Help identifying broadband noise source

Kevin LaFata

All though I've asked in another place, I was hoping some Flex users might be able to shed some light on this.  I've had some broadband noise appear several days ago that affects most of the HF bands. A video of the waterfall is below:

https://www.youtube.com/watch?v=HjV8_DWYmnE

I've tried turning off all power to the house and UPS devices. The noise continues.

It is 24/7 so not likely a neighbor's plasma TV

I went portable and operated 3 miles away and the noise was gone

I've used two different antennas in two locations and the noise stays the same.

I've used an RTL dongle on the laptop (with 125Mhz up converter) with same antennas but don't see the noise (I can't explain this one at all). SSB signals come in fine.


I'm thinking about making a Yagi and going out to do some direction finding if there's nothing else obvious.  My guess is a power line somewhere.  Has anyone else come across this before on a Flex?

https://www.youtube.com/watch?v=HjV8_DWYmnE

Stu Phillips - K6TU

Kevin,

A quick test to see whether its power line noise is...

1. Put the slice in AM mode - filter width is not important - this gives an envelope detector
2. Record the noise using Audacity or similar audio tool - Audacity is free, works on Mac & PC
3. Zoom in using the spectrum tool until you are down in the millisecond range

If the noise is power line generated, your will see 8.33 mS between noise spikes - 8.33 mS is 1/120th of a second...  power line noise is caused by arcing and there are two voltage peaks per cycle at 60 Hz - so the arc is generated on both positive and negative going AC peaks - hence the 120 Hz rate.

If you use the latest version of SpectrumLab, it has a digital oscilloscope mode that allows you to capture the patter on the arcing...  a specific source of power line noise will have a pretty repetitive pattern so it helps as you go hunting to figure out whether you have found the right pole or not.

Whether power line noise or not, DF it at HF and see where it is strongest.  If it is power line noise, as you get closer, go UP in frequency.  When you find the right pole you will hear the arcing at least to 150 MHz, sometimes even higher.  If the pole isn't "hot" on VHF, its NOT the right pole.  Keep looking and remember that the noise will set up a standing wave on the power lines which will have its own peaks and nulls.

If you get to a pole and find that all directivity of the noise has disappeared, this is also a clue that its NOT the right pole.  Keep walking.

I can't really tell from the video what you are dealing with - between the frame rate of the spectrum display and the frame rate of the video capture/playback, its too jumpy.

Last but not least...  its fun to speculate about the likely source, but you will only know when you find it! :-)

Once you have found it, then you need to get it fixed...  depending on what it is, I have additional experience in resolving a number of these situations for myself and others - so happy to help as I can.

Stu K6TU

N7AIG

I'm a bit puzzled by the apparent quantization shown in the signal across the band. It looks like you are operating at the lowest limits of the ADC?

DV

If you pulled the antenna off the radio and the noise goes away then it's not likely to be internal to the Flex. I have had this problem numerous times during my time as a ham op and it if it is continuous, it always turns out to be a power line problem.  A few months ago I called our local utility about the same problem you have mostly on all bands. I turned my beam and peaked up the azimuth of noise source. The utility guys came out with some pretty basic equipment and their antenna pointed in the same direction.  They walked down the hill and found that an insulator had cracked and they corrected the problem on the spot.  If the noise can be heard on the lower HF frequencies, such as, in your case on 40 meters, you can do the same thing as the utility guys by using a transistor radio tuned to the high AM broadcast band.  Walk the poles until the noise blasts out at you.

Another thing to watch is an electronic filter on your furnace.  Mine had to be disconnected as it was adding a couple of S units to the noise floor 

Good hunting.

Mickey N4MB

Unfortunately, there are a lot of things it COULD be. If you have turned off everything, powered your radio from a quiet noise source (a battery?) and it persists, the next step is to DF it using a loop antenna and a portable radio.

If you can hear this on the broadcast AM band - I'll bet you can - you might be able to walk around the neighborhood and locate the general area of the noise.

If you believe that it is a power line noise, call your local power company, tell them that you are an amateur radio operator and that you believe that they're causing noise across a wide swath of the Hf Bands. Ask that they send out an RFI investigator.

