Power line noise ?

Hi everyone, I have this noise that is quite annoying and when I go outside with my portable radio it's very loud when I stand under the 10Kv line going over my garden, I followed this last night on foot through a field in the dark for some distance and it's the same doesn't increase or decrease.

Tonight I went out in the car with the radio and passed a house with an incredibly noisy LED flood light.

The noise is audiable from around dark and I don't know when it stops because I'd most likely be in bed so I'm wondering if this LED noise can travel from this light through the Persons house wiring and through the transofrmer on the pole and back out on this same 10 Kv line ? this house is around 1.5-2 miles away, surely the LED light can't emit noise this far ?

Listen to it on my Kiwi here http://emeraldsdr.proxy.kiwisdr.com:8073/ and tell me if this sounds like power line noise , QTH is Ireland, so power frequency is 50 Hz. Tune to 6920 Khz and you will hear the Noise I'm talking about, it can be heard at different frequencies.

Sounds similar to the noise emitted from the LED floodlight 1.5-2 miles down the road but yet if I stand under the 10kv line it's really loud on the portable.

And why would it be only after dark ?



  • The family of lines in 6.5-7 MHz you suggest seem to me to be power line related, though this is true of many SMPS noise sources. When I detect in 10 kHz AM and analyze with Audacity I see astrong 50 Hz family/component

    This is as expected from an imperfectly filtered SMPS input. Furthermore, the spectral width of the lines is consistent with jitter/phase noise of a switcher's rate and it appears to have stronger even harmonic components, as is common from full-wave rectification.

    But as to the actual source and coupling mechanism - that's harder to say. There are so many uses for SMPS supplies these days, some of them for lighting related power that an after-dark correlation is not unlikely.

    To put things in perspective, while your noise floor is no doubt raised considerably by this, you are in pretty good company and a lot kiwiSDRs reveal similar and worse results. If you are using a well matched antenna, your noise is about 30 dB above kTB which isn't so dreadful at that frequency. OTOH, it may be higher than that if your system is not well matched to the radiation resistance. You could be seeing CM currents, current in the earth below or other coupling mechanisms. I suggest not first considering it to be inverse-square radiation. That is actually much rarer, in my experience.

    Glenn n6gn

  • edited January 2021

    Hi Glenn,

    Many thanks for your detailed reply, I was suspicious it could be SMP related, sometimes it's worse around 9 Mhz but one thing I have no doubt about is that the 10 Kv line is radiating this noise this is why I'm uncertain as to the source and I'd find it incredible if this LED flood light 1.5-2 miles down the road could be sending this noise through the house wiring into and through the transformer on the pole that supplies their house and out along the 10 Kv line, is this possible ? I do know that the LED light is emitting massive RFI, I stopped at the house and it drove the radio nuts but that was at around 10 Mhz.

    It is effecting weak signals on 40m and other bands. I really want to be sure it's power company related or not before I contact them again........ I had/have issues where 14 Mhz and above is basically wiped out due to noise from a pole in the Sheep field beside me and sometimes you could hear it like it was being effected by wind so one day while it was calm and I heard no noise I went to the field and shook some poles and they were all silent except one, when I shook it it drove the portable radio mad exact same noise that I heard through the 7300 so I contacted the power company and one Lad called out many Months later and I shook the pole for him and sure enough the pole was quiet as a mouse and he said it's possible it's the hardware on the pole and he would pass it on to his supervisor and I heard nothing more, I first contacted them in 2017 but that seems to be more of an Issue during warmer weather.

    Last year I had similar issue and it's probably the same, but I was working night shift and I monitored this noise and around 2 am or 3am it stopped, just like that so It probably is SMP related and not the power company, it's just amazing to think that this LED light almost 2 miles away could be causing this 10 Kv line to radiate such noise, it could be some cheap junk they bought in China over the internet.

    The antenna I'm using on the kiwi I linked to is the Bonito Ma305 and I have one of their chokes and it made no difference. My other Kiwi has the Bonito Mega Dipol and it doesn't suffer from this noise as much at all but my EFHW does that I use with the 7300.

    Any time I pass this house in the dark this LED flood light is on, it's obviously on a timer, it wouldn't be so bad if it came on and went off again but one of the issues with LED lighting, at least here in Ireland is that so many People have them all of a sudden and so many People leave them on all night and never turn them off because they are so much cheaper to run and everywhere you look there's flood lighting everywhere now. I wouldn't mind only these lights are expensive to buy and People just don't get that you'd run a good O'l halogen for years before you recoup the cost of some of these lights I've seen at 60+ Euro's and more.

    I never thought I would have such issues when we moved to this location in the country.



  • The horizontal polarization of the dipole might be helping. Most QRM tends to be vertically polarized. Balanced antennas can be better over unbalanced too. You might try a horizontal, balanced antenna and see what happens (dipole, loop, etc.).

    I suppose you could also go talk to the person with the light, explain to them what you think is going on in the most polite way possible. Ask if they can turn it off temporarily so you can verify that is the cause. If it is, maybe you can offer to buy them better LED bulbs...if there is such a thing. I have Philips ones and I don't notice any issues.

    Good luck!

    Nick W1NJC

  • I'm listening to your SDR now but I don't hear it, probably because it's too late (0108 UTC). In fact you have a remarkably quiet QTH compared to mine (San Diego CA DM12ju). But your description sounds remarkably like one source of QRM I'm working on here: clearly power line related, very unstable lines from a switching power supply, present after dark until the middle of the night, worst on the 49m and 40m bands (receiving with a G5RV).

    The switching frequency appears around 20 kHz, i.e., the lines blanket the spectrum every 20 kHz. My hunch is a compact fluorescent bulb, as their switch mode ballasts produce 20 kHz AC where CFLs are most efficient.

    As for the noise coming down your power line, yes, this is exactly what I'd expect. Electronic noise below about mid HF is generally conducted out through the power line since the device itself is too small to be an efficient radiator.

    Have you offered to buy your neighbor a new, clean light bulb? That's what I plan to do once I find out who to offer it to.

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