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Splitters: interference on terrestrial from satellite box

[Deleted User][Deleted User] Posts: 351
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in Technical #1
Hi, I hope somebody can help me out there, please: I have a new house in France and decided to put in only a single coax cable to each room where I want the TV's. The wall outlets have decouplers to this single coax feed for both TNT (French digital terrestrial, like Freeview) and Freesat. I have absolutely no problem with the satellite/Freesat channels via my dish, but some of the French channels on TNT won't work at all or are badly chopped up if I leave the Freesat box on while watching digital terrestrial. If I switch the Freesat box to standby then after several minutes things curiously seem to settle down and I am able to watch French TV on TNT, but if I want to switch from Freesat to TNT straight away the only solution is to unplug the Freesat box from the mains. I have a strong TNT signal through the terrestrial aerial, and this is coupled to my satellite dish via an Axing SWE 4-01 coupler. I wasn't expecting this interference: it's not specific to the TV as I've tried other TV's and other wall outlet decouplers, but the problem persists. Can somebody please tell me if this is a standard problem with what I'm trying to do and so I have to live with it - or can I add an extra filter of some sort? - or is the problem the Axing coupler? Should I change it? Or is it the cabling? (...seems to be regular coax cable, it says "Class A 3GHz").
Many thanks in advance for any help.

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    albertdalbertd Posts: 14,360
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    #2
    It could be an instance of interference coming from an HDMI cable feeding the Freesat to the TV which ceases when you turn off the Freesat box. This a known potential problem and can be alleviated by making sure the HDMI cable is kept as far as practical from the TNT aerial cable(s).
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    [Deleted User][Deleted User] Posts: 351
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    #3
    Thanks AlbertD, I've just ruled this out as being the problem: I unplugged the HDMI cable completely and the Freest box still interferes with the terrestrial signal - so the Freesat box must be creating interference on the coax line: the problem goes away if I disconnect the Freesat box or disconnect its coax feed.
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    albertdalbertd Posts: 14,360
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    #4
    Oh well! At least that has narrowed it down a bit. Maybe someone else can come up with something.
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    chrisjrchrisjr Posts: 33,282
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    #5
    What are you using to split the signals back out again at the "TV" end of the downleads? Are you using the splitters designed for use with the combiner system or something else? The splitter should filter and isolate the TV and satellite outputs which a very simple one in two out splitter may not.

    Also have you tried a different satellite receiver? You mention you've tried other TVs but not an alternative satellite box. It is always possible there is a fault with the satellite receiver causing the problem so may be worth trying a different box if possible.
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    [Deleted User][Deleted User] Posts: 351
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    #6
    Hi chrisjr, thanks for the comments. My title to the problem is a bit wrong - sorry - I am using a coupler and decouplers, not splitters. For the decoupling, I've tried both the wall-mounted sockets (with three outputs, one for terrestrial, one for satellite, one for radio all on the same faceplate), and an in-line version, but they all behave the same. It's not the satellite box because I also have a second set-up in another room, and I get the same problem. Some terrestrial channels work just fine: it's TF1 and France 2 & 3 that are the main problem channels for some reason, and it's got worse since the day before yesterday when my local transmitter (Mount Ventoux) changed frequencies and got rid of the last of the analogue broadcasts. I almost have line-of-sight to the transmitter so I can't believe it's the signal strength.
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    [Deleted User][Deleted User] Posts: 351
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    #7
    chrisjr wrote: »
    Also have you tried a different satellite receiver? You mention you've tried other TVs but not an alternative satellite box. It is always possible there is a fault with the satellite receiver causing the problem so may be worth trying a different box if possible.

    Hi again & many thanks - you are right: it's the FreeSat box (a Humax HDR-1100S). I've just discovered that the box I have in the living room creates interference over the whole network, so having it on upsets the French terrestrial reception even on other TV's in other rooms. The other Freesat box I have in the bedroom, if left on, does not affect terrestrial reception. Will I have to get another box or is there a filter or something I can put in line to cure the problem, please?
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    anthony davidanthony david Posts: 14,504
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    #8
    Am I right in thinking that one coax carries UHF TV as well as the satellite signal? If so check the signal strength on the TVs with the satellite receiver disconnected. If the aerial signal is low then crosstalk from the satellite signal may be preventing reception despite using an appropriate wall plate. Under those circumstances you will have to investigate why the aerial signal is low. Although you say you have strong signal from your aerial you may also have a fault somewhere reducing its strength.
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    chrisjrchrisjr Posts: 33,282
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    #9
    Nick123 wrote: »
    Hi again & many thanks - you are right: it's the FreeSat box (a Humax HDR-1100S). I've just discovered that the box I have in the living room creates interference over the whole network, so having it on upsets the French terrestrial reception even on other TV's in other rooms. The other Freesat box I have in the bedroom, if left on, does not affect terrestrial reception. Will I have to get another box or is there a filter or something I can put in line to cure the problem, please?