If it is outside your house, it could be a number of things:

- Failed lightning arrestor on the power line (Large SCR) 
- Bad GFCI breaker.
- Someone's electric fence charger
- Invisible fence
- Ballast for halogen or flourescent lignts - anyone growing anything inside?

Locate your local ARRL Technical Specialist for interference help. 

73,

Mickey N4MB
ARRL Technical Specialist

Kevin LaFata

Thanks for the great responses.  I didn't even think to try to look at the audio waveform.  It definitely does appear to be 8-9 ms between peeks (that's as far down as I could go in resolution). But the distance between 10 of them was 83ms.

I'm headed out to find some stuff to make a inexpensive yagi. Lots of wooded area and hills around here so I think I'm going to try some DF.

And yes it can be heard on AM radio.

Mark Griffin

All you need is an AM Radio. Tune it to about 1400 and walk up and down the street. If not if you tune your car radio to about 1400 and drive up and down the street, that would serve the same purpose. Here's a question, when it rains does the interference decrease? And, if it is windy, does it increase? If that happens it is probably a local pole. You will need to call your power company and file a complaint. Make sure and tell them that you are an amateur radio operator, with a FCC Federal License. That will help, because they don't want you complaining about them to the FCC. They can avoid you, but not the FCC. Mark KB3Z

Stu Phillips - K6TU

Dead giveaway - its power line noise and probably a single pole within a mile or less of your house. 

When you find the pole on VHF, capture the audio again and compare it with the capture above.  If they are reasonable matches, you have the right pole.

Hopefully your power company is more responsive than Pacific Gas & Electric here in NorCal.  The only proven way to deal with PG&E is a direct letter to the CEO.  Their own internal process is to ignore all RTVI complaints and hope the ham will go away or go SK with old age.

Good luck and let us know what you find!
Stu K6TU

Kevin LaFata

Thanks for all of the great comments and suggestions!

Well..so far:

There are two power lines running along the common ground right next to our house. One is high voltage and goes directly to a coal plant. The other is a residential line that feeds underground wiring to the houses in the neighborhood. The are parallel and about 20 yards apart.

I have an Eton shortwave receiver I picked up years ago. On 1400 AM I walked around the immediate vicinity and the worst noise was actually right at the outside of my house. The noise was quieter when I walked towards and under the power lines.  The radio has a whip antenna and a "DX/Local switch" which I assume is an attenuator. That helped localize the noise a little.

The receiver also has an antenna jack. I finally completed a "tape measure yagi" and tried wiring that in. But since it's more for 2M, I didn't really get much from that. (But hey, there's a Fox Hunt next weekend and I've been meaning to complete that project).

I only have a FM (only) transceiver for 2M, I'm assuming that really won't help, even with a directional antenna.

It's suppose to rain later, which may give me another clue.

Other than that, I'm not really sure what to try next. Maybe wait until it gets dark and maybe I can find some arcing on one of the nearby poles ?



 

George KF2T

Since it seems strong close to your house - go with the battery radio and turn off your house...completely. Each individual breaker and the main. If the noise is gone, it's in your house. If not, well, it's not ;-) But it's possibly in the drop from the pole to your house, then.

I had an odd intermittent noise that bugged me for a while. Turns out there was a loose connection on the outside circuit breaker box. Why in Las Vegas they'd put them outside, on the south-facing wall, is beyond me. Talk about thermal stress. After cutting the mains completely, tightening up the connections and checking for corrosion cleaned up that particular noise.

Steve N4LQ

Why all of these speculations if you are not receiving it on another receiver as you stated (I think). 

I quote:
"I've used an RTL dongle on the laptop (with 125Mhz up converter) with same antennas but don't see the noise "

So if you don't hear it on your dongle then why bother to look elsewhere? Obviously something is wrong with your Flex or the power supply you're using. 

Take your Flex somewhere else, a friend's QTH or someplace away from your house and try it.
Do you HEAR the noise?

Kevin LaFata

Steve,  thanks for the suggestion.  Actually I did take the Flex out a couple days ago and operated remotely (about 3 miles from home).  No noise there. Back in the original post, I added that I could not explain why I didn't see the noise on the RTL dongle. Maybe the Flex has more sensitivity ?  Or maybe there's some filtering going on in the RTL or HDR# I didn't know about.

