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TV Signal Interference with HDMI Cable

Discussion in 'Freeview Forum' started by Telephonewire, Jun 15, 2010.

  1. Telephonewire

    Telephonewire Member

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    From a previous thread...

    The problem is that whenever I plug my PC into one of the HDMI sockets the TV signal deteriorates significantly to the point where it renders watching TV impossible. I'm sure that it isn't a coincidence as I've plugged and unplugged the HDMI cable many times and the TV signal always deteriorates and when it is plugged in and recovers as soon as I unplug the cable. It happens no matter what HDMI socket I use on the TV but doesn't happen if I use the PC input.

    From me...

    Hi, I am getting exactly the same problem; I only discovered it by chance. With the signal strength meter displayed on the screen I played around with all the cables and each time I pulled out the HDMI cable from my PC then the signal returns to a constant strong level. With the HDMI cable plugged in the signal is fluctuating up and down all the time causing the picture to constantly break up every few seconds.

    If I swap the HDMI cable from my PC to the TV with a 15 pin D-Sub cable the problem instantly disappears. However, the crispness of the picture quality has now also disappeared (as the D-Sub uses an analogue signal rather than the HDMI's digital signal).

    Any help on resolving this issue would be gratefully received.
  2. grahamlthompson

    grahamlthompson Well-Known Member

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    It's a poorly screened hdmi cable. Strangely the cheaper ones seem to suffer less from this problem. Try another cable.
  3. Telephonewire

    Telephonewire Member

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    Hi Graham,

    Thanks for your quick response.

    Are you sure about this or is this just an educated guess? It's just that it is very easy to blame a low quality cable for interference because it seems so obvious, however, the cable appears of high quality etc. and I would be surprised if it were so poorly made given the fact it was made for HDMI transmission?

    How could an HDMI cable cause the TV signal, which travels along a completely independent screened coaxial cable, to deteriorate when plugged into the TV? Then when I pull the HDMI cable out of the TV it goes back to normal?

    When I pull the HDMI cable out of the TV, only a few cms from the TV socket, the interference completely stops; surely if the HDMI cable was badly screened then the interference would continue with the cable unplugged but essentially in the same position relative to the coaxial cable etc.?

    I was thinking along the lines of a badly grounded earth wire in the HDMI cable from the PC or possible a voltage on the earth wire when it should be at zero volts so when plugged in it causes some sort of interference etc?

    Thanks.
  4. Gavtech

    Gavtech Administrator

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    This is a well known problem.

    When you remove the HDMI cable the HDMI interface shuts down altogether.

    The cable radiates frequencies in the UHF band similar to those used by the Freeview transmission channels. [ Actual frequencies are dependent on resolution settings so different settings produce different results ]

    Depending on which part of the country you receive in, and therefore which frequencies the various muxes are broadcast on, the resultant interference can wipe out some or all of your muxes.

    The remedy is as Graham has said above. Try another HDMI cable.
  5. Telephonewire

    Telephonewire Member

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    Hi Gavtech,

    Many thanks for your advice; I will buy another cable and give this a try.

    One last thought though.... the PC is placed under the TV about 30 centimetres lower on a shelf.

    If the general HDMI circuitry, within the PC, is throwing out a load of interference then it could be that interference that is being picked up by the coaxial cable rather than radiation from the HDMI cable itself; in which case swapping the cable won't make any difference.

    I guess I won't know until I give it a try...!

    Regards.
  6. Rodders53

    Rodders53 Active Member

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    I'd certainly try relocating the PC and cable(s) to see if it is a proximity issue.

    My first Philips CD player could NOT sit on top of my tuner-amp, but was happy alongside it (due to inadequate RF shielding on both items) c.1984 btw.

    Good quality double-screened aerial inter-connect cables (rather than the thin white supplied variety) may also help.

    Different hdmi cables will have different effects. Don't spend a fortune - ebay cheapies are probably just as good.
  7. Kanny Ken

    Kanny Ken Member

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    I beg to differ on the cause of this intereference even though digital signal processing hass never been my forte.

    I have just bought a Sony KDL40EX503 TV and connected my Sony RDRHXD870 HD/DVD by HDMI lead. I also have Sky+HD box connected to TV by HDMI. When the 870 HD/DVD is powered on then the BBC Freeview channels are lost on the TV plus sundry other channels. ITV channels still fuction. If the units are connected by SCART all channels can be tuned but then I lose HD quality on the Sky box.

