RFI

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My Hunt for RF Noise

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Original Page drafted February 20 2005

I live in Arlington Virginia. I like to listen to the radio, but, my radio reception has been suffering from what I believe may be power line noise. I can hear this noise on a fairly regular basis, and it affects reception over wide portions of the radio spectrum. This web page is intended to help document this problem. It will be updated over time, as I gather new related information.

Meet the Enemy

The following files were captured using DL4YHF's Spectrum Lab Audio Signal Analyser software.

Audio File: February 20 2005 ~1350z
http://brauhaus.org/n8ysz/rfi/20050220_1357_capt.jpg Image:20050220 1357 capt.jpg

I noted strong repeating peaks at 120hz intervals. This was captured at home, in my kitchen, using my laptop connected directly to my aging Sony CFS-210. The radio was tuned to the midst of the AM broadcast band. The weather was cold, partly cloudy to overcast, but dry.

This has been an on and off problem for me for quite a while. Up until now (February 20, 2005), I haven't tried to log or chart the problem - it does come and go, but has recently been getting progressively worse.

In diagnosing this problem, my first guess was that I was causing the interference myself. Both my wife and I are computer users - our house is networked and we tend to have multiple machines running at any given time. I have attempted to follow a process of elimination by turning each machine off in turn, listening to see if the noise abated. While I did find each computer, monitor and peripheral had a characteristic sound on the radio, I didn't find THE cause of my misery.

My next step has been to use a portable battery powered AM radio and walk around the house, searching for noise. For this, I used my Sony ICF-2010 shortwave receiver and a pair of headphones. During this search, I did find a number of other sources of noise, inside my house. Each of the X-10 light switches and outlets were radiators, as were each of the dimmer light switches. One of the worst was the switch that controlled the ceiling fan and light in our front entry way. I also found noise from all of the florecent lights in the house - especially bad was the compact florecent lighthood over my salt water fishtank.

Still - even with all of these sources turned off, I can still hear the noise! I haven't yet flipped the breaker for the entire house, but this is on my list, just to be 100% thorough.

For those who'd like to follow along at home, try this:

First, listen to the the audio on the webpage above. Then, get an AM radio. AM, not FM. Tune around the band, listening "between" radio stations. See if you hear something similar - a rhaspy buzzing or hum. If so, you may suffering from similar RFI. According to the documentation I've read (see links below!), the noise will be worse closer to the source of the problem.

My suspicion is that I'm suffering from powerline noise. By walking and driving around the neighborhood using a portable radio, I have found a couple of transformers on poles not far from my house which seem to be the major noise source near my location. Unfortunately, I have a feeling there may well be multiple sources. I live in an older neighborhood with raised power lines. We have lots of trees - many of which are close to and, in some cases very nearly touching, the power lines.

I filed a report to Dominion Virginia Power, using their web email form, on February 19th. I am waiting to hear back from them.

Update February 21 2005

Dominion Power received my web-email submision and replied with: 

The Dominion Customer Service Center has received your inquiry.

Dear Mr. Brown,

Thank you for your email.  Your interference has been reported.  Your work
request number is ########. 

If you need further assistance, please call our Customer Service Center at
1-888-667-3000 to discuss your inquiry. The center is open 7 AM to 7 PM
Monday through Friday and 9 AM to 1 PM on Saturday.


I heard the noise tonight on both the 2010 and 210 receivers. Weather has been rainy and overcast.

Update February 22 2005

After drafting this web page, I had sent an email to Mike Martin of RFI Services, with a pointer to my noise sample. He responded today saying he doesn't think that it is power line noise. I will be contacting him again in the near future. Updates to follow.

I noted tonight that the noise seems to have faded. I was, again, able to find my various dimmer switches and my laptop, but not the same noise I recorded the other day. Also noted, the kitchen dimmers do sound similar to the noise I'm trying to track down. Tonights listening was done using both the 210 and 2010 receivers. Weather was cloudy, but it has been dry for most of the day. We've had rain within the last couple days. Noted this morning that I could make Spectrum Lab go into oscillations if I adjusted the volume on the laptop just right.

I recorded a couple samples of my laptop, first on AC power than on DC. The recordings were done with the ICF-2010 shortwave set tuned to 784.3kHz Wide AM. I was using the internal ferrite loopstick antenna.

The laptop has noise at 100hz intervals - constant while on AC, and periodic (though not at even periods) while on battery. I'm using a Dell Lattitude D600. It is set to turn back CPU performance when not on AC power.

Update February 23 2005

The noise appears to be back this morning. I heard it on the kitchen clock radio, all over the AM broadcast band, when I checked at around 7:15am. I confirmed that I can hear it with my kitchen dimmers, bedroom X-10 and front porch rheostat all turned off. Weather was low 40's, mostly clear and dry. There may have been light precip. over night - my car windshield had water droplets on it.

I talked to Mike Martin of RFI systems this morning. He had listened to the sample I posted, and told me what he is hearing sounds like a dimmer or a touch lamp, not power line noise. I sent another email to Dominion to have them call of the dogs for now. Many thanks to Mike for the prompt call back and helpful advice!

As a side note, in thinking about this, we have experienced problems with both our cable TV and our DSL line at various times in the past. We seem to lose the signals from the provider (dsl or cable). On our digital cable, this sometimes means we can't view higher channels or have a hard time getting the "guide" down. We had a cable modem for internet for a while, but that proved to be too much hassle. There were just too many losses of service.

I later switched over to DSL when it became available in our area. It has been fairly stable. When we first got started, however, we had a lot of problems until I disconnected almost all of the interior house phone wiring and ran a special Cat-5 cable for just the DSL box and the one phone drop we use in the house.

