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Author Topic: finding RFI sources in dense urban environment  (Read 15329 times)

Posts: 17

« on: January 20, 2013, 04:55:41 PM »

I live in the middle of a city, so I realize a certain amount of resignation is called for when it comes to RFI. But if I walk literally one block over, in a couple of different directions, the noise level drops 8 or more S-units. If I walk up to the park two blocks away with the ft817 and a whip antenna I can hear crazy amounts of HF activity, and as soon as I'm back in front of my house I hear _nothing_ because it's all lost in the noise. VHF/UHF are generally fine.

I don't think much of it is coming from my house, because even when the power was shut off for electrical work, it didn't drop noticeably. Walking around with a radio reveals just a very gradual drop-off in various directions, but no obvious individual sources.  I wonder if it is being radiated uniformly by power lines running along the streets, or from *every* telephone pole, or what. I'd hate to think it's just one wall wart somewhere that could be unplugged to solve the whole problem. Smiley

Any suggestions on how to narrow it down directionally, particularly when it may not be a point source? It seems impossible, but maybe there's a way.

Posts: 0

« Reply #1 on: January 22, 2013, 08:03:01 AM »

I would call the local power co. and tell them you think you are getting rfi from their power lines and they will send someone out to check it. They should be able to narrow it down.

Posts: 14499

« Reply #2 on: January 22, 2013, 08:48:08 AM »

As a general rule, most power line noise travels much shorter distances along the lines at VHF than it does at lower frequencies. A 2M receiver that has an AM mode will usually allow you to walk along the power lines and get an idea which pole(s) are creating the problem. MFJ has (at least the used to) a hand-held VHF noise detector. Add a loop or small Yagi antenna to make it easy to pinpoint the noise direction.

I once had a noise problem on HF and broadcast band that just seemed to be coming from everywhere. I could tell that it was radiating from wiring inside the shack. With a VHF AM receiver I located the problem about a mile down the road. At lower frequencies it was following the power line all the way back and into the shack. It turned out to be an abandoned 1-foot piece of wire and a loose bug that was arcing when the wind moved the wire. The power company came out and removed the abandoned wire and everything went quiet.

Bob  AA4PB
Garrisonville, VA

Posts: 5

« Reply #3 on: February 13, 2013, 12:39:48 PM »

I just found a continually arcing lightning arrestor on the 7200v overhead lines with the help of the local utility.  I pinpointed it  first ( about 1 mile west of my house) , and called them out.  It wasnt on the first pole we tried but it was on the second pole.

The rubber boot around the spark gap in the arrestor had blown open  all the way around, and you could hear the continual arcing across the gap  from ground level right under the pole in question.  A new arrestor and  insulator  on the 7200v line and no more problems. 

With more homes come more service line drops and arrestors and more chances for loose hardware, loose wires, etc.  Keep walking and map it out.  Google maps are a great way to  identify  poles in question and keep track of what youve surveyed. Each pole should have its own number  labeled right to it.  Get that info and call out the utility.  Dont just call them and take your chances. 

Also, anywhere you see  power lines running THROUGH tree limbs and branches/twigs, notify the utility. They are powerful sources of noise, and the utilities are  required to keep their lines clear.  The major power outages have put many of them in  hot water with the government.   

Look for  loose wires, chains, and other items hanging on the power lines.
80% of  RFI from PLN is reportedly due to loose or defective hardware.

Anytime a lineman comes out, make sure he goes up in the bucket and tightens all hardware while he's up the pole you think is a problem.  Some are too lazy to go up.  Ask them to and they usually will.

Posts: 12

« Reply #4 on: February 18, 2013, 10:29:10 AM »

I would call the local power co. and tell them you think you are getting rfi from their power lines and they will send someone out to check it. They should be able to narrow it down.

anybody ever hear of LIPA  Roll Eyes 
well ever since hurricane sandy, i've had 20 over S9 noise on 40m, & S7 noise on 20m.   24 hours a day, every single day.   they USED to be FAR quieter.  10 & 12m, while i THINK are noisier during the day then they should be, ARE noisier on my ic 746pro then 10m is on my ft101e & 11m is on my uniden grant xl.  after dark, my icom is as quiet as it should be on 10 & 12m.  the weather is just not conducive to playing with my end feds on the roof & in the trees right now.  my par 20m & 40m both came down in the storm & are remounted differently then before.  i've shut the house power off & run the icom & xl from a battery & noticed ABSOLUTELY NO DIFFERENCE in the noise on the icom.  i'm HOPING that MAYBE the proximity of the feeds on the par's to other metal masts/antennas could be causing the noise on those 2 bands?Huh?
back to LIPA...with more then a few telephone poles near me sporting hanging & dangling wires since the storm repairs were completed, i thought MAYBE something could be causing the noise???  well, i haven't been able to speak to ANYONE at LIPA that knows what amateur radio is.  i haven't been able to speak to ANYONE at LIPA who can even begin to understand what i'm talking about or what dangling wires could cause interference with or even why i'd be concerned.   so.....calling the local power co was USELESS!!   
anybody have any idea how/why/if my endfeds could be causing the noise due to closeness to other antennas, water in the matching box, bad matchbox, etc?

Posts: 105

« Reply #5 on: February 20, 2013, 08:33:19 PM »

As a former RFI/TVI troubleshooter for a power company, when trying to find the problem, remember that the utility's responsibility ends at the meter...if you turn off your main disconnect at the meter (I hope you have one...some older houses I came across did NOT have a main after the meter..only the box with individual circuit breakers...which in that case you need to open all the breakers) and the noise goes away, it's your problem. Do not do anything that you are not qualified for...(some folks will open the panel while it's hot though they know NOTHING about AC wiring, etc..been there, seen it happen) piece of equipment I used (among others including a VHF AM rcvr and IFR spectrum analyzer) was a cheap ordinary pocket AM radio..the ferrite bar antenna in bi directional so if you can null the noise, take readings from a couple of spots and see where the nulls intersect...IF it's a neighbor's house, do NOT offer to fix their problem. You can get into a lot of legal issues with that. Talk to them first and if they get it fixed, fine..if not, then getting with the nearest FCC office is your next option.

One day I need to write a book on all what I found but the FCC seems to care less about LF/HF etc....(which is why they are trying to push public safety, etc to 700/800MHz bands...BUT they don't work well at all in pine needle country...and in East/SE Texas, we have a lot of them  and no mountains where the repeaters could at least cover worth a flip Sad
(here we have 2000ft towers instead but all in the wrong places...and hurricanes/tornados like to eat towers sometimes)
Add to that the issue of the FCC not having enough manpower or money in their budget to keep up with all the issues, life on MW/HF is going to get worse...(at least BPL died..I hope)

Posts: 1965


« Reply #6 on: February 20, 2013, 10:16:46 PM »

One day I need to write a book on all what I found but the FCC seems to care less about LF/HF etc....


I have found just the opposite...  The FCC has issued take down notes in the past, and corrected RFI issues for me...  They seem responsive, and they seem interested...

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