How to find RF noise culprit

[7designs]

Since I bought and moved into this house I have had so much problems with RF noise. At first I didn't know it was noise, thought it was bad signals since my house is surrounded with trees. Then I thought it was the big power lines that run by the house.

Playing around trying to listen to some am broadcast I noticed horrible RF interference which peaked at 750 khz. I grabbed my Grundig G6 tuned to 750 khz and walked outside. As I walk away from the house the noise goes away and WSB in Atlanta, GA comes in very clean. I can walk around the entire house and the noise is gone until I walk closer to the house.

This rules out the power lines. The noise is there even when I use my long wire antenna's 30ft in the air attached to my tower(next to the house) and coax grounded at antenna and base of tower.

I have also noticed a weird issue if a television cable is unplugged in the house my home theater sub will hum, picking up RF through the RCAs.

My plan tomorrow is to flip the main breaker in the box and see if the noise goes away, if it does I will turn back on one breaker at a time till it comes back, then trace down the circuits on that breaker till I find the culprit. If turning the main breaker off does not eliminate the noise I am not sure where to check next.

Sorry for the long post but was curious if anyone had any advice for tracking down the source of the RF noise? I would try to use the radio, but as soon as I am in the house the noise has maxed out the radio.

Thanks

 

[KC4RAF]

Hope this helps you some.

That’s a good analytical way to find or solve the problem RFI. If you can determine the circuit at fault, but you have too many motors, electronics, or other appliances on that line, you’ll need to unplug them one at a time to further eliminate the cause. Also, double check after you unplug or turn off a breaker that there aren’t other sources of RFI. Does you house electrical system have a good grounding circuit? Check the ground rod connections (or pipe if so connected). Usually you can grab the bare ground wire and wiggle it around a bit to see if it’s loose.
I’m sure you’ve got your job cut out for you, and I doubt that I need to say “Be CAREFULE”! Keep us posted on your progress and if you eliminated the problem and if so what was at fault. And if necessary ask for some help if needed.
You really need a good clean RF surrounding without any interfering RFI for your new Hallicrafters S-20R Sky Champion !

Also, you may try using your scanner without the antenna for further investigating the RFI. There will be others coming online with more helpful hints and info for you to check and locate.

 

[SCPD]

Do you have DSL?

 

[kruser]

Turning the breaker off and then back on a circuit at a time is a good method as long as the noise does stop when you kill the main.
I've also reduced the sensitivity of my "sniffer" radio (your G6) by turning on any attenuators. I ended up using an old and small transistor radio.
I'm in an apartment so I did not have good results. It all depended on what the neighbirs had plugged in.
Plasma TV's are known as a very bad noise source. My number one killer was afaulty dimmer in one of those pole or torcier lamps. It was one of the old quartz type that they outlawed due to fires from the lamps extrmeme heat.
It was in a neighbors apartment and was wiping out radio + my DSL connection. In this case, the lamp was located just inside the wall that all the power meters and main disconnects were located. So it was inducing its signal on the electrical wiring throughout the building. I was lucky and found it by using the AM radio. Then the neighbor was a nice kid whose DSL was also having issues but he never matched his DSL issues with when he turned that lamp on! He let me replace the dimmer with a fixed on/off switch as he said he always ran it full out anyway. Problem solved.
Then a had a bad case of noise again with the stronger signals in the AM broadcast range and I tracked that to something riding on the shield of the incoming cable tv coax. I thought I was screwed but a call to the cable co brought them out and they checked and cleaned all grounds in the amp cabinets mounted around the building. That helped but not fully. I still had a high noise floor. One day, it stopped so I suspect it was something noisy in a neighbors apartment that was riding along the coax as common mode noise.
In between that, I purchased a magnetic loop antenna and that cured all my noise problems.
I still like to use my longwires from time to time though so one day I come home to yet another noise source that was loud all over the bands.
I tracked that noise to be riding on the shield of another neighbors coax cables that fed to him from his directv dish on the roof. My longwire passed right over his coax at right angles. I moved my longwires to the other side of the large roof and that helped a ton. I later became freinds with that neighbor and he did the unplug the sat receiver test for me and the noise did stop. He let me try all kinds of filters but nothing I tried would fully stop the noise. His dish was also located very near my scanner antennas and the new loop so I moved the entire dish to the furthest corner of the roof away from my antennas and that also cured most of that noise. I'd also tried grounding his receiver at the inside end but that did nothing at all. Same for grounding the dish coax at the dish end, no help.
Most of the noise I find seems to ride on the AC power wires or the shields of coax and it is almost always what it called common mode noise. It can be hard to stop.
Then I have a decent size power sub-station that is only maybe 200 yards from me. That thing is noisy but only when they switch loads around. Sometimes they will get a bad insulator that is arcing or a loose connection on the pole but the power co is very good at responding to and fixing RF noise complaints. The guy that does their noise issues gave me his cell number and told me to call him directly so he can get here quick as a lot of that noise comes and goes with the wind or even the humidity. It will start up when the humidity dries out during the day and then it goes away again at night when the humidity rises.
This guy has all kinds of things for finding it but he usually uses an ultrasonic receiver with a small parabolic dish that he listens for the noise when he gets close.

