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Thread: DVBS2 Severe Pixelation Intermittent Issue, Signal levels good, clear line of sight

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    Default DVBS2 Severe Pixelation Intermittent Issue, Signal levels good, clear line of sight

    Hi Members,

    I'm new to this forum. I have been installing residential satellite systems for more than 3 years and have done a small amount of MATV and commercial installation. I have an issue that totally eludes me and would welcome any suggestions!

    It's at a commercial premises, 80cm hills dish (from memory, it's been a while since I've inspected), it had a new sharp twin LNB a while ago, has some inline coax powered amps (which I've only seen a photo of so far, I'm guessing there is no power at their location), this runs into a comms/equipment room where there are 2 splitters and 2 separate 8way multi-switches to give 16 outlets (long story why it's not just a 16 way). This runs into 1 sky box, 5 Mystar2 (HD) boxes and 1 Fox IQ2 (HD) box. The Fox and MyStar are tuned to HD channels and going into HD modulators via HDMI.

    Signal levels are good. In fact I have attenuated before the splitters 6db to ensure I'm not over-driving the tuners. Signals on the DVB-S2 transponders are around 75-76 DCP, 16MER and post BER better that 10E7. The dish is secure and there is absolutely clear line of sight. The dish is around 30-40m from the comms room where the multi-switches and set-tops are located.

    I have witnessed the pixelation issue occurring with Mystar/Foxtel both post-modulator and via HDMI to a HD monitor, on previous visits. Issue mainly occurs when fast movements occur in the broadcast, like in football games. It certainly doesn't look like typical low signal pixelation and freezing. Today I had trouble replicating the fault. Then, this evening the venue manager called me and sent me a video showing very bad pixelation. I've been told by the manager that "it seems to be weather related" (although he couldn't tell me the type of weather) and that the issue comes and goes. The issue has only been a problem since they moved from a SD system to HD system, hence must be DVB-S2 transponder related. I've proven it's not Mystar related by installing the IQ2 today. I've also proven it's not modulators as it still occurs on HDMI to a monitor.

    Any suggestions as to what to investigate next would be very much welcomed. I haven't seen an issue like this before, even in some buildings that have some pretty poorly designed and maintained systems.

    Here's a few thoughts I had:
    - I'm wondering if there could be some sort of interference? Wifi? Power line? Mobile/Broadband? The venue is a club and I'm wondering if more patrons = more devices = more interference? There are a couple of open terminations on the multi-switches, I really should have put a terminator on them.
    - Something intermittent with the in-line amps?
    - Is there any type of filter I could try?
    - I'm not fully up to speed on differences between DVB-S and S2, I did think everything was supposed to be backwards compatible, but could there be some old components in the system that are not up to the task?
    - There is Rutherford airport nearby, however that is not a commercial airport, more for training and amateur pilots, so I can't imagine it causing an issue that can last for several hours. There is also an air services facility at nearby Gillieston heights, not sure what it does, but it clearly has antenna arrays. Any chance there could be some sort of interference? I think this is a really long shot as there would be heaps of complaints from Foxtel customers in the subdivisions that surround that area.

    Any suggestions or ideas would be very much appreciated.

    Thanks,

    Tony



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    Hi Tony,

    I'll move this to the Satellite General section (as it's not network related).

    As you'll appreciate, without being there with test equipment, I can only go by the info you've provided.

    There's a few things that don't sit right with me for an SMATV system.

    1. Size of the dish and cabling distance to the distribution location.

    An 80cm dish doesn't even comply with Foxtel standard for commercial installations.

    Especially with long cable runs, you should probably be using a 1.2m dish and RG11 Quadshield cable to the distribution point.

    2. Use of inline amps.

    Why?

    If signal levels are too low, it will likely be dish size is too small and/or there are excessive cable losses.

    What size cable has been used, RG6 or RG11?

    Inline amps are typically inherently noisy and should be avoided wherever possible.

    If they are being used to compensate for losses.... fit a larger dish and get rid of them.

    3. Splitters used, instead of a larger capacity multiswitch, or cascadable smaller multiswitches, eg: 2X8-Way cascaded.

    Pixelation of fast-moving objects are more likely compression of the broadcast transmission/recording, rather than received signal.

    To a lesser extent, displays may also have an issue.

    Have you checked if this pixellation is occurring on all screens?

    Can you meter record Reed–Solomon levels?

    BER/MER often can't detect very fast transient glitches experienced with some types of interference, so being able to 'see' dropped packet figures is extremely helpful locating these types of issues.

    The signal figures you've quoted sound fine, so I'm actually leaning towards the pixellation being either the fault of the broadcast, or the displays. (Make sure the displays have the latest firmware).

    From what you've described, it sounds like more of an 'image' issue, rather than a signal issue.

    How are all the modulators being combined?

    If terrestrial FTA also being mixed with the modulated decoders?

    What modulated distribution platform is being used... DVB-T? IP?

    What distribution amps are being used?

    Interference is possible, but not generally experienced with Ku-Band, but I have seen some 4G interference if located close to a cell tower.

    Interference is more likely to be getting into the distribution side of things.

    'If' there is any interference being picked up by the dish/LNB, those inline amps will be amplifying it as well.... again, ditch those amps, regardless.

    DVB-S2 is certainly more fickle that DVB-S... all the more reason to capture more signal at the dish to begin with.

