Problem with interference at 50MHz

Discussion in 'EMC Matters' started by Martin - G4ENZ, Apr 25, 2017.

  1. Martin - G4ENZ

    Martin - G4ENZ New Member

    Please can anyone identify what this is from its pattern? It is sometimes absent for hours at a time but here is how it has looked this afternoon. The graph of signal strength over time was created from data produce by HDSDR averaging the receiver shown in the first image.

    HDSDR screenshot.jpg
    Reception graph.jpg


    73 Martin - G4ENZ
  2. Ken G3SDW

    Ken G3SDW Moderator

    With total respect Martin what is the point in trying to see what it is, knowing were it is coming from is more important.

    That will not locate it and eliminate it all,so the very first thing you must do is to turn off your mains supply and monitor the problem on a portable RX and then assuming that it is still there do a walk about to try to locate its position

    Then comes the hard bit and that is knocking on the door, tread lightly and never accuse.

    SDR`s are used quite a bit today and have their place in our hobby but to identify what is causing a problem such as your is virtually impossible.

    How long has this been going on, do you know if any of your neighbours have had anything new installed and the most important thing i would like to know is are you on good terms with both of your neighbours, they no doubt will hold the key to solving your problem.

    73

    Ken
    G3SDW
    EMC Help Desk
    RSGB
  3. Martin - G4ENZ

    Martin - G4ENZ New Member

    Hello Ken,

    Thank you for your reply. I thought one part of the puzzle was to be able to recognise the interference from how it looked. Certainly DF'ing and public relations are vital to any resolution but I had thought this might be a place where someone would say "I've seen that before". I was just interested to know, that's all. For all I know it might be VDSL.

    To answer your questions...

    No, it is not generated in my house.

    I have a 3 ele quad on 50MHz and the interference peaks well away from my nearest neighbours implying that it comes
    from some distance. Probably > 300m.

    This interference is new to this SpE season, i.e. it wasn't there last year BUT 6m has always had many sources of noise on all sorts of beam headings. It is just that this one has popped up in a direction that was previously relatively quiet.

    I will be trying to find the source but firstly, I wanted to know if there was a pattern to it. Knowing this would assist in choosing an optimum time to walk the estate. Remember I said that it goes away for periods.

    73 Martin
  4. Ken G3SDW

    Ken G3SDW Moderator

    I fully understand what you have said but there is no point in assuming what it is and just not locating were it is coming from.

    Sadly today there are so many different reasons for what and where RFI is located.

    I will leave it to you to try to make sense of what and were it is coming from and maybe but if you come up with the answere then could you update the forum to help others with future problems.
    73
    Ken
    G3SDW
  5. Peter Torry

    Peter Torry New Member



    Martin,

    As there has been an early sporadic E opening have you considered the possibilty of it being from Easter Europeas television transmitters. The signal is every 16kHz or so which is indicative of a television time base and they sound like a rather rough distorted signal either on SSB or AM. Check you beam heading where it peaks up and if it coinsides with other signals on the band that may give you a clew.

    73
    Peter
    G3SMT
  6. M0JAV

    M0JAV Moderator

    It looks like a real signal rather than RFI. It may well be a long way from you. The spectral lines are at ~105Hz you can probably give us an accurate figure the peaks about 15.6kHz so I agree it could be a television timebase. A walk around as Ken suggested will help if it is a local source but if it is further away you would need to find someone else can see it in order to triangulate.
    There is an excellent site for waterfalls and audio of different types of signal http://www.sigidwiki.com/wiki/Signal_Identification_Guide
    In this case I can't find anything on that frequency.
    Would be interested to know what you find
    John M0JAV

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