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Author Topic: Diagnosing Power Line Noise  (Read 4574 times)
AA6CJ
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« on: October 13, 2009, 03:16:32 PM »

To all:
S5-7 noise level from 80-10m.  Well, that's the big problem.  I've tried eliminating power to my house and that didn't fix it, though I've found many little noise sources within the house...none are so big as to fix the main noise problem.

How can I determine for sure that its Power Line Noise?  What is the procedure for isolating the noise, and how far away from my home should I be investigating?

Lastly, is there something I can buy that is effective against power line noise (like MFJ 1026 or ANC-4)?
73,
Fred
AA6CJ
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WB5JEO
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« Reply #1 on: October 14, 2009, 06:59:52 AM »

It's likely not very far away. A common problem is a broken ground lead at a transformer. Another is simply a defective transformer. I had an intermittent problem once caused by build-up of lint from a nearby cotton gin. In high humidity, it would create a poorly conducting path to ground. Went away when it dried up and after a rain hard enough to wash it off. It was mostly seasonal at ginning time. The defective transformer was pretty easy to locate, since the beam  clearly indicated direction. If there is only one transformer in the area, it's a good suspect. The trick is convincing the power company that it's there. It's not that they're opposed to fixing it. In fact, most will deal with it, because it suggests that the transformer may fail, and a broken ground lead is something they want to fix. Any sort of reasonably accurate direction finding or a clearly stronger signal on a portable when near the pole should be enough to get them to check. It helps if you can be there to demonstrate it for the tech. They may also have one or more means of testing for faults. Some analyze gasses generated in the transformer fluid. Others do other analysis on the fluid or work off features of the current. If the transformer serves only your house, they may even take it out of line to see if the noise stops. No processing is going to do much with that kind of noise, not in any way that you'd want to live with.

In an urban commercial environment, neon sign transformers may be offenders. They just have to be run down by D-F or the portable receiver. If anyone happens to have a well-designed HF receiving loop, it's a great help locating any of this sort of thing.
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WX7G
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« Reply #2 on: October 14, 2009, 07:28:23 AM »

Shutting off the AC power to your house is the experiment that reveals that the noise is not conducted to you via the AC outlet. Line filters on your radio will not help.

You can look for the noise source using an AM radio.
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WX7G
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« Reply #3 on: October 14, 2009, 07:33:13 AM »

Take a look a the eham reviews of the MFJ-1026. It appears to be quite effective.
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AA4PB
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« Reply #4 on: October 14, 2009, 11:12:22 AM »

ARRL has a great book "AC POWER INTERFERENCE HANDBOOK" that can answer all your questions.

Most of the time the problem is caused by defective insulators and connections up on the poles.
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W5DC
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« Reply #5 on: October 14, 2009, 11:51:35 AM »

One thing you can do to be a bit more sure that it's power line noise, although other line synced noises will still show this, is to put you ham receiver on am and look at the output on a spectrum analyzer of some sort.  If you don't see a harmonic series of line frequency or 2x line frequency, then it's not power line or line synced.  This can also be a good way to adjust noise blankers.

73, Dunc, W5DC
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N1UK
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« Reply #6 on: December 29, 2009, 06:38:34 PM »

I have used the MFJ-1026 and it knocked down my power line noise quite considerably. The secret to getting it to work is to have a sense antenna that picks up as much noise as your main antenna if not more. I would recommend the 1026 over the 1025 as the 1026 has a built in amplifier which helps to boost the signal from the sense antenna. In my case I had the sense antenna sitting quite close to my noise source and my main antenna was quite a distance from the power lines.

The amplifier in the 1026 is noisy on 10m and limits low signal work on that band.


Mark N1UK
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KB4MB
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Posts: 295




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« Reply #7 on: January 03, 2010, 03:05:23 PM »

I feel stupid for bringing this up, but just figured I would so it is documented somewhere.

I did all the steps you did, convinced it was a powerline issue - however, the noise didn't change when I disconnected the outer connector on the pl-259, only when I disconnected it.  This then we diagnosed as a bad feedline (ground, of course).

Ashamed because it was something so easy.
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AA4PB
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« Reply #8 on: January 04, 2010, 05:50:15 AM »

Probably the most common cause of power line noise is arcing insulator hardware on the poles. Often the noise comes and goes with changes in the wind and humidity. The only fix is to get the power company to come out and check it.
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K0BG
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« Reply #9 on: January 04, 2010, 07:53:30 AM »

I'm with Bob, AA4PB, on this one. Whenever you cure your noise using a noise blanker, or some external device, the receiver dynamics just go to pot. It is always best to fix the source.

There is another related issue, and one a lot of folks have without even knowing it. If the antenna in question is inherently imbalance, whatever the cause, there will be common mode current on the feed line. If this is the case, RF can get in via common mode too. This fact exacerbates noise problems from localized noise sources. Just because you don't have RFI problems caused by the common mode current flow on transmit, doesn't mean very much.

Look at this site for more info: http://audiosystemsgroup.com/publish.htm

Take your time as there is a lot of data to digest.
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N2HO
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« Reply #10 on: March 22, 2010, 08:26:31 AM »

Last several months I experience severe (S9+) arcing  noise (sounds like continuous popping noise) which depends of the weather condition. When there is a nice dry weather the interference is there while during the rain or high humidity I have no problem. It not depends of the time of the day and somewhere around my house in a circle of a couple hundreds yards, but I cannot pinpoint a specific electrical pole so far. I tried to watch visually at the evening walking around but with no success, and no audible spark discharge sound. I also walked around with portable HF receiver but it didn't help to find any specific electrical pole.
What I'm asking for is: if anybody in my reach (US north east) has some equipment to borrow to help me to find the particular power line noise source? There were some projects in QST like ultrasound power line arc detector (QST 4/2006 by W1TRC), but I decided to ask here before I start to build something. Any help would be appreciated. My email is n2ho<at>juno.com.
Thank you.
George, N2HO
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AA4PB
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« Reply #11 on: March 22, 2010, 09:30:50 AM »

I noticed that the power company techs use an AM receiver in the VHF/UHF range for tracking down interferrence. The shorter the wavelength, the less distance the signal will travel down the wires. It also alows them to use a hand-held Yagi antenna for direction. In one case I found that source of interferrence (on HF) to be about a mile down the road so it can travel quite a distance at that frequency.
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WX7G
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« Reply #12 on: March 22, 2010, 02:18:08 PM »

The power company should have a person to track this down. Give them a call.
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W8JI
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« Reply #13 on: March 25, 2010, 09:03:15 AM »

http://www.w8ji.com/power_line_noise.htm
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N2HO
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« Reply #14 on: March 25, 2010, 02:12:41 PM »

Thanks everybody for advices, I met Bill (AB2UW), who has experience and necessary equipment and willing to help, and I hope we'll find and fix the problem soon.
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