal level.
    Are You sure that this is satellite not terrestrial/cable (DVB-T/DVB-C) signal?
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  10. Thank you Pandy for your opinion.

    Yes, you are right. Such value is a strange thing.

    I have been told that 109 dBuV is not a real value, but DVB gateway is just alerting that signal strengh is too high and is using such value as a mere reference. Like alerting that something wrong is happening.

    Yes. It's satellite signal.

    Thanks again.
    Mapg
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