request for background noise information

Good morning.
... I would need information on how to eliminate a reception problem, if possible. (photo 1)
I have a KIWI receiving station connected to an MFJ-1886X antenna - both devices are powered by separate linear devices with low noise power [no switch] transformers.
All connected directly to the router with NETGEAR ethernet cable
I am not in the vicinity of power plants or mechanical workshops or laboratories of any kind, I have no electric motors nearby and by disconnecting the power supply from the antenna I have the following result (photo 2).
Are there any possibilities for not having this kind of ailments?

I attach the link to my receiver.

Thank you for any kind of help, awaiting best regards



  • Hi Fabrys,

    I think I see emissions of at least two switching mode power supplies in the spectrum, plus a bit of PLC noise.
    Can you elaborate the position of the antenna? It should be placed as far as possible from any power lines and electric devices.
    You can try to turn the loop, to locate or suppress the noise. Magnetic loop antennas have a distinct null in the radiation pattern, which is perpendicular to the circular surface.
    A noise source might also be the router/switches power supply. I had a netgear branded power supply that spread its noise via the ethernet wiring.

  • Thanks Stefan for the communication .....
    in the meantime I inform you that Kiwi, Antenna and Netgear are all with non-switch power supplies at Netgear I gave an Ifi IPower with noise equal to 1microVolt.
    I tried to connect the KIWI directly to the Router, but there were no improvements ...
    Tomorrow morning, before turning everything on, I remove all unnecessary transformers and PCs near the KIWI from the mains and try to see with a connection on the IPhone if there are still background noises.

  • To me it looks like pickup at the antenna or feedline. When I use switchers for the Kiwi (or close to it's supply) there is normally visible noise at the switcher base frequency.
    When I visited your SDR (yesterday) it looked to be all high up with remarkably little down at the lower end.

    The (UK) powerline kit I've seen normally has some defined guard bands I couldn't spot those in the short time I looked.
    Although your noise is also in the realm of VDSL frequencies again there are not the clean edges I can see here (most noticeably 80m band). So I do agree with Stefan there is switching noise I can't personally identify the PLC side. if that is PLC then I'll have to commit it to memory as it falls between types I see here.

    What I do when facing a new noise is zoom in to a dead part of HF then use the signal meter extension to record over a longer period.
    I look for clues, E.G. does the noise change at "advert breaks" (Plasma TV were obvious that way) or take one mode like a "loaded charger" until a neighbour goes out taking their laptop and mobile with them?
    Another common method is of course listen to the noise, get a feel for it then take a small AM radio around the house listening for that signature.
    I have a (wired telephone) signal tracer probe with a speaker, that is also surprisingly useful for switcher noise tracing.

    73 Stu
  • hi Stu

    I tried to disconnect a bit of all the electrical power I have at home but without any improvements.
    Obviously if it were to depend on elements I use to receive the
    Unpowered KIWIs would be of no use.

    I think the problem is outside my home and precisely
    in the series of repeater bridges in the photo ...


  • edited August 2020
    In that case do what Stefan already suggested and use the null of the loop to narrow it down.
    The sensitivity can be visualised as a doughnut (donut) arrange the antenna so that when looking at those masts, you are looking through the hole.
    In reality It is more likely to be something closer, in a neighbouring house, so use the null to find the direction(s).

    If there is great deal of RF power in the VHF/UHF and above range you may be able to reduce the issue by putting the loop in the (RF) shadow of the building. Mag loops can work surprisingly well just a few feet off the ground and if the pickup is a mixture of lots of high/super high frequencies that may help. Also ferrite, run the feed a good few turns through some FT-240 type 31 (or 43) loops. If you have enough feed you could make air loops first while watching the waterfall, we are looking for anything that changes the noise for better or worse as that should show the way it is getting in. The feed, if possible have that shielded from those masts and reduce any vertical runs.

    Power leads, get some 11mm or 13mm "clip on" ferrites and put as many turns as will fit through those on ANY leads going to the Kiwi or antenna, yes even from linear supplies. Whatever you do have two Kiwi browser sessions open and finely tune the waterfall. One session have the waterfall really slow (for example on a desktop computer) the other session on your phone watching changes with the waterfall at slightly slower than normal, make a change and give it a minute or two before making another, that way you should get feel for the change and be able to review the result on the desktop later.

  • @fabrys
    It looks now much better than the last time I've visited your kiwisdr.
    I don't think the distant transmitters have anything to do with your noise situation. I still think that it is coupled from a power line near the antenna. Do you have any overhead power lines nearby?

    If you rotate the antenna, and the noise pattern doesn't change, then the noise is coming through the cable. But I doubt that, those loops are generally good decoupled.

    @Powernumpty here are the PLC signals that I've spotted in his SDR, they have notches for amateur radio and CB:
  • .... this is the area ... the only overhead electricity lines present are a 3 kV dc contact line on the Italian railway network FS / RFI. Red line in the photo
  • @HB9TMC Ok got it, I didn't spot that in the short time I was looking, that is what I see here from Sky Q junk.

    On talking to Fabrys I'm coming to the conclusion his 5V may not be a linear, it was supplied with encapsulated ferrites in the DC lead...
    That noise very clear, almost too clear to have come through other devices.
  • Good morning....

    for those interested in the subject, today I installed number 4 FT-240/43 toroids, two at the beginning and at the end of the antenna cable, before its amplification circuit and two more on each of the antenna power supplies and of KIWI, it seems that there have been improvements, taking into account that there is a vast depression with thunderstorms.

  • try... antenna+ferrite-----------------------ferrite+(coax junction with good ground)+ferrite-------------------------Ferrite+radio
  • Thanks, but in the end I opted for a QRM eliminator from WIMO and a wire auxiliary antenna .... even if the background noise is only partially excluded ... I tried to remove the MFJ and mount only the wire, but the reception it is almost impossible in the whole HF band.
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