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Thread: Inverter Interfering with DSTV signal

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    Question Inverter Interfering with DSTV signal

    Hey guys,
    I am a registered sparky and do many inverter installs at the moment.
    I have come across something today which has totally puzzled me. I will get to the bottom of it as I refuse to walk away from anything without a solid answer.
    But, maybe one of you guys has seen something like this before...?
    I installed a modified square wave inverter today at a clients house.
    It's a 360W unit and i have installed many of these before with no hassles whatsoever.
    Its just a stand-alone unit by the tv with a battery and a multi plug with tv, dstv, etc connected.
    Set it all up and turned off the plug supplying the mains to the inverter to test it, and, what usually happens is the slightest of flicker on the screen (usually not even noticeable) and the channel continues as though nothing has happened.
    All good.
    Well, today when i turned the power off, the tv stayed on, the decoder stayed on, but the signal disappeared!
    I thought that maybe i had left something off of the inverter multiplug that was supplying power to the satellite install.
    So i checked again, and found nothing the matter.
    Turned the plug back on to supply mains power again, and within a few seconds the channel was playing again!
    The satellite system has a PVR decoder, and an old dstv box as the Xtra view decoder and this is supplying the bedroom and kitchen tv's. There is also an LNB multi switch unit which supplies 2 inputs and 4 outputs to the 2 decoders.
    Well, switched power off again and noted that both the kitchen and bedroom continued to be supplied with a perfect signal and could change channels no worries.
    Just the lounge tv supplied by the PVR was affected!
    I checked all the satellite cables and redid the connections and still no joy! As soon as inverter kicks in signal disappears from PVR but still perfect on older decoder!!
    I had to leave to get to another appointment so I will be returning there tomorrow to fault find further.
    My thinking is that the inverter is putting out some sort of electro-magnetic interference which is disrupting the PVR circuitry somehow?!
    Although it is not doing any damage to the old dstv decoder at all. This leads me to believe that it cannot be the multi switch unit either.
    Very strange indeed!
    I have installed loads of these smaller 360W and 600W inverters as stand-alone packages, and have never come across this problem before!
    Granted i cant say whether i have installed this package near another PVR decoder, as it has never occurred to me to check, as this would never have entered my head as being a problem before today!
    What i will try tomorrow is to move the inverter and battery to the other side of the room to negate electrical interference and then run an extension lead to supply the tv installation to see if this solves the problem.
    If it does then i know that i need to install in the adjoining cupboard and screen the sides of the cupboard to prevent this happening.
    If it doesn't solve the problem then i would have to say that the PVR 2P decoder (which is not supported by dstv anymore) must be the faulty device, or at least the culprit, as it does work on mains power!
    I could no doubt install a pure sine wave inverter but this negates the idea of supplying a cheaper option for my clients.
    Anyone else come across this before??
    Simon

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    Diamond Member AndyD's Avatar
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    I'd also start with physical separation, put a few meters between the decoder and the inverter. If that doesn't help try plugging another appliance into the inverter and plug the PVR back into a normal socket see if it still interferes with the PVR decoder when the inverter goes into power fail and the PVR has normal Eskom supply.

    If it's an old decoder with the old antenna coaxial socket in the back it's possible there's some kinda internal earth referenced electronics, if the inverter has a floating neutral or isn't connecting the earth to the decoder it might be playing havoc. Maybe a long shot but try running an extra earth to the decoder if it's feasible.
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    Gonna try the separation first and see if it helps. Interesting if it would interfere when plugged into mains and the inverter runs next to it...will check that out.
    Might try the earth idea too as its not a big hassle to connect an earth lead from the plugs earth point for testing...
    A very strange one indeed, but i will report back once i've figured it out so others might learn from this experience.
    One way to take a quoted job and turn it into a huge loss of man hours, but if i learn something from it then it hasn't been a total waste

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by deejaypsy View Post
    One way to take a quoted job and turn it into a huge loss of man hours, but if i learn something from it then it hasn't been a total waste
    The school fees never end
    The trouble with opportunity is it normally comes dressed up as work.

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    Diamond Member AndyD's Avatar
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    Lol, as Dave says the school fees just keep on coming.

    I'd be interested to know what you find as well so please let us know.

    Oh...and good luck.
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    Quote Originally Posted by AndyD View Post
    Lol, as Dave says the school fees just keep on coming.

