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Author Topic: Power lines only occasionally cause RFI?? Would it be possible?  (Read 11740 times)
KD0PBO
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Posts: 67




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« on: February 24, 2014, 06:20:21 PM »

So, I'm dealing with an RFI issue from somewhere. It sounds like the classic 60hz hum of a bad power line connection but only causes interference occasionally. We have had pretty wild weather swings here in Saint Louis so could that cause the lines to only occasionally cause problems. Also, it only seems to happen/be noticeable at night. I do have above ground power lines that run along the back fence of the yard with a pole located at the corner of the yard. The pole also holds a transformer that could be the culprit but when I strung up my dipole, I made sure that the transformer was off the end in the null. To restate it, the noise only affects my receive occasionally, and most often at night with a solid S9+ signal on HF and VHF. Is worse on AM but is noticeable on USB, LSB, and even on my FM 2m rig  Huh Huh.

Could this be something other than power lines? I've heard some people say that ATT Uverse dvr's can cause problems, which we do have in our neighborhood. Is there any truth to that? I've ruled out my main power supply by running things on battery power and a back up power supply and the noise is still there. Shut down florescent lights in the house, computers, TV's, stereos, etc..

I've walked the yard and house with a portable AM radio and can't really find a hotspot, so that has been tried. I'm mainly just looking for ideas of other things this might be...(Of course I guess the neighbors could always be the culprit  Undecided )

Thanks guys!
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KI6LZ
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« Reply #1 on: February 24, 2014, 08:43:31 PM »

First you're lucky you can hear the noise on VHF. Some type of directional 3 element beam for 2 meters should help confirm the location of the noise.  The AM radio on broadcast band is only helpful in getting closer to one pole of many. First rule in finding power line noise is start at a lower frequency then move up as location gets isolated, I use a Grundig that goes up to 30 Mhz. Even though the dipole is off end, it still picks up significant RF from reflections or from above and below. I'm dealing with a noise problem that only goes up about 50 Mhz, not easy to build a 3 element beam and haul it around in the car. Hi
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AA4PB
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« Reply #2 on: February 25, 2014, 05:41:42 AM »

Power line noise can be intermittent and it can be affected by the weather. It's usually caused by arcing connections on insulators on the pole(s). I notice that the noise is worst in very light sprinkling rain. Heavy rain often causes it to stop.
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WX7G
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« Reply #3 on: February 25, 2014, 05:57:32 AM »

The first troubleshooting step is to run the rig on battery power and shut off all AC power to the house, not just selected items.

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K5LXP
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« Reply #4 on: February 25, 2014, 05:59:07 AM »

Hearing it on HF through VHF means it's terribly strong or very close.  You should have no problem finding the source.

Twice in my neighborhood I've tracked "power line" noise down to defective streetlights.


Mark K5LXP
Albuquerque, NM
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W2JUV
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« Reply #5 on: February 25, 2014, 09:49:31 AM »

K5LXP..you are sooo right about streetlighting causing RFI.  A common occurrence is a lamp that is nearing the end of its service life and cannot maintain a continuous arc. So it goes thru many on/off cycles, and each time it restarts, significant RFI is produced.
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KI6LZ
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« Reply #6 on: February 25, 2014, 10:13:43 AM »

Street lights are very easily identifiable here, they cycle with about a 30 second repetition rate. I find about 4 per year around here and Edison usually repairs them within 4 days.

I use S Meter lite to capture my s meter reading for over several days. I have it set to sample once every 10 seconds. That's one of the ways to get an idea about the problem. It helps answer questions as to when the noise starts and goes away. If it always starts and stops at the same time that would indicate some type of timer device. If it starts and stops at dawn and dusk that would indicate either a photoelectric timed device or humidity. I think you see the advantage of knowing its periodicity.

Also the power line noise is mostly 120 Hz, twice the 60 Hz since there are 2 voltage peaks during  1 cycle of 60 Hz, one on the positive peak and one on the negative peak.

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KD0PBO
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« Reply #7 on: February 25, 2014, 05:19:16 PM »

Thanks for the replies guys.

As I type this, the interference is not there. The weather is cold and lite snow/sleeting. I will start righting this all down to figure out if there is a pattern. I'll also have to try the battery power trick again and shut the whole house down to see what happens.

Sounds like my weekend project is to make a 3 or 4 element beam for my 2m handheld and wait for the noise to reappear so I can track it down. It is about an S3 on 2m but is loud enough to notice.

STREET LIGHTS!! Gosh I didn't even have those cross my mind. We have a lot of them here in my neighborhood with one smack in front of my house, across the street. Could be a good possibility since this interference only seems to occur after dusk. Will have to check into that more.


