RFI mystery... Any ideas as to what's generating so much energy? - Page 1
Forum section: electronics / rf-microwave

author: Co6aka
author_rank: Unknown
timestamp: November 20, 2020, 01:57:11 am
content: I've narrowed down the source to a several-block area about a half mile from me, but nothing is obvious. I found a deep null with my rooftop RX loop (on a rotor) and that area is exactly to the broadside of the loop. Unfortunately when it goes wild like in this video I'm usually otherwise occupied and can't go foxhunting.https://n2cbu.com/RFI/VID_20201109_110348.mp4It has a few "modes" of operation: full-blown meltdown like in this video; continuous arc-like crackles similar to what's heard a few brief times in this video; occasional arc-like crackles as if an arc were trying to draw; and sometimes just a boiling white noise like hash all across the spectrum. In the HF spectrum it seems to peak in 2MHz increments: 2-3MHz, 4-5Mhz, 6-7MHz, 8-9MHz, etc. It's audible up through 54Mhz where beyond it's covered by HDTV signals. There's also a huge 100kHz wide band of crud centered at about 500kHz, in addition to the VLF-LF crud you see and hear in the video.The one time I was able to drive around when it was in meltdown mode, the AM-BCB radio in my car was obliterated over a particular several block area, and my portable spectrum analyzer displayed a -40dBm peak at 500kHz with just a 20-inch whip antenna on it.It's a LOT of energy being transmitted, so I presume it's mains-related. I'm hoping that someone might recognize/realize what's making all this RF-crud.

author: 0culus
author_rank: Super Contributor
timestamp: November 20, 2020, 04:33:14 am
content: Don't forget to look closer to home too...it might be a failing SMPS in an appliance like a newer refrigerator.

author: radiolistener
author_rank: Super Contributor
timestamp: November 20, 2020, 07:49:52 am
content: it looks like powerful PWM regulator or SMPS with no filters or broken filters

author: coppercone2
author_rank: Super Contributor
timestamp: November 20, 2020, 02:25:50 pm
content: the front panel for refrigerators where you pick the settings does alot, so does the stove. My Phillips LED light bulbs block the radio alarm clock that is sitting on the table next to them.

author: Co6aka
author_rank: Unknown
timestamp: November 20, 2020, 03:11:55 pm
content: It's nothing close to me: -60dBm to -70dBm in my neighborhood, and -40dBm to -50dBm in the suspect area.After probing around at home, before looking elsewhere, just to be sure, with my receiver and loop on battery, I shut off the main breaker and nothing changed. And yes, I've unpowered the loop and the RF crud is almost as strong on my passive antennas. I'd previously checked my UPSs and they were powered-off. The RF crud is relatively constant around my neighborhood, but it increases significantly as I go towards the suspect area, which is about a half mile away. (My fridge is about ten feet away.)That it sounds like a motor had me looking for a large generator, but I've neither seen nor heard any in the suspect area, which is mostly residential. The RF crud is probably being conducted on and radiated by the mains wires, which explains the wide area of strongest signal.Also, it's something outside because the wind influences it. Last Sunday evening a strong front passed with brutal straight line winds, and the crud instantly stopped as the winds hit. It then went through its modes and settled on the occasional arc-like one. Midweek, it was doing its continuous arc-like thing, which corresponds with the greatest noise on VLF/LF. (When it goes into Fukushima-mode the VLF/LF noise is reduced by several dB.)I want to learn what makes such an effective broadband RF jammer!And then of course shut it down.

author: David Hess
author_rank: Super Contributor
timestamp: November 20, 2020, 06:35:15 pm
content: The wind suggests discharge through a damaged insulator on a high voltage power line.

author: radiolistener
author_rank: Super Contributor
timestamp: November 20, 2020, 07:45:31 pm
content: Quote from: Co6aka on November 20, 2020, 03:11:55 pmdo you have High Voltage Line within several miles around your home? Common problem with High Voltage lines is a damaged insulator. It leads to sparks and affects short wave up to 10-15 MHz with a strong interference.If you have high voltage line near your home, you can get pocket AM receiver and walk several miles along the line. You will hear where broken insulator is by high noise amplitude near it.Usually broken insulator has maximum interference in dry weather and disappears after the rain. Or vice versa.If you found broken insulator, call the service which owns that high voltage line and report them about the problem and where it happens, they should fix it within several days.