    I'd be interested to know what you find as well so please let us know.

    Oh...and good luck.
    As for the school fees, that's ok. Its part of the game hey?

    As for the inverter story, it's looking like a problem with the dstv PVR 2P unit.
    I tried running an earth to the unit and testing it on inverter power to no avail.
    I then tried physically moving the inverter and battery to around 10m away from the unit and it still lost signal while the other decoder worked flawlessly under inverter power!
    My only possible conclusion to this is that the square wave emitted by the inverter creates some sort of electro-magnetic interference, which is causing problems with the signal decoder chip in the PVR unit itself thus the loss of signal.
    It is the only thing that it can be. Perhaps this is one of the reasons that dstv has discontinued the model? Although i suspect it's more for regulation of the intended use of their product purposes!
    I suppose that a pure sine inverter might not give this problem, but the client does not wish to go down that route because of expense. They are away on holiday for a month now, and will be purchasing an Explora so that i can complete my install, on their return. So i will update this thread when that happens, as to the functioning of the system with the new Explora installed
    I did an install of an exact same 360W inverter unit at a house yesterday morning, and the client had a dstv Explora unit within 1m of the inverter. I was very interested to see if it would work. It did. Perfect changeover to inverter supply. Not even a flicker on the screen!
    So, there it is....if this helps anyone else in the future, then I've done my bit for the forum for today!

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    Diamond Member tec0's Avatar
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    A PVR system is essentially a computer running a central processing unit and random access memory along with your decoder there is the dish feed. Ok for any person not knowing earth is very important for a decoder or it will lose signal. Yes most decoders run on two point plug with a wire earthing it to a plug separately. Depending on your wiring you may have a earth problem in the area. Given that you are a qualified sparky you know better then me so finding it will be no problem.

    EMI will effect your decoder as essentially it is messing with the wave length of both your signal and power signal at the same time. When running your inverter are you driving any motors? Motors tend to mess around with frequency on inverters hence why some inverters have a setting for motors and a setting for electronics. I know that my inverter i can only run electronics OR motors not both not in combinations?

    Sorry i cannot be of any more help.
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    Morning Tec0,
    I did try earthing the decoder but it did not help the situation.
    The puzzling thing is that the old style decoder works a charm, but the newer (also old now) PVR 2P decoder loses its signal.
    Its certainly nothing to do with the dish or any of the cabling as the older decoder doesn't lose signal even for a second.
    The older decoder also does not have an earth lead attached to it at all. It has a standard figure of eight 2 wire supply cable with no adapter in the mains lead. So a straight 230V is supplied to the decoder and no earth at all. I assume it picks an earth up from the satellite cabling? Although if the dish isn't earthed i would have no idea where this earth comes from either??
    I have not done a loop test on the installation so i cannot tell you how good the supply earth is, but that really should not matter in the slightest to the dstv signal, as when it's running on mains there is no problem with the signal...and the fact that the older decoder doesn't skip a beat...
    I can only assume the square wave is outputting an interference (which is totally plausible), although why it affects the PVR and not the older decoder baffles me. Surely they make these pieces of equipment a bit more robust, especially nowadays when nearly every piece of electronic equipment we have either has wifi and sends and receives signals, or gives off at least some interference...?
    Anyhow, i know from another install, as mentioned, that bthe Explora does not have this issue, so when the client returns from holiday, I'll reconnect and post back here the results (which i am pretty certain will be favourable).

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    Diamond Member tec0's Avatar
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    Well this is how earthing is done, as you can see the block on my very very very old decoder is clearly marked. My inverter runs with a modified sine wave out put is 230V at 50Hz i have no problem at all with my DSTV

    Click image for larger version. 

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    Quote Originally Posted by tec0 View Post
    Well this is how earthing is done, as you can see the block on my very very very old decoder is clearly marked. My inverter runs with a modified sine wave out put is 230V at 50Hz i have no problem at all with my DSTV

    Click image for larger version. 

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    Morning Tec0,
    This is exactly how i earthed the PVR 2P with still no luck at all on inverter.
    The old decoder in their Xtra view setup, is exactly the same as yours in the picture...it has no earth connected to it and still runs perfectly in inverter mode.
    Hence my thoughts towards the PVR being the problem in this equation...
    We are not human beings undergoing a spiritual phase.....we are spiritual beings undergoing a human phase....

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