Thanks again guys

73
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N3HEE
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« Reply #8 on: February 26, 2014, 10:24:33 AM »

If its that strong on 2m then its very close to you.  Possibly right outside your door!  Here is a neat little 3 element yagi I built to locate my noise problem.  http://www.youtube.com/watch?v=fLOvSLXDudU
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WE0Z
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« Reply #9 on: March 03, 2014, 06:04:32 AM »

This sounds like a porcelain insulator with a hairline fracture ussually caused by a lightning strike. The hairline fracture creates a gap that arcs usually in light rain or high humidity and subside when it gets saturated with water and stops these are usually intermittent and hard to locate but can be done when you isolate it to about the vicinity it is in notify your power company and be sure to let them know you are a licensed ham radio operator this usually results in a response as they know ham know that they are required to clean it up and can be find for not acting. Be cordial and by no means don't be an ass about it and be patient as you are not the only customer!
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KD0PBO
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« Reply #10 on: March 05, 2014, 11:15:54 AM »

Thanks for the additional responses. I'm pretty sure it was one of our streetlights on the verge of failing. I noticed the other night that one of the lights was burned out and has been out very night for the past week. Since then I haven't had any issues with the interference.

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K8YS
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« Reply #11 on: March 11, 2014, 03:55:07 PM »

you are going to have to locate the source. A sledge hammer is a good tool. Carry a receiver, usually a portable AM radio, then walk up to the pole and give is a health smack. WARNING, the power company is not going to overly impressed with you, so do this when you can be... inconspicuous.
Listen on the radio to see if the noise changes.

Here is what happened to the hams in West Chester, OH.
We have WLW in the back yard, we used to have Voice of America, but when VOA went silent, so did the kitchen florescent light fixtures. Anyway, WLW is on 700KHz, a flame thrower, Clear Channel, 50KW full time... running almost due south from WLW crossing the township is a street called Snider Rd.
Local hams started having interference that went from 160 meters to at least 2 meters and this interference went on 24/7. Oddly enough, and thanks to the ham wizards in the area, some serious who's who in SBE's member directory, tracked it down to  Duke Energy power poles, all along Snider Rd. The aerial ground wire, that sat in the saddle at the top of the pole, over the years had formed oxide, CRYSTALS, and EVERY ground lug was radiating.

It took the FCC to intervene to force Duke energy to fix the problem, but for several years, HF was not usable south of Tylersville Rd near WLW.

Moral of my story, expect the unexpected and examine every detail.
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N3AB
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« Reply #12 on: March 12, 2014, 05:12:20 AM »

you are going to have to locate the source. A sledge hammer is a good tool. Carry a receiver, usually a portable AM radio, then walk up to the pole and give is a health smack. WARNING, the power company is not going to overly impressed with you, so do this when you can be... inconspicuous.
Listen on the radio to see if the noise changes.

Here is what happened to the hams in West Chester, OH.
We have WLW in the back yard, we used to have Voice of America, but when VOA went silent, so did the kitchen florescent light fixtures. Anyway, WLW is on 700KHz, a flame thrower, Clear Channel, 50KW full time... running almost due south from WLW crossing the township is a street called Snider Rd.
Local hams started having interference that went from 160 meters to at least 2 meters and this interference went on 24/7. Oddly enough, and thanks to the ham wizards in the area, some serious who's who in SBE's member directory, tracked it down to  Duke Energy power poles, all along Snider Rd. The aerial ground wire, that sat in the saddle at the top of the pole, over the years had formed oxide, CRYSTALS, and EVERY ground lug was radiating.

It took the FCC to intervene to force Duke energy to fix the problem, but for several years, HF was not usable south of Tylersville Rd near WLW.

Moral of my story, expect the unexpected and examine every detail.

Bad advice!  Many power companies (the one I work for included) will prosecute you for vandalizing their property.  The pole does not belong to you, so you have no right to start "smacking" it with a hammer.  Hitting a suspect pole may also cause a power outage if something is ready to break.  There is also a distinct danger of a cracked transformer switch, failing lightning arrestor, etc shattering with pieces falling on you or nearby vehicles.

Don't do it, please!
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W0BTU
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« Reply #13 on: March 12, 2014, 06:45:53 AM »

Bad advice!  Many power companies (the one I work for included) will prosecute you for vandalizing their property.  The pole does not belong to you, so you have no right to start "smacking" it with a hammer.  Hitting a suspect pole may also cause a power outage if something is ready to break.  There is also a distinct danger of a cracked transformer switch, failing lightning arrestor, etc shattering with pieces falling on you or nearby vehicles.

Don't do it, please!

Well, I don't think that a little tap will hurt anything. I've used a hand sledge to stop arcing many times in the past, but I didn't hit it hard. If you tap on the right pole, it just takes a light tap to affect the noise on the portable radio in your other hand.

You can probably do more damage by yanking on a pole guy too hard. I've seen cows scratch themselves on pole guys, and the transformers and wires really danced! No harm was done, but I sure wouldn't try and duplicate what a big cow can do.
« Last Edit: March 12, 2014, 06:49:43 AM by W0BTU » Logged

KD0PBO
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« Reply #14 on: March 12, 2014, 10:47:31 AM »

Dont worry guys!! I'm not gonna go around and start smacking power poles around the neighborhood...

The problem was a street light bulb that was on its last leg of life up the street a little ways. Finally bit the dust about 2 weeks ago and no problems since.

Problem solved!  Grin
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