HDMI radiating interference

Discussion in 'EMC Matters' started by G4LNA, Dec 8, 2018.

  1. G4LNA

    G4LNA Member

    Has anyone else noticed this from HDMI ports? The reason I ask is that I get some strong noise on 14037KHz from the HDMI on our Sky plus box and TV which is a Sony Bravia. I have tried the usual, ferrite cores, in fact a whole string of type 43 mix clip-on beads along the whole length of the 1m cable, even some FT240-43 rings as close as possible to the output from the Sky box, also different cables in case the screen is different, but none have got rid of it including some very expensive cables.

    I do get the same on the shack desktop computer on 40m, but to a much lesser degree on 7018.5kHz.
    I have change the HDMI cable on the desktop computer to a DVI cable, but it is still the same, so I suspect it's coming directly from the Nvidia video card.

    I was wondering if using an Optical HDMI cable might improve the situation? But they are horrendously expensive and of course I'll be stumped if the interference is being directly radiated from the video board in the Sky box, although I can open it, which I have done before to replace the HDD, it's a bit of a faff because it isn't screwed together, it uses those nasty little tabs you've got to twist to undo the screen box, do that too many times and the tab breaks off :oops:

    I've also got a security camera system from Swann and that HDMI has no radiated noise at all, that I can hear anyway. And that has got a cheap and nasty £1.99 cable on that.

    It obviously isn't a huge problem because I can work around it, but the interference on 20m is quite strong and dirty, so it spreads out for a kHz either side of the centre frequency.

    This is a YouTube video of the noise.
  2. Ken G3SDW

    Ken G3SDW Moderator

    Two things you must make sure you use a well screened HDMI cable, they are not cheap but need to be used.

    Ferries need to be the correct grade not just any old ferrite and they need to be wound with as many turns as possible.

    These point are most essential.

    To find out what ferrite are needed then Google GM3SEK

    http://www.ifwtech.co.uk/g3sek/in-prac/index.htm#big31 and read his details on ferrite and RFI.

    73
    Ken
    G3SDW
    Last edited: Dec 8, 2018
  3. G4LNA

    G4LNA Member

    From my first post: "but none have got rid of it including some very expensive cables.


    From my first post: "whole string of type 43 mix clip-on beads" and later "FT240-43 rings" it's not possible to wind more than 7 turns on the FT240-43 ring because of the thickness of the HDMI cable. 43 is the correct mix.
  4. gm3sek

    gm3sek New Member

    7 turns on an FT240-43 has a significant impedance across HF (see G3TXQ at http://www.karinya.net/g3txq/chokes/ ). Likewise the 1m long string of beads will have a reasonably high common-mode impedance as well. If there was common-mode current on the HDMI cable, then either one of these chokes should have made some noticeable difference.

    The fact that reasonably effective chokes are not making any difference is simply proof that the interference is not due to common-mode current on the HDMI cable! It must be getting out by some other route.

    One possibility is that the cable is working exactly as it should, simply delivering the HDMI signal to the TV, and then the interfering signal is coming out on one of the other TV leads. You might try choking some of those instead.

    73 from Ian GM3SEK
  5. Ken G3SDW

    Ken G3SDW Moderator

    Thanks for your input Ian.
  6. G4LNA

    G4LNA Member

    Thanks Ian, I know the work Steve has done on ferrites and I use his site a lot when I'm building Baluns and chokes.

    I think I have come to the same conclusion as you, it isn't the cable, I have destroyed one of my expensive HDMI cables just to see what the screening is like, and it looks pretty good. I have tried the TV by disconnecting all the external cables apart from the HDMI and put a FT240-43 on the mains lead, that didn't cure it, next I'll take a closer look at the Sky box, the noise might be getting up the feeders to the dish which is located on the same mast as my HF doublet, about 20ft below it. Of course disconnecting the satellite dish the Sky box is going to tell me there's loss of signal, but there might be sufficient video content to hear if the noise is there or not, I'll have to work in conjunction with the house manager to do that (the wife). If it does cure it I'll try choking the satellite feeders with an FT240-43 ring, I've got lots of them.
  7. gm3sek

    gm3sek New Member

    Good luck, Paul. You're obviously thinking logically about the problem, which is more than half the battle.

    Even though you have lots of toroids, the large snap-on bead (http://www.ifwtech.co.uk/g3sek/in-prac/index.htm#big31) is still very useful as a diagnostic tool - simply because it snaps on quickly so you can immediately tell if it's going to have any effect, without cutting cables or removing plugs. If you get a positive result with a few turns through the large bead, then you can think about optimizing the choke with maybe a different core and number of turns.

    73 from Ian GM3SEK
  8. G4LNA

    G4LNA Member

    It's the television! I took the laptop into where the television is and plugged the laptop in using the an HDMI cable and the noise is still there, so the laptop in it's internal battery and the television without anything else connected and the noise is just as it was before.

    It must be the internal wiring or circuitry within the TV itself that is radiating, the TV on it's own internal tuner looking at terrestrial is fine, as soon as the HDMI cable is plugged in the noise appears. I don't really fancy taking the back off a 2 year old telly to go poking around inside unless I have to.
  9. Ken G3SDW

    Ken G3SDW Moderator

    Gone are the days that you can, as you say, poke around inside a two year old Sony TV.

    I am sure that it being a Sony it must still have warranty so exercise it, i will guarantee that with 55 years experience of TV`s modern and old you will never find the problem, they are not made to day to repair on the living room carpet.
  10. G4LNA

    G4LNA Member

    Latest update, with all my messing around I have found using HDMI port 4 has reduced the noise to a level I can just about hear it, so that is about 18db less than what it was with port 1. I found all the ports gave noise of some degree, port 4 was the least noisy. I haven't really got an answer to that apart from a guess at the way the ports are connected internally.

    I'll leave it at that, it's at a level I can live with.
  11. Ken G3SDW

    Ken G3SDW Moderator

    Well thats a result Paul, Sony are the least likely to cause any problem at all, so let sleeping dogs lye.
  12. G4LNA

    G4LNA Member

    I agree Ken, at least the Memsahib is happy that I'm not going to be messing with her baby, I hardly watch the blinkin' thing anyway.
  13. Ken G3SDW

    Ken G3SDW Moderator

    Thats the best decision you have made this year, she should always be obeyed lol

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