With any luck, your noise will stop when you kill your main and then only start back with a single breaker. Then just figure out what that breaker runs and start unplugging things on the circuit. As you turn the breakers back on, give each one some time for equipment to start back up or become warm. I had one that took several minutes before the noise would start so I did my test in reverse by listening as I turned each breaker off. As soon as I hit the correct breaker, the noise stopped.
Suspect items can be anything but watch for lamps/lights that are on dimmers, motion activated outdoor ligthing, many of the newer lamps can also cause noise. Both the CFL and LED types as well as some flourescent fixtures as most use electronic ballasts these days.
I've also found some cheap no name made in China computer power supplies that put out harmonics or noise on a wide range of frequencies in the HF and lower bands.

Your breaker switching idea is a very good starting point though and hopefully killing the main will stop your noise so you then know you have control of the noise and can usually find and cure it.
I don't have that luxury as I think I'd piss off a lot of people if I killed the main power coming into the apartment complex!
Sometimes it can be hard to fix or even find but give your breaker killing test a try and see what happens.

As rafdav said, please post back with your findings and good luck!

 

[7designs]

FOUND IT!

Flipped the main breaker noise stopped s0 noise floor. Turned power back on and still s0 telling me it was something running that did not start back up when power came back on. Well that made me suspect my PCs. Turned my computer on and instantly s9.

So I have to PCs in the home and both cause s9 noise. But my laptops and other electronics do not cause the noise. Cable modem and wrt54g router cause no noise.

With my desktop computers off I have never seen it so quite. Many am stations coming in as I write this. Even the issue with my home theater powered sub is gone!

So, now how do I get the noise out of the PCs?

I am going to try grounding the chassis to a ground rod and see if that works. But at least I can shut them off when I want to use the radios. Thanks to all who have replied.

 

[kruser]

Do you have DSL?

DSL does not normally cause or emit noise but it sure can be affected by noise in the MW band as that is where it operates. Noise in that band can totally wipe out a DSL signal.
Now the switching type power supply wall warts that come with almost everything these days are another story. Those things can be very noisy no matter what they are powering (DSL modems, routers, radios etc.).
The OP's breaker test should find that instantly though.

If you do find that a DSL signal is radiating from a phone wire, I'd first look at the phone wire and make sure it is at least Cat3 UTP or better and not the old untwisted pair stuff that most older homes were wired with. Still, the signal levels from a typical DSL modem are very low and should go unheard after moving any receiver antenna just a few feet away from the phone cable. The original DSL operated from around 60 kHz (or maybe it is 30 kHz) up to 1104 kHz so it definitely falls in the AM broadcast range. Then the newer DSL such as vdsl which Uverse uses, runs even higher in frequency. I have three DSL lines here all fed from a CO building that is far away so my modems all run at the maximum power level allowed and I've never had any noise worth mentioning radiate off the phone lines.
I'm sure if I placed a sensitive receivers antenna right alongside my phone cables that I would hear or see the noise floor rise though being a dsl signal is pretty widebanded!
I have tested my phone wiring and the DSL signal riding on it before. I went down to the ground floor and unplugged my lines from the NID so the signal was not making it up to my 3rd floor apartment but I never found any noise that bothered my receivers.

 

[kruser]

FOUND IT!

Flipped the main breaker noise stopped s0 noise floor. Turned power back on and still s0 telling me it was something running that did not start back up when power came back on. Well that made me suspect my PCs. Turned my computer on and instantly s9.

So I have to PCs in the home and both cause s9 noise. But my laptops and other electronics do not cause the noise. Cable modem and wrt54g router cause no noise.

With my desktop computers off I have never seen it so quite. Many am stations coming in as I write this. Even the issue with my home theater powered sub is gone!

So, now how do I get the noise out of the PCs?

I am going to try grounding the chassis to a ground rod and see if that works. But at least I can shut them off when I want to use the radios. Thanks to all who have replied.

Good deal!

Are they home built computers? I'd see if you can borrow a power supply if they use standard ATX type supplies and start by swapping out the power supply one at a time.

Also, unplug all cables leading out of