Help identifying HF interference

Discussion in 'EMC Matters' started by Ste, Feb 12, 2016.

  1. Ste

    Ste New Member

    Hi

    Can anyone help identify what could be causing the interference shown on the waterfall screenshot below? It has only started in the last week or so but it doesn't seem to be on all the time.

    However it is very disruptive and causes my noise level to jump up and down right across the HF spectrum.

    Stephen

    Attached Files:

  2. G3NYK

    G3NYK New Member

    It would be more useful if you could switch off the station identifiers on the spectrum and indicate the time interval on the waterfall.

    The comb on the spectrum display has an approximately 50kHz "tooth spacing" This indicates to me that it is most likely to be a switch mode power supply or charger of some kind. Next check to make is does it interfere with Radio 4 longwave (198kHz)?? and can you record for a number of days the times of interference occuring. This helps greatly to identify the source. Make sure it is not a new gadget in your ownhousehold, new phone charger, or other cordless equipment.

    Next an small MW portable radio with a ferrite rod aerial is a useful device for DFing the location of the source. Details of your aerial, and its location would help give a feeling for the geography. This includes the proximity of neighbours.

    Alan
    G3NYK
    Ste likes this.
  3. Ste

    Ste New Member

    Hi Alan,

    Thanks for that. I will keep monitoring it tonight and in the days to come. I don't believe it comes from my own house as I have turned off my power and the interference is still there. I have attached a screenshot of the interference without the station names and with a timestamp on it as well as the LW band.

    http://i.imgur.com/nYl7Kvk.jpg
    http://imgur.com/YxCbiHg

    My location is Southport, Merseyside and I am using G5RV Jr. antenna.

    Stephen
  4. G3NYK

    G3NYK New Member

    Ok Stephen you have made a good start. It is easy to be caught out. A frend of mine had a problem and found his wife had used a spare mains socket in the room he uses to charge up her new phone !!

    Radio 4 seems well clear of the noise, which I would expected to have been stronger in the LF area than your display shows. If you have not done it yet do look at the EMC leaflets which give give information on the type of interference and ways of tracing the source.

    Alan
    G3NYK
  5. G3NYK

    G3NYK New Member

    Another thought, I was neglecting the waterfall. Is it the yellow bursts of noise that are giving the trouble?? If so this might be broadband (ADSL, it doesnt seem wide enough for VDSL) Have you or your neighbours changed supplier or contract recently?? The gap at 3.2MHz looks significant. Again there is a new leaflet that helps to identify interference from broadband. Most problems occur when the the telehone line enters the property via a distribution pole and overgead wire.
    On the main RSGB site go to Technical/EMC and click the publications and leaflets (on the right). The new leaflet No 15 may be helpful.

    Sorry for the false start (though I guess there is some SMPS noise there) The spectum sample may be between the bursts shown on the waterfall. Is anyone using the net at the times of problem. Are your neighbours in? etc

    Alan
    G3NYK
  6. Ste

    Ste New Member

    Hi,

    Yes I have VDSL and have done for some time, however my own router off or on doesn't make any difference to the noise. On last night evidence it also seemed to be happening all night. The yellow burst's are giving trouble but not so much them around 2Mhz but the fact that there are pulses radiating across the bands from that point.

    By walking around with a portable radio I think it is definitely coming from nextdoor, just across the room from where my radio is. The video doesn't actually show the difference in noise to be as much as it is but the noise on the radio gets much louder when I move it from my office (at the start) to next to the adjoining wall - .

    I suppose I will have to try and ask them about it!

    Stephen
  7. Ste

    Ste New Member

    Getting even worse tonight now over 1.8 - 3.9Mhz, 6.2-8.5Khz (screenshot attached), 10Mhz - 12Mhz.

    Attached Files:

  8. Ste

    Ste New Member

  9. Ken G3SDW

    Ken G3SDW Moderator

    Until you ask Stephen you will never know, bite the bullet and dont accuse, just ask them if they could help you locate were it is coming from.

    You need Cooperation from whoever it is and if the turn the other way then you are lost.

    This is just my basic rule of thumb.

    73

    Ken

    G3SDW
    Last edited: Apr 25, 2016
  10. G3NYK

    G3NYK New Member

    Hi Again Stephen as Ken says you will probably have to ask. One strategy I have used with a friendly neighbour when you ask if he has anything newly installed........
    Say you are concerned because loose connections or broken wires often arc and that produces radio "noise", but it often indicates a hidden problem which if not rectified can lead to a fire. I have experience of this effect in various guises. Fortunately all bar one solved successfully, but that electrical fault one led to the complete destruction of a nearby property, and severe damage to the attached property.

    This gives some incentive for the neighbour to cooperate initially even if its not a "loose wire", it is worth his while attempting to find it.

    That waterfall is more informative, but a bit worrying. The bursts are randomly spaced and at roughly 2 seconds apart. It is also interesting that this is higher in the spectrum than your original picture. It does not look to me as though it is any form of data transmission (ie PLT) but could well indicate a failing applience.

    Good Luck
    Alan
    G3NYK
  11. Ken G3SDW

    Ken G3SDW Moderator

    Alan, i think frightening to socks off of a neighbor is far from being a good idea, this is last thing that should be coming from the society.

    73

    Ken
    G3SDW

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