Odd noise problem

[W1RKW]

Got an peculiar noise problem.  It's an impulse type noise at 60cps like that of a dimmer switch. It's not coming from my house or at least I think it's not when the main breaker is turned off. I get it on 75m on the FT102 w/75m dipole and on a battery operated portable SW receiver inside the house. Take the portable outside and nothing but it's inside the house even with AC cutoff to the house. Also get the noise on the 75m dipole using the portable receiver outside.  Turned the UPSs off as well and nothing. Walked the neighborhood with the portable receiver tuned to 75m and all is clean. If I walk the perimeter of the house (outside), no noise.  Followed the underground power line to the transformer, again clean.  I'm stumped and ready to give into getting one of the outboard DSP filters but not sure if they would work on this type of noise. No other band exhibits this. Any ideas or suggestions anyone?

[WQ9E]

Check near your phone line to see if it is riding in there.

[Mike/W8BAC]

Sniff near the power meter? Water Meter? Cable connection? Wat about DSL?

Mike

[K5UJ]

Noise can be conducted via power lines.   I have a similar situation at night so I suspect one or more street lights.  The sodium vapor lights can get noisy like what you describe.  

If it is coming in on your service drop you can actually put large clamp on ferrite cores all the way around them, you have to be sure to circle the two hots and ground when you do this, and if successful they can attenuate noise coming in.  

You can google RFI Noise recordings and get a link to a website now hosted by ARRL that has recordings of noise from various sources to help ID the cause.  never mind here it is:  http://www.arrl.org/tis/info/HTML/rfi-noise/

Jim Brown's paper on noise is also excellent and addresses many causes and solutions.
http://audiosystemsgroup.com/RFI-Ham.pdf

Rob

[K5UJ]

I miss-read your post, sorry.  The dipole can pickup the noise when the portable doesn't if the dipole is not parallel to the source.   It is counter intuitive but I discovered this in reading two papers that were in QST in September 1995 on p. 33 and 37.  The first one is by Beezley K6STI , A Receiving Antenna that Rejects Local Noise, and the second one is by Andress W6KUT, A K6STI Low-Noise Receiving Antenna for 80 and 160 Meters.   A horizontal dipole will pick up the noise best if it is at a right angle to the source.  I can't explain why but Beezley does in his article.  I agree that it is finding a way in when you flip the house breaker off so you should check the other paths in.  I have noise issues here so I've been doing some reading lately (75 m. was incredible this morning however--super low noise level--if only it could always be like that.)

A DSP filter is a last resort and not a very good solution because they almost always introduce audio distortion.  If you can't fix the cause, it is far better to employ a rx antenna that doesn't pick it up and/or a phase shifting nulling box like the one made by MFJ:  http://www.mfjenterprises.com/Product.php?productid=MFJ-1025

[K1JJ]

Bob,

Take a long ride around the neighborhood out to at least one mile or more.  Turn on the car AM radio to a clear spot (up around 1700 khz) and turn up the volume. This will tell you the story.  You will hear all kinds of noises. Most of the problems come from splices on the power lines - and insulators breaking down.

The problem could be:  Power lines sometimes run long distances in a straight line and the length can add up to a long wire antenna with big gain off the ends.  On my street, we are at the end of a 1/2 mile run of straight power line run.  I can often hear arcing that is a mile away simply cuz it has been enhanced by the gain. When I drive to the source, it is not that loud, so the power company wudn't bother to fix it.


Does the noise level change as you sweep up and down the 75M band at home? If so, this is the effect of the power lines "antenna" phase adding and canceling its lobes in your direction as freq changes.

I was told this theory by one of the well-known antenna gurus. It seems to pan out, at least in my case.

Drive around and do your detective work.

T

[W1RKW]

Hey guys,

thanks for  the input.  

I'm not sure that it would be a street light since the nearest one is about a 1.5 miles away but then again who knows.  The noise does go away intermittently but I have not been able to correlate to weather or anything else.  Checked the electrical service drop right up to the meter and out to the transformer that is on the corner of the property.  The phone service runs parallel too it and they're both underground. No cable here. Did this with main breaker on and off using the portable receiver, no noise.  I only get the noise on the 2nd floor with the portable. It's weaker on the first floor and not discernible in the basement so that tells me its way above ground where the portable does not "hear" it at ground level and below. This might explain why I only get it on the 75m dipole in the shack.  I've driven around the surrounding area with the portable but again it's quiet where ever I go. And it only seems to be on 75m. 160 and 40 are quiet but I don't have resonant antennas for those bands so that maybe part of why I'm not hearing it anywhere else.  AMBC band is quiet too.

Tom,
the buzz is pretty much a constant S9 over the entire 75m band. Rolls off slightly to S8 at the low end.

[W1RKW]

Listened to some of the recordings.  This noise is a cross between a switching power supply and a dimmer control.

I'm going out in a little while.  I'll take the portable and use the AMBC radio as well to see if I pick up anything.

attached is a map of my route from previous sniffs.  "A" marks the w1rkw qth.  Most of the terrain is woods and open fields with a few small neighborhoods off of Rt 16.