I will note that with the noise blanker on (on the Flex), I can hear strong signals fairly clear, so kudos there.

Stu Phillips - K6TU

Kevin,

If the noise is not close by AND/OR you don't use a yagi antenna on the RTL dongle, I'm not surprised you can't hear the noise at VHF.  Typically you need to be close - like 50-100 feet to start getting the noise picked up at VHF - you will need either an AM or SSB receiver to do this.  An FT817 makes a great RFI radio and is an order of magnitude cheaper even when new than the professional RFI receivers from Radar Engineering.

George's advice is a good start - I would definitely start there.

If the noise doesn't go away when you **** power to the entire house you know you have to look close by.

Unless its a really bad arc, you won't see anything at night.  Often the arc is tiny and can be hidden from sight by the pole, hardware on the pole etc.  Many times the issue on the pole is a loose bolt on a non-grounded part of the pole (itself a safety hazard to the line men working on the pole...) or is the wire used to cross tie the power line conductor to the insulators atop the pole.

If you can find the pole including on VHF, then report it to the utility company and they will take it from there.

Stu K6TU

Jason Whiteaker

What's odd is that the noise is so broadbanded, and at a -80 db or stronger signal. However, your S-meter never goes above S5? The other RX doesn't see it. It makes me wonder if you've got something going on local with the radio, the LAN, power supplies, ground loop, and/or something else in your shack.

That noise doesn't look like power line noise at all. Power line noise has a definite peak at 120 Hz, plus even harmonics.

Again, this looks unique to the immediate environment.

Good luck! I know how annoying it is to track interference!

-Jason, NK9B

Joe, KQ1Q

Kevin, I can't see any pattern on the waterfall in your video. It's important to characterize the RFI by frequency at various resolutions -- how broad, how many bands, are they drifting in frequency or stable, etc. You can usually just take screen caps of it. See the ones I previously posted (which I'm still investigating): http://joema.smugmug.com/Hobbies/Ham-Radio2/RFI-163-Heathersett-Drive/48523970_ZBr6HG

As already stated, it's a good idea to run the Flex off a battery and laptop and pull the main breaker to your house. Also shut down all UPS units. 

In my case I'm waiting to receive this HF Direction Finder: http://www.nationalrf.com/noise_location.htm

See also Stu's excellent blog on RFI hunting:
Parts I through VII: http://1vc.typepad.com/ethergeist/2010/02/rfi-hunters.html
Parts VII and VIII: http://1vc.typepad.com/ethergeist/2010/04/rf-hunters-vii-we-close-in.html

Kevin LaFata

Just as suddenly as it started, the noise stopped sometime overnight. I pulled up a close by weather station via aprs.fi and it showed we received 0.03" of rain a couple of hours ago. My "auto-screen-shot" software stopped working so I didn't capture exactly when the noise stopped though

I've appreciated everyone's help, you all have given great suggestions. I'll keep this thread bookmarked for when the noise inevitably starts back up again ...

Joe, KQ1Q

Re screen shot software, you can just do Shift-Print Screen (hold down shift key, hit print screen button) which puts the screen contents in the clipboard. Then you paste it into any graphical program such as Windows Paint, Photoshop, etc, and save as a .jpg.

Part of solving these cases is tracking their behavior over time. IOW what time of day, what day of week, does wet weather affect it, does hot vs cold weather affect it, etc.

Kevin LaFata

Joe,

I always like to make things more complicated than they need to be      I was using a program called "Snag It" on a different computer, had remote desktop set to the PC connected to the Flex, and had it set to take screenshots every 20 minutes. That way I could look and at least maybe find one waterfall where the noise stopped.

Of course, yesterday I tried more testing with the circuit breakers turned off, and I forgot to reset the automatic screen shots..  That's probably what "caused" the noise to fix itself. It knew I wasn't watching at the time.

Stan VA7NF

Kevin, your panadapter display is very interesting as most noise investigations are with a baseline + noise that follows a frequency based pattern.  Yours is reversed with a S5 "steady state" with both frequency and time based removal of noise.  I have trouble keeping my mind reminded that I am looking at a frequency based not a scope time based display.