author: Co6aka
author_rank: Unknown
timestamp: November 20, 2020, 09:46:51 pm
content: Primary distribution lines here are 4kV, 13kV, 27kV and 33kV. The suspected area is mostly residential, so most likely 4kV and maybe 13kV on some main streets. The RF crud is within a 10dBm range throughout the suspect area; no more-significant peaks than that.In the past, the utility was reasonably responsive, but when I called recently they essentially told me to contact the FCC if I'm experiencing RFI. I used to have a fax number directly to the enforcement desk of the local field office, but it no longer works. (They required a written signed letter to open an investigation.)Arcs are much more easily found with ultrasonic gear, so I guess I'll have to look into building something.Anyway, if it's an arc then Marconi would be proud of this "transmitter."The more periodic "sputtering" waveform when it's in Fukushima-mode sounds and looks more like vibrating plates in a transformer. And, there's another possible clue...Years ago I made a EMI probe using a Test-Um TT100 telephone tone tracer on which I replaced the dummy plastic tip with a 6-inch "rubber duckie" whip antenna, plus a couple of circuit mods. It's super-sensitive to electric fields but not to magnetic or electromagnetic fields. In the suspect area it detects only "the usual amount" of 60/120 crud, while at the same time a AM-BCB radio is obliterated. So, I'm thinking it could very well be a transformer inside a steel enclosure. Probably I need a magnetic probe for my portable analyzer.

author: coppercone2
author_rank: Super Contributor
timestamp: November 20, 2020, 10:04:55 pm
content: Hmm, I have a few of those tracers, I think one had exchangeable tips.

author: Co6aka
author_rank: Unknown
timestamp: November 21, 2020, 12:31:30 am
content: The tips are for sifting through wire bundles. Non-conductive; at least I read an open circuit measuring in the 10G-Ohm range. The duckie element I installed is electrically connected to the PCB/circuit. It's been a very handy tool for a wide variety of tasks.

author: Syntax Error
author_rank: Frequent Contributor
timestamp: November 21, 2020, 12:56:58 am
content: It's not some kind of ethernet over mains or other smart meter wide area networking (SMWAN) that your power company is experimenting with? Early domestic ethernet over mains devices were notorious for hammering HF bands, at least for the ham next door.https://www.rtl-sdr.com/showing-the-hf-interference-problem-from-ethernet-over-powerline-devices/

author: Co6aka
author_rank: Unknown
timestamp: November 21, 2020, 02:01:22 pm
content: Totally different, and it's not "steady" like BPL and etc.Last night it was mostly quiet, but this morning it's doing its intermittent attempted-arc thing. The VLF/LF noise is almost always steady. The RF crud is all on the same vector from my location, which precisely points toward "area zero."I wish whatever it is would hurry up and explode in a glory of sparks and flames.

author: madires
author_rank: Super Contributor
timestamp: November 21, 2020, 02:43:52 pm
content: Plasma TVs, PV inverters, cheap/bad SMPSUs, ...

author: David Hess
author_rank: Super Contributor
timestamp: November 21, 2020, 11:01:44 pm
content: Quote from: Co6aka on November 20, 2020, 09:46:51 pmAfter you find the broken insulator, shoot it when nobody is looking.