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    I've seen satellite TV signal losses occur in clubs before, and also couldn't work out why. Especially when loud bass music is played and the ground/walls vibrate(s) a little.

    Also, like mtv said, the inline amps and then subsequent attenuation devices - kind of redundant?

    And, agreed, can never go wrong with a bigger size dish. Most amps amplify noise too anyway, so no real gain in signal quality, more just in signal strength (which includes noise). Also, the fewer breaks there are in the cable feed (e.g. amps, attenuators, splitters, switches, etc.) the better. If something doesn't really have to be there - take it out.

    I've had pixellation and funny decoder behaviour happen before from something as seemingly innocuous as a f-type joiner barrel where I just wanted to make the cable longer by joining two lengths.

    Double-screened coax (two layers of "foil" inside) will also help keep out any potential interference. Maybe even run the cable on it's own path, without other cables running next to it.
    Last edited by irritant; 26-05-17 at 10:36 PM.

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    Quote Originally Posted by AdrianR View Post
    Double-screened coax (two layers of "foil" inside) will also help keep out any potential interference. Maybe even run the cable on it's own path, without other cables running next to it.
    The standard in Australia for many years is quadshield (4 layers... 2 foil and two braid).

    Usually interference gets in via other means as the cable shielding is very effective.

    Electrical impulse noise can still be carried on cable shields though and long cable runs make good inductors for electrical noise.

    Coax cabling has minimum segregation distances from power cabling, but installers don't always comply.

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    Thanks heaps MTV and Adrian,

    Original dish, cable run and in-line amps weren't done by me. I've only seen the cable at the dish and comms room, it looks like tri-shield to me. Also. it's only RG6, most longer runs like this in commercial jobs should have RG11. Sounds to me like I should inspect the entire cable run. From what I gather the in-line amps aren't necessarily as close to the dish as they should be, so chances of amplifying interference are possible. I just checked a mobile phone tower map and found there is a Telstra/Optus/Voda 3g/4g tower across the highway, probably about 100-200m away, also hints to my theory that more patrons = more devices in the club = more transmissions from that tower.

    I'm also contemplating, I may be able to move the dish to a closer location then get rid of the in-line amps, the current location is probably a legacy of a number of renovations/extensions of the club. Then I'll also do a new cable run with proper segregation and no unnecessary joins. In fact, unless there is something weird with the building, I can't see why I couldn't get the dish directly above the equipment room.

    I haven't explored anything on the modulation side of things because the pixelation is happening when directly connected to the set-top via HDMI on my HD test TV, hence I need to solve that before I could prove any issues with modulation system.

    I'm also thinking I should check earthing of the system, If I add some earths to the new multi-switches, that should, in theory, earth the shield of the entire system. As I think about it, I suspect the system isn't earthed properly at all at the moment as those in-line amps probably aren't earthed and I can't think anywhere else the system would be earthed. Also, thinking that if I relocate the dish, I can run a quad LNB and get rid of the splitters to the 2 multiswitches.

    I'll check out reed-solomon levels, thats something new to me. I only have a Rover Master STC, so possibly it may no do that. It also may not be responding fast enough to pick up fluctuations in signal.
    Last edited by Tone944; 27-05-17 at 08:36 AM.

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    I'm fairly certain I know the location of the club, but if it's the one I'm thinking of, the mobile tower will be close to due west of its location. (The old water reservoir site?)

    If that's the one, I doubt it's cellular interference.

    Your client mentioned it seems to be 'weather related'.... I doubt it's rain fade. Usually electronic components exposed to extreme temperature changes, which would be the LNB and those inline amps perhaps if the are in the ceiling.

    I have seen the odd LNB go faulty with similar symptoms.

    Intermittent solder joints expanding and contracting with temperature variations, or just components failing under the same conditions.

    If the issue is being seen directly on a monitor before modulators/distribution then that side is likely OK.

    Does the pixellation occur on ALL channels, where there is fast image movement?

    It really sounds like the issue is the program, not a signal fault.

    Perhaps it just happens to be they are watching a fast-paced sports program when there's a weather change.

    Keep us posted... I'll be interested to hear what you find and the fix.

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    Thanks again MTV

    I reckon we are talking about the same place. I didn't want to mention names to respect their privacy.

    LNB has been replaced in last few months (doesn't mean it's not faulty though), but the signals are too high and the issues seem to occur without too much of a significant change in weather. Those inline amps, and the cable run that may have had various modifications and extensions over the years, I think, everything is pointing to those. Not sure what change in temps the inline's might have, they could be exposed to air con ducting or roof sheeting, so I think that's a possibility.

    Pixellation does occur on all HD channels when there is fast image movement. I looked at the same channels at a different location at the same time as it's been reported by them, so I'm pretty confident it's not due to transmission.

    My next step was going to be to see if I can relocate the dish closer so I have a short new cable run without amps. If thats possible it would be cheaper than replacing amps and solve multiple possible things at the same time. Even though we may then never know the exact cause, it should be solved. And if that doesn't solve it, then there really is a mystery!!!

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    If signal levels are too high, bypass the amps and see what you get.

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    How did it go Tone944? Is the problem sorted out?

    May be worth trying different HDMI cables too, just in case. Some brands are naturally better than others.
    Last edited by irritant; 21-06-17 at 05:59 AM.

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