This strikes me as something similar to a bad coax connection where something like power line induced voltage is being rectified/mixed with other signals then intermittently grounded (the ground connection may also be involved).  The case I recall gave me BC band images (base + noise/images) but if the main source in this case is a 60Hz strong signal induced and rectified from the HV power lines then the mixing products may produce a high flat-line base. 

Techniques offered here are all solid EMI chasing suggestions.  Probably will restart as things dry out or you heat things up with high power RF.

73, Stan - VA7NF

Kevin LaFata

Here's a better screenshot.. I'm not sure why there were so many jumpy lines in one particular zoom level in the earlier video. This is a bit closer.  And the noise is back today. So looking on the bright side it gives me a better chance at tracking it down

Stan VA7NF

Such a different display - Note the horizontal pattern in the waterfall, repeating around 1 per second.

Jump in the car and head towards the coal plant and expect to find something like a variable speed conveyor belt or pump (VFD-Variable Frequency Drive).  Also expect a strange look when the geek arrives with a radio and DF antenna.

Stu Phillips - K6TU

Kevin,

This very much looks like powerline RFI.  Check the audio signature again and if it has the same 8.33 ms signature, its powerline generated.  

I have a very similar situation with a pole about a quarter of mile from me that I'm waiting for PGE to fix... I tracked the pole down and verified it as the source by DFing the noise first at HF, then at VHF.

I see the same patterning on the waterfall.

From the signal strength, I'd say the source is very close to you.
Stu K6TU

Stu Phillips - K6TU

Stan,

The signature of this is very different from a variable speed motor controller - you can see the waterfall from one such source here:

http://1vc.typepad.com/ethergeist/2010/02/rfi-hunters-vi-the-signature.html

VSC have a repeating pattern spectrally based on their switching rate - the RFI gets back fed into the power distribution system and radiated.

If you look higher up this thread, you will see the Audacity trace of the interference that Kevin reported - the signature is a very good indication its power line generated noise.

Stu K6TU

Stan VA7NF

I will probably stand corrected on this item but some of the VFDs, especially my own, have the repeating patterns overlap and loose their definition up at 20M while having distinct patterns on 160M.  I was particularly relating the coal plant, high voltage lines, and clear repeating time pattern.

Thanks for the correction. 

Stu Phillips - K6TU

Not a correction - just sharing information. Thanks for the comment about the pattern disappearing. That's good to know as in my case, the VSC interference eventually became much weaker and disappeared into the noise floor.

I looked at Kevin's QTH on QRZ.com and he has both a main power line as well as local distribution poles right next to his house. Hope he can find and get the culprit fixed!

Stu K6TU

Kevin LaFata

Update: I have not been able to build any type of directional antenna combined with my limited equipment to track down the exact power pole. I know it has to be close (there's only three possibilities) though.  The only VHF equipment that does AM (or anything besides FM for that matter) is the USB dongle connected via Laptop. Not very portable while holding a yagi.  Can't say I didn't try though. But I could not get any bearings on the noise.

I did put a call out to the power company thought. I was friendly, told them what I tried, mentioned I cannot listen to broadcast AM stations, as well as not being to operation amateur radio. They sent someone out in less than an hour.  They apparently found some issue, and will schedule some work in the future.  I'll call in a day or two and see if I can get a timeframe though.

I'm disappointed I was not able to "find it myself", but I'm still new and learning. I now have two yagis for this weekend's foxhunt though.

k3Tim

It;s good the power co stepped up to the plate so quickly.  I believe fixing some these problems saves them lost power (arcing to ground) and possible failure in the near future.
Hope this clears up your RFI...

Best,
Tim

Kevin LaFata

34 day follow up:   I received a phone call from a lineman (while I was away from home, of course). He said he was at a power pole near my house and tightened up some connections. Since it had rained recently there was no way to test for sure.  His voice mail was very nice, he seemed friendly, and so far today, on a sunny/windy day, no RFI.   So, even though it wasn't an immediate fix, I think I am back to being able to operate on non-rainy days again.