    Yes, it is a problem with HDMI connections but not as simple as radiated noise from a cable. If I remove the 2 aerial leads from the back of the 870 HD/DVD and connect them together then my TV can then get all the usual Freeview channels. So, all that I change is connect the TV aerial socket directly to the wall rather than via the 870 HD/DVD. All the cable routing is unchanged so it it were noise from a poorly screened cable I should still see it. If it is noise then it is generated within the 870 HD/DVD when the HDMI connection is made. Might be an earth loop so maybe I will try breaking some eaths on the coaxial cables.
  8. Kanny Ken

    Kanny Ken Member

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    Partly by luck when fumbling around trying to unplug cables, I discovered the fault varied as different channels became good and bad. To cut a long story short, it was all down to the aerial lead from the wall to the 870 HD/DVD. It was a relatively new one from one of the sheds, can't remember which one, but felt loose in the socket. I found an ancient half-homemade cable last used years ago and replaced the new one with it. All Freeview channels now work on both the TV tuner and the HD/DVD tuner.

    Moral of the story is, aint technology wonderful and don't throw anything away!

    And P.S. there is a lot of BS spouted about HDMI cables, try to ignore it and look for the simple solution.
  9. Gavtech

    Gavtech Administrator

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    You've missed the point here.

    The cable you have discarded was obviously exhibiting a weakness to the radiation from the HDMI cable.

    Both sides of the equation need adequate screening.


    A well known, well documented, frequently occurring problem, most certainly does not amount to B.S.
  10. Kanny Ken

    Kanny Ken Member

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    I maybe cut the story too short because you are missing the point I tried to make. I re-routed the orginal aerial cable so it was well away from from the HDMI cable and the problem if anything got worse. The HDMI cable remained in the metal channel of the shelf unit, which as it is firly bolted to the wall, at the frequencies your must be talking about, can be considered well and truly earthed so the shielding of the HDMI cable was very good. I previously mentioned that the aerial cable felt loose in its socket and from my long experiences of coaxial cable carrying small signals, i know how tempermental it can be; even a soldered joint that has apparently good connection can create noise. Any dissimilar metals in contact can generate a potential difference and if the contact changes, the voltage changes and hey presto, you have noise! Trust me, I can bore for England on the subject after a career in scientific instruments.

    Recently, I installed a digital TV in my mother in law's kitchen to replace an ancient analogue set that had worked perfectly for years. So what happened, the ITV channels at the high frequency end of the Freeview spectrum were all over the place. Again to cut a long story short, the solution was cut off the old connector that felt loose in the TV aerial socket and replace it with a cheapo connector from B@Q and it now works perfectly.

    So I rest my case!
  11. Kanny Ken

    Kanny Ken Member

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    So when my wife saw me fix the lost channel problem on our new TV and knowing I had sorted a similar problem on her mother's TV she said "Now what about fixing the TV in our bedroom?"

    I tried to explain it was a different porblem but who am I to ignore "she who must be obeyed"

    The problem goes back some time and is a loss of the ITV and other channels at the high end of the spectrum. However, there has been much in our local media about transmitters problems as they prepare for the digital switchover. Apparently they switched off our main transmitter and temporarily replaced it with a shorter mast using less power but neglected to tell the public. So many people have had problems with ITV but been told by opportunist engineers they need a new higher-spec aerial costing around £300 and the have fallen for it. Eventually the cat was let out of the bag about the surreptitious transmitter work and folks are not best pleased. To rub salt in the wound, the main aerial which is well overdue for being back in action, did a fair impression of a megasize roman candle during tests and was totally destroyed. So the earliest we will have full power transmission is now September.

    The aerial for our bedroom TV is one of those compact electronic antenna with built in amplifier. It worked well at first and as it looks well made and came with decent cable thus I assumed it was pukka kit. So believing that and knowing of the transmitter farce I thought it was futile to change the UHF coaxial connector but knew unless I did, I would be continually reminded of it.

    Well, I hacked off the original moulded connector from the aerial lead and replaced it with a Ross alloy connector from Robert Dyas (About £2.70 for a pack of two). It is solderless, you clamp the central conductor with a screw. Now all the channels are back!. Las night signal strength on ITV1 was 61% with quality all over the place as the picture and sound broke up. Tonight signal is 62% but quality usually 100% with an ocasional dip.

    So that is three out of three problems with Freeview tuning cured by replacing UHF connectors. I now wonder how many people who bought new aerials could have benefitted from such a cheap solution!
    Last edited: Jun 16, 2010
  12. nvingo

    nvingo Active Member

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    Well done. That amounts to the advice to try replacing a cheap flylead with one self-made using proper coax cable and metal plugs, often posted when people report signal problems on just some receivers.
    Just that when a new HDMI device added to the mix affects signal, it may not be the total cure.
  13. igglepiggle

    igglepiggle Member

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    agree gavtech - and still no solution from the manufacturers !
  14. Hallucyn8

    Hallucyn8 Member

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    Hi guys

    I'm new here but came across this thread as I am having a very similar experience.

