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Author Topic: Stubborn RFI Problem  (Read 10594 times)
ND6P
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Posts: 103




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« on: August 13, 2014, 08:09:23 PM »

A couple of weeks ago, I started hearing what sounds like power line noise on 20 meters.  I tracked it to a set of poles two blocks away and asked the utility for help.  They did not find any problem there with the utility lines and think there might be a problem with a customer device in that area.

Here is what I know about the noise:

It is S9 when I point my beam to the suspected area
It never occurs at night
It may not occur at all for several days in row
The start time can vary from sunrise to late afternoon
After it starts, it stays on until late afternoon/ early evening
When it starts, it sputters on and off randomly for about an hour, staying on more and more until it is always on
When it ends, it sputters on and off randomly for about an hour, staying off more and more until it is always off
The noise is broadband and extends well beyond and below 20 meters

Anyone have a clue as to what the source of this noise may be?  Any suggestions for tracking it down?

Thanks ... Jim/ND6P
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KI6LZ
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Posts: 602




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« Reply #1 on: August 13, 2014, 10:04:53 PM »

I wonder if it was Tom that came out from SCE? He helped me with some arcing lightning arrestors.

The best way to characterize the problem is with a spectrum/waterfall display. This will show if the noise is really broadband or has some coherencies distributed at certain frequencies. It is useful to determine the bandwidth of the noise, in my case it was weak on 20 meters, strong on 15 and 12 and moderate on 10. The best way to determine direction is to use the antenna null rather the front to back since the null is usually greater. In my case I used the ends of the beam to null the noise and use that as the direction to start with.

I then use a CB mag mount antenna with a Grundig portable and drove around the area to find the hot spot. I got it to a couple of suspect poles which helped Tom out when he used his ultrasonic detector to listen for the arcing.

I tried using 2 meters with a 3 el beam but could not hear any noise with it, yes the detector was set to AM. Always listen to the noise in AM mode.

My power line noise 80% of the time was related to humidity, noise disappeared few hours after sunrise if not cloudy and appeared just before sunset.

Everything you mentioned sounds like it's some consumer device. My suggestion for the first go around is to use a portable SW receiver in AM mode and start walking or driving around the suspected area.



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ND6P
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Posts: 103




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« Reply #2 on: August 14, 2014, 05:30:02 AM »

No, it wasn't Tom.  I live in Burbank and have BWP.  They've been great about helping with this BTW.  Their communication specialist walked the area yesterday with ultrasonice equipment to check for arcing, finding none.

I have a pan adapter on my station and can see that it is broadband in nature.  In the RF spectrum waterfall, I see noise of the same amplitude that is evenly distributed in frequency.  In the AM decode waterfall I see energy every 120 hz., becoming weaker with each harmonic.

I tracked this first by using a portable short wave receiver in the car to find the area where the noise was the strongest.  Then I used a two meter hand-held in AM mode to survey the area.  I used an attenuator between the antenna and the hand-held to make signal strength readings of the noise at various locations.  I marked the readings down on a map and provided that to the utility.  I also listened on 440 but could not hear the noise there.

Now that the utility is saying that they think the noise is coming from a residence, I'm wondering how to confirm that.  And I'm hoping that someone has run into this type of noise before and can shed some light on what kind of device it might be.

Jim/ND6P
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KI6LZ
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« Reply #3 on: August 14, 2014, 10:19:12 AM »

Sounds like power line related noise if it is broadband and has 120 Hz components. Surprised that BWP would not investigate the residence since it could be a power related safety problem.

It's very difficult to identify a noise problem only by word description. Audio and spectrum plots are needed and even then most of the time no one can point to a specific source. There are too many, CFLs, lighting strips, grow lamps, chargers, solar panels, dimmers, etc. Some have the unique signature and others don't.

The timing of the noise is interesting, maybe a bad street light cycling.

If it's from a residence, the noise on a portable receiver should show a large increase there. You might be able to warn the resident that a potential safety problem exists and try to find the noise source by turning off breakers or asking what kind of devices are being used.
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KD0SFY
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« Reply #4 on: August 14, 2014, 10:37:39 AM »

Because of when it starts/stops and that it is intermittent at the beginning and end, maybe look for some kind of air conditioning/cooling system.  Those times would tend to correspond to when things are getting hottest.  Or, it may just be that a device is failing when it gets hot.
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ND6P
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Posts: 103




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« Reply #5 on: August 14, 2014, 11:52:59 AM »

BWP did try to access the residence yesterday but no one was at home.  He even spoke to a neighbor to learn more about how to access the residence, so he did not drop the ball by any means.  Turns out that the place is rented and that the renters do not keep a regular schedule of coming and going.  The utility rep may even go to the BWP records to learn more about gaining access (phone number for example.)

The topic of street lighting has been mentioned several times during the investigation.  The street has underground feeds to old-style street lamps that are on 8-foot pedestals.  The RFI peaks when I pass those with the VHF receiver BTW.  But then, the RFI peaks when I pass anything connected to the utility lines in the area.

I do agree that since I am hearing this noise some 1500 feet away at S9, there could be a safety issue alright.

I've tracked the noise against heat and humidity but didn't really find a repeatable relationship.  The weather here has been a fairly consistent for the last two weeks, being mostly hot and humid.  I haven't ruled out heat as being a factor however.