During hurricane Isabel, we had a large tree come down across the power, cable and phone lines, which run across our back yard. This severed all of these lines and pulled the service drops off the side of our house. All have been since repaired, though, the cable tv drop still needs some work.

I have to wonder if these all of problems aren't related.

Update February 26 2005

Did some more monitoring this afternoon using my Icom 706IIg and my PAR 50mhz moxon. The noise was going strong again, and I got a couple more audio and spectrum captures of it. Using the moxon, which has a fairly deep null off the back side, and a hand held compass, I noted that the noise appears to be coming from almost directly east of me.

I set Spectrum Lab up to be a pass through, and hooked the audio output from the computer into my Tek 2225 oscilloscope. Spectrum Lab conveniently has a signal generator, which, after temporarily switching off the ADC input from the radio, I used to get the scope adjusted to a reasonable display of the audio waveform coming out of the computer. Switching the ADC input back on and the signal generator off, I was able to see the noise waveform on the scope. This allowed me to get a general measurment (6ms) of the spacing between the noise pulses. Spectrum Laboratory does have a "time domain" display, but that display lacks graticules - the graph lines across the screen.

When the noise is active appears to be somewhat cyclical, though there seem to be multiple patterns to the cycle. In one pattern, the noise wave form varies between 1, 2 and 3 peaks and then back down, 3, 2, 1. By ear, the intensity also appears somewhat cyclical, though this may be more related to how I hear to the change of the tone, rather than any actual change in intensity.

Spending some time switching bands, up and down, I'm beginning to believe that I hear 2 or more different noise sources - one more overall than the other. This is especially evident switching between listening on 50mhz and 28.500mhz. Its also pretty easy to see this on the scopes - both Spectrum Lab and my Tek.

The weather today is calm and clear, the temperature is in the mid 40's.

Update March 4 2005

Heard another ham talking about RFI this morning, on the air. Almost jumped in to ask where he lives - Turns out I should have!!! I looked him up online and he's right around the block from me. His qrz.com listing doesn't provide any email address or phone number, so I'm going to need to send him something snail-mail or go knock on his door.

Please!!! If there are any hams reading this, who are in my area and who'd like to give me a hand finding this problem, please contact me. My qrz.com listing has my contact information.

Update Apr 2005

Talked to the other ham on the air - he didn't live as close as I'd thought - too many streets with the same names up here.

Update June 6 2005

After nearly 5 months of waiting, I got a call from Ken Lyons of Dominion Power, who is going to come out and take a look/listen to the problem.

Update June 7 2005

Ken Lyons arrived this morning. I found the noise on the clock radio in the kitchen and played it for him. He went to work, starting by pulling out a small AM radio then heading to the breaker panel to isolate things in the house starting by shutting off the mains. That killed most of the noise on his radio immediately. He then worked through each of the breakers and found that the worst of the noise in the house was coming from the dimmers in my kitchen. No big surprise there. I was starting to worry that he thought he'd found the problem, and was going to leave, but then he asked about my "two way gear."

We went out to my office and listened on my '706 with the kitchen still powered off. After I reconnected the antennas, which had been disconnected for the previous evening's thunderstorms, we were able to hear the noise. As always it was across many frequencies from low HF all the way up through 50mhz and 144mhz. I flipped through frequencies, and showed him the display of SpectrumLab, which had the signature indications I'd come to expect - lines at 120hz intervals on the spectrum display and the jagged waveform on the o-scope display. At that point, I believe I'd convinced him that there was an issue. I pointed out my antennas and told him I'd been able to use the null off the back on my PAR 6m moxon to get a general bearing on where the noise was coming from.

Ken decided that it was time to go drive around and hunt for the source. He found the noise using his monitoring gear in his van, and we headed down the street from my house. The noise faded as we got to the bottom the hill. We turned the corner and headed up back up, around the block. The noise was apparent as we drove under some overhead lines and as we drove past a couple particular light poles - all consistent with what I'd discovered previously walking the area with my portable radios.

I directed him to the area I'd located as having the strongest apparent source of noise - the couple of poles not far from my house, each with a transformer and other gear on them. He confirmed, using his equipment, that the noise was strong there. He turned up the RF attenuation and noted we could still hear the buzzing, even with maximum attenuation. We drove on past the poles a bit and the noise faded. Again, this was consistent with my previous findings and an indication that we were close to the source. He turned around, drove back up the street and parked by one of the poles.

Ken got out, and using a small receiver with a yagi - a directional antenna - further confirming the noise was indeed coming from this particular pole. Next, he got a small sledge hammer from his truck and, pounding on the pole, (which is DANGEROUS and NOT recommended for anyone other than power company personel!!!) worked on determining whether the hardware on the pole was loose and needed to be tightened. I don't know if he decided whether that was indeed the case, but it did sound to me as if the noise fluctuated some when he hit the pole. This was a relief for me, as it should be a fairly easy thing to fix.

About this time we also noted that we could hear, without any equipment, a buzzing noise coming from the pole. Ken got a different device - one with a microphone and a parabolic dish, and attempted to determine which bit of the gear at the top of the pole was specifically at fault. If I understood correctly, he was hearing the noise from the whole general area at the top of the pole, so couldn't isolate anything in particular.

He decided to flag this as a trouble spot and to call in a linesman to take a look. ETA, probably a couple weeks or so, depending on availability. He drove me home, I thanked him and he promised to be in touch on when they come out to do the work. Mr. Lyons said he'd like to be there when they did so that he could determine whether the problem was actually solved.

Here are some links to related information which I found useful:

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