[W1AEX]

Any chance you could make a short mp3 recording of the noise? Does it change or go away in wet weather? Tracking this stuff down can be an exasperating task, but it's something that happens to everyone at some point in time. My last run-in with a nasty noise issue was two summers ago, and I found the general area of the problem by doing what Tom suggested, driving around with the car radio tuned to an empty frequency at the top of the AM BCB. I also used the trick of connecting my 6 meter beam to my 75 meter receiver and got a good compass heading by using the null and the peak as I rotated the antenna. That brought me (and the power company) to a blown lightning arrestor about 3/4 of mile away.

As a defensive measure against noise, you might want to construct a couple of small triangular loops on the edges of your property, using the SW portable to locate nice quiet spots. I used the dimensions of the K9AY type loops (about 85 feet of wire) and threw a line up to a branch about 25 feet up in air to haul up the peak of the triangle, then tied off the bottom ends of the loop to convenient trees to form the base of the triangle (about 30 feet in length) and fed it in the center with a 9:1 transformer made from a little flea market ferrite donut core. I use about 300 feet of cheap RG6 to feed each of my receive loops. One loop is oriented to receive north/south and the other receives east/west and between the two of them it is blissfully quiet when my wife is playing with the paper shredder, microwave, food blender, eliptical trainer with noisy programmable computer, or whatever else is amusing at the moment. The loops are cheap to make, quiet, untuned, broadband, and quite directional from the BCB through 75 meters. They are very good for general SWL on the upper bands, but don't show much directivity above 75 meters.

Anyway, good luck, and I hope you track down the noise successfully.

73,

Rob W1AEX  

[W1RKW]

K1JJ is a radio god. I had my doubts about using the AM radio in the truck because of fuel injector noise but tuned the radio to 1710Khz and that was the ticket!  The noise was so strong outside it buried the fuel injector noise from the engine and that was just in the driveway. The noise is coming from 1 of 2 homes down the street and man is it loud.

Went back home to tune the receivers.  It's very strong, 30 over S9 on the FT-102 at 1705 and that's on the 75m dipole.   It's quiet from 1690 down on the car radio. I thought I tuned the FT102 down that far but maybe not.

Now the fun begins.

I'll try to capture it as an MP3.

[N2DTS]

I have a nasty impulse noise right on 3880, plazma TV I am sure as it sometimes is gone, then pops on.
Whoever has the TV seems to have it on a LOT!

Brett
 

[Jim, W5JO]

If you hear noise on 160 and 75 meters it can be a long distance (several miles in some cases) to the source.  The closer you get to the source the higher frequencies will find it.  So start as Tom says with your auto and drive around until you get a strong signal.  Then, if you have some sort of receiver with 10 meters or the Aeronautical band which AM,  the noise will be stronger on the higher frequencies as you get very close. 

So as you get closer, move up in frequency with your radio.  If you have some sort of portable with the Aircraft frequencies you will almost pinpoint the pole.  Don't be banging on the pole, wires can fall, just get the number on it and report it to the owner.

[K5UJ]

Cracked lightning arrestors on power poles seem to frequently be the problem. 

I worked a guy last weekend, he was in Cincinatti (I may have already told this story) and he recounted a recent 160 m. noise episode in which he suddenly had 20 dB over 9 noise all across 160.  Made operating it impossible.   He got out his DF gear, I think he had a small yagi and AM aviation band rx, and eventually got it down to a house 1.5 mile from his QTH.  At that point it was so strong it swamped out AM broadcast stations.  Knocked on the door.  Man answered door.  Our ham explained that he couldn't even hear the local 50 Kw broadcast station up above 1500 KHz because of interference he traced to this home, and asked if the man had purchased anything electrical in the past two days.  Man says, sure I got a TV recorder (one of those tivo type things) from the cable company.  He was asked to go inside and turn it off just to check to see if it was the problem.   The guy goes in and unplugs it and the noise vanishes.  Our ham told him there was something seriously wrong with it and he should get another one because it might start a fire if he continues to operate it.  As far as I know that was the end of that.   

[W1RKW]

I'm pretty sure or convinced the noise is local to my street. No noise at 40m and higher.

[Jim, W5JO]

If you don't hear it on 40 and up then it probably is farther away than in your or your neighbor's houses.

[WQ9E]

My location is normally very quiet but there have been a few times where QRN has suddenly popped up and made conditions horrible.  My full wave 80 meter loop seems very sensitive to any noise on the power lines so I have been trying some solutions for the intermittent noise. 

I bought an MFJ noise canceler and at times it makes an amazing difference but it is necessary to provide it with a source antenna that mostly picks up the noise and not much of the desired signal.  It is pretty touchy to adjust.  Most of the time a small directional loop seems to work very well and is easier to get good results.  I have been playing with the directional bar antenna from a marine direction finder and the AL-4 loop that came with my Drake  SW-4A but I think building a slightly larger loop may be the ticket.

Although the best long term solution is to get rid of the noise at the source I have a feeling with all of the garbage products being sold it is going to be more practical to have strategies to minimize the problem at the receiving end.

My usual noise level on 75 is around S-3 so it is really annoying when some S-8 to 9 noise pops up.

Rodger WQ9E