    A while ago I bought a DVI to HDMI cable to connect my PC to my Sony LCD TV. As soon as this was connected it totally killed the Freeview signal to both the internal tuner in the TV and the tuner card in the PC. I put it down to a dodgy cable, got rid of it and went back to using a VGA cable (with a DVI to VGA converter).

    Recently I decided to try again and bought a new DVI to HDMI cable. Plugged it all in and everything worked brilliantly for about the last 3 weeks. Then literally overnight the problem has returned. I was watching a Freeview channel on my TV last night while the PC was recording another show and everything was working perfectly. This morning I try to do the same and no signal to the PC or the TV. Unplugged the HDMI cable from the TV and the signal returns, plug it back in and the signal disappears.

    I can see that there is obviously a known issue with HDMI and Freeview interference but what I can't work out is what could suddenly cause this to happen when everything had been working fine for weeks.

    Any thoughts on what could have caused this and wether there is anything I can try apart from buying another new DVI to HDMI cable?
  15. grahamlthompson

    grahamlthompson Well-Known Member

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    Could be a poor screen connection on the coax patch leads. Best to make your own using sat grade coax. If you have the thin white ones stick them in the bin :rolleyes:
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  16. Gavtech

    Gavtech Administrator

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    Welcome to the forum.


    Is it possible there has been any resolution setting change? [ Either manually or automatically ]

    Changing the resolution changes the frequencies going through the HDMI link and can be the difference between UHF problems and none.

    Other than that, or cables being moved relative to each other I can think of no cause other than screening failures either in the UHF system as mentioned by Graham above, or in the HDMI lead itself.
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  17. Hallucyn8

    Hallucyn8 Member

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    I'm not sure of the quality of the patch cables, they're not "thin white ones" but I don't recall spending much on them when I bought them.

    There hasn't been any resolution change as it is a set resolution on the PC.

    The cables are unlikely to have moved much although I couldn't rule it out as I do have an optical switcher round the back of the TV which I have used last night and this morning.

    Just off out now but I will have a play around with the cables later and see if it makes any difference and failing that I guess I will have to start replacing cables.

    Cheers for the suggestions though
  18. AndyDerv

    AndyDerv Member

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    Or by calling out an honest aerial installer ?

    I`ve never knowingly sold an aerial to any customer who simply required a new connector or lead. In fact, I`ve quoted £100+ for an new aerial over the phone, then turned up to do the job and only charged £25 to replace a lead.

    Although I haven`t read every post in this thread, I get the idea that some people have problems with Freeview caused by HDMI useage. The obvious answer is to make sure that all coaxial leads in the system are fully screened. The less obvious answer is that the screening in the TV itself might not be so clever.
  19. nvingo

    nvingo Active Member

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    Just a thought there...
    My PC and TV are connected by VGA.
    If I turn the PC on, by the time it reaches the Windows Login screen it will have interrogated the display to determine which resolution to use.
    My display is full HD 1920x1080.
    If the display's power switch is left in the off position, interrogation fails and the Windows selects a lower resolution (in this case with pan/scan enabled).

    Just saying, check the power-on order ;)
  20. Hallucyn8

    Hallucyn8 Member

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    A quick update...

    Bizarrely when I came to look at the problem again later that day everything was working fine. The problem returned however, although not as bad, after moving all my equipment round as I had bought a new TV stand.

    I have got to the bottom of the problem though. All the cables from the back of the TV are routed through a cable management "clip" on the back of the TV. The coaxial aerial cable and the HDMI cable where right next to each other. I rearranged the cables so that were other cables in between these two and the problem has gone.

    This would confirm interference between the two cables being the problem although presumably there is not too much interference if moving them apart slightly resolves the problem.

    Cheers again for your help and suggestions
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  21. Gavtech

    Gavtech Administrator

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    I'm pleased you've nailed it down. :smashin:

    Thanks for reporting back your solution.
  22. opsking

    opsking Member

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    Hi. My long amplified HDMI runs are radiating RF interference that my Universal Remote Powerblaster MRF100B picks up. HDMI cable is "PTC 100ft 24AWG Premium GOLD Series HDMI Amplified Cable" from Amazon. When I unplug the cables the interference, which is visible as a quickly flashing Powerblaster status light, stops.

    Thanks to this thread, I will try grounding (earthing), shielding and/or re-routing these long cables away from Powerblaster to hopefully reduce or eliminate the interference. This is the first problem I've had with these extra-long amplified cables. Hopefully I do not have to replace them.
  23. Clem_Dye

    Clem_Dye Member

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    I always make my own co-ax aerial cables using double-shielded cables and metal plugs. Some of these cables run alongside cheapie Amazon Basics HDMI cables. Thus far, no problems that I'm aware of. The cost is a little greater, and you have to factor in your own time in preparing the co-ax cables, but you do get exactly the right length of cable every time.


    Clem

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