    Swap the boxes round. That will confirm if it is the box or not. It could still be the splitter in the living room.

    If it is the box then it is likely it is faulty. There is no reason why it should be causing this interference. And it is unlikely that you can filter it out.
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    [Deleted User][Deleted User] Posts: 351
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    #10
    Thanks for the words of wisdom chrisjr. I just tried swapping them round, and the problem stayed with the box in the Living room - so it has to be the decoupler there. This is strange as I've already changed it for another one as a decoupler problem was my first port of call. Could it be something wrong with the cable from the coupler to the decoupler?
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    [Deleted User][Deleted User] Posts: 351
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    #11
    anthony david wrote: »
    Am I right in thinking that one coax carries UHF TV as well as the satellite signal? Yes. I'm not sure how to measure signal strengths per channel, but I presume the chains affected have lower strengths. I'm now thinking -along the lines that I have 2 problems, a combination of signal strength issues and a faulty cable or decoupler (see previous email). Many thanks for your help on this.
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    chrisjrchrisjr Posts: 33,282
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    #12
    Nick123 wrote: »
    Thanks for the words of wisdom chrisjr. I just tried swapping them round, and the problem stayed with the box in the Living room - so it has to be the decoupler there. This is strange as I've already changed it for another one as a decoupler problem was my first port of call. Could it be something wrong with the cable from the coupler to the decoupler?

    Actually neither of us are calling the device in the wall plate by it's correct name. It is actually a diplexer.

    The Axing SWE 4-01 device as far as I can tell is a unit that takes all four feeds from a quad LNB then feeds each out to a separate downlead at the same time combining a feed from a terrestrial aerial onto each output. ie Output 1 is a mix of LNB 1 and Terrestrial and Output 2 is LNB 2 and Terrestrial and so on.

    The wall plate diplexer then separates out the two signals by use of filters to ensure only satellite frequencies appear on the satellite socket and terrestrial signals on the TV socket.

    If you have changed the diplexer and get the same result then that does suggest it is not the diplexer. Most cable faults would result in a poor signal or no signal at all. And it is likely that the fault would be present whether or not the satellite receiver was there or not. But never a bad idea to check the terminations and make sure everything is neat and tidy and there are no stray strands of screen braid touching bits they shouldn't for example.

    It could also be the Axing SWE 4-01 unit. If you know which output feeds which room you could try swapping round the living room and another cable and see if the fault moves to the other room. If it does then it is something with the Axing SWE 4-01. Or it could be the LNB. So having found which cable does what, swap the LNB cables.

    For example. Say Output 1 on the Axing SWE 4-01 feeds the living room and Output 2 feeds the bedroom. Swap the cables on Output 1 and 2 round and see if the fault now occurs only when a satellite receiver is used in the bedroom. If it does go back to the Axing SWE 4-01 and swap LNB 1 and 2 round. If it is the LNB this should now put the fault back in the living room. If it is the Axing SWE 4-01 then the fault should stay in the bedroom.

    Doing something like that should narrow down what is at fault. It may also allow to to bodge a workaround by connecting the suspect Axing SWE 4-01 output or LNB input to a room that won't ever have a satellite receiver on.
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    [Deleted User][Deleted User] Posts: 351
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    #13
    chrisjr wrote: »
    The Axing SWE 4-01 device as far as I can tell is a unit that takes all four feeds from a quad LNB then feeds each out to a separate downlead at the same time combining a feed from a terrestrial aerial onto each output. ie Output 1 is a mix of LNB 1 and Terrestrial and Output 2 is LNB 2 and Terrestrial and so on.
    .....It could also be the Axing SWE 4-01 unit. If you know which output feeds which room you could try swapping round the living room and another cable and see if the fault moves to the other room. If it does then it is something with the Axing SWE 4-01. Or it could be the LNB. So having found which cable does what, swap the LNB cables.
    .... It may also allow to to bodge a workaround by connecting the suspect Axing SWE 4-01 output or LNB input to a room that won't ever have a satellite receiver on.

    Hi chrisjr, many thanks indeed, your long-distance diagnosis was spot on: I went through the swapping procedure as you suggested above and pinpointed the problem as being line 3 of the Axing box. I've just done the 'bodge' and put line 3 on a feed I only use for satellite and not terrestrial. I'm a happy bunny again :)
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