On the first day of the hunt, the utility rep connected his spectrum analyzer to my antenna to characterize the noise.  And we switched off the mains at my house to make sure it wasn't local.  Then we followed the noise to the same area that I had identified earlier.

The noise is not present today, so far.  When it comes back on, I'll go snoop around some more ...

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ND6P
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Posts: 103




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« Reply #6 on: August 16, 2014, 03:08:23 PM »

The RFI came back today, and it was 10 DB stronger, so it's now S9+10 on 20 meters.

I tracked it back to the same residence that was pointed out by the utility.

Here is what it looks and sounds like ...

http://youtu.be/AON3Xi03pi0

Any advice on what to do next?  I have an email waiting for the comm tech at the utility for Monday morning when he gets back to work asking the same question.

Thanks,

Jim/ND6P
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KI6LZ
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« Reply #7 on: August 16, 2014, 05:05:06 PM »

Sounds and looks like typical power line arcing noise. Nothing unique to identify it as something else.
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ND6P
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Posts: 103




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« Reply #8 on: August 16, 2014, 10:22:47 PM »

I think you are right. 

The noise has continued into the night today for the first time so I just went to the suspected area with a 4-element 2-meter beam and a handheld to see what I could find.  The VHF noise was very strong so I could not narrow the search to a single pole, but I did get it down to two adjacent poles.  I need to re-engage the utility person since he narrowed to a residence that checked out okay tonight with my 2-meter beam.  The utility person has a 5 element UHF beam.  I'm thinking that we can use that with my handheld to narrow further.

Interesting that he did not hear any ultrasonic noise there.  So hopefully the UHF beam will work out.

Jim/ND6P
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ND6P
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« Reply #9 on: August 17, 2014, 11:02:50 PM »

The RFI was really bad all day and into the night again so I went over to the suspected area with my old Sony Hi8 videocam and took some night shot video (IR).  I found arcing on two of the upper insulators and maybe on one of the cutouts.  I've passed the video to the utility ... hopefully this will be enough to get the ball rolling.

http://youtu.be/5NyNci5Zjpc

Jim/ND6P
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KI6LZ
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Posts: 602




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« Reply #10 on: August 17, 2014, 11:11:01 PM »

100 atta boys for finding the culprits. If you search this forum you will another ham who took a photo of an arcing insulator with a near 500mm telephoto camera lens. Wonder what kind of video cam you used.

Oops, read your post to fast. Okay on the Sony.
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W1RFI
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« Reply #11 on: August 18, 2014, 04:44:44 AM »

Ultrasonic detection is not the best way to identify sparking noise sources.  If the noise source were on the top of an insulator, for example, the insulator would block the sound and from ground level, the ultrasonic device would say that it is clean. Arcing inside a bell insulator can also be hard to identify, or arcing inside a transformer. 

The key is to use Radar Engineers signature-matching receivers to associate a noise source with a complaint, then isolate it to a particular structure using VHF directional antennas.  If ultrasonic is used, it should be one of the small detectors used with a hot stick by utility people inspecting the particular pile.

Ed Hare, W1RFI
 
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ND6P
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Posts: 103




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« Reply #12 on: August 18, 2014, 09:48:17 AM »

It's a Sony CCD-TRV67 with x12 optical zoom and nightshot.  I had not used the camera for many years and had trouble getting it to auto focus, as you can see in the video.  This morning I re-familiarized myself with the manual focus.  That would have worked much better.  I've been RFI lucky at my QTH for 20 years until this came along, so I've been on a bit of a learning curve.

I'll post a 'lessons learned' when this is resolved by the utility.  Thanks for everyone's assistance so far.

Jim/ND6P
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KI6LZ
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Posts: 602




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« Reply #13 on: August 18, 2014, 10:07:03 AM »

RFI: Seems to be a lot of confusion as to what the best method is in locating power line arcing. In my case with arcing lightning arrestors the problem was isolated by Edison using an ultrasonic dish receiver. The main noise was predominately between 20 and 27 Mhz. I tried a 3 el beam on 2 meters and a 8 el on 440 and heard no noise. So it seems that locating the noise is not as easy as described in most articles, including your observations on arcs that can be hidden from ultrasonic detectors.

There have also been comments on signature matching receivers not being very effective. I guess one need all the tools in order to find some arcing which can be missed by one tool.
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ND6P
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Posts: 103




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« Reply #14 on: September 14, 2014, 02:02:28 AM »

On Friday of this week, six weeks after notifying the utility of the noise problem, a lineman came to the power pole that is the source of the noise and tightened down everything.  Unfortunately, this did not stop the noise.  The insulators on the three HV lines are continuing to arc.  I was just there this evening and can see the arcing taking place.

The scope trace of the noise below was taken today from my shack.  I'm noticing groups of three or two arcs spaced at 8.3 msec.  8.3 msec corresponds to 120 cycles per second and is typical spacing for power line noise.  If the three HV lines were phased at 120 degrees, the individual arcs would occur every 2.8 msec.  So what's getting my attention is how close the arcs in a group of three are to each other.  I'm wondering if there is a phasing problem on these lines that is causing excessive high voltage between the HV lines.  Does this make sense, or is there another explanation?

https://www.flickr.com/photos/60233434@N05/15046754238/

Jim/ND6P
« Last Edit: September 14, 2014, 02:21:41 AM by ND6P » Logged
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