author: A.Z.
author_rank: Super Contributor
timestamp: November 22, 2020, 08:00:12 am
content: can't you perform some triangulation to progressively restrict the area and locate the source ? you may use a laptop to draw lines on a map and a loop antenna (and receiver) to find the source direction relative to your position; you may also need some adjustable attenuator to pinpoint the source when you'll get near, but I think it could be possibleEDITcheck this paperhttp://www.arrl.org/files/file/RFI/Thompson%2520Noise.pdf

author: dropkick
author_rank: Contributor
timestamp: November 23, 2020, 05:12:43 am
content: Have you tried looking around up in VHF as well? Might be a quick job for that specturm analyzer if it's overloaded on HF. I seem to recall a couple of videos where the power co was using ~2m and a yagi to pinpoint a pole. You can take a hammer to the pole and change the noise as well to confirm.Or grab the FLIR and do some nighttime pole recon! If you find a problem and report it as a possible broken insulator the power company will listen; it's not a mystery tinfoil RFI problem to them at that point.

author: srb1954
author_rank: Super Contributor
timestamp: November 24, 2020, 07:48:28 am
content: Quote from: dropkick on November 23, 2020, 05:12:43 amThe hammer method is very effective at identifying poles with bad insulators. Just don't do it in an urban area as you might get the police turning up and tasering you.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 28, 2020, 11:04:54 pm
content: Have you listened to the CB bands when this occurs?Some of these guys use huge power amps and even 3 phase stuff and over 20 KW output.Their amps are not noted for being "clean"And besides that, it is fashionable to blame CB radio....I don't like the idea of hitting a pole with a hammer. The transformer may come down on your head.

author: james_s
author_rank: Super Contributor
timestamp: November 28, 2020, 11:21:13 pm
content: If hitting the pole with a hammer causes anything to fall off then it was in a seriously bad state to begin with. They should tolerate high winds and substantial impacts without any damage.

author: coppercone2
author_rank: Super Contributor
timestamp: November 30, 2020, 02:39:15 am
content: i suggest using a rubber mallet because it looks like you might have an idea of what you are doing, if you go out and start beating pole with a carpenter hammer you might cause suspicion. It also wont leave a mark 'vandalizing' the pole.Maybe you are just looking for termites or something

author: CJay
author_rank: Super Contributor
timestamp: November 30, 2020, 01:46:57 pm
content: Quote from: Wallace Gasiewicz on November 28, 2020, 11:04:54 pmThey run 'Superbowl' sometimes, around CH13 IIRC and even here in the UK some of them end stop the meter with five or six channels either side being utterly unusable, why nobody is hunting them down in the US heaven alone knows, they must be *killing* huge chunks of HF for you guys.

author: james_s
author_rank: Super Contributor
timestamp: November 30, 2020, 08:48:22 pm
content: Is CB still a thing even? I know some 4x4 guys use them out in the woods still, but I have the CB frequencies in one of my scanners and it's been very rare that I've heard anything at all, just the occasional trucker passing through. I remember back in the 80s and 90s CB was full of activity and that was well past the heyday in the mid 70s.It has struck me as about time for it to make a comeback with the hipster crowd, what's old becomes new again but so far I haven't heard of that happening.

author: CJay
author_rank: Super Contributor
timestamp: December 01, 2020, 07:33:03 am
content: Quote from: james_s on November 30, 2020, 08:48:22 pmIn the UK it's a bunch of old blokes trying to relive their heydays, a few hipsters, some younger geeks and yeah, there's a few 'incognito' hams using it, it's alive but only barely.Given the supposed appearence of the new sunspot cycle I suspect it might make a bit of a comeback

author: Psi
author_rank: Super Contributor
timestamp: December 01, 2020, 08:25:55 am
content: Maybe someone near you has a big tesla coilbut being serious, it does sound like what I would expect mains HV arcing to sound like.

author: tautech
author_rank: Super Contributor
timestamp: December 01, 2020, 08:34:44 am
content: Quote from: srb1954 on November 24, 2020, 07:48:28 amWanna hit something hard, barely mark it and shake it to its core then a maul is the thing to use.My 2 are in a bit better condition than this one and I use them lots more than a sledge hammer.

author: Emo
author_rank: Regular Contributor
timestamp: December 01, 2020, 09:11:37 am
content: Hi,Any overhead DSL lines running through your neighbourhood. It will effectively transmit over a very broad frequency up till 17-31 Mhz. Due to the lines running all over it is difficult to trace the origin. To comms receivers at first it looks like a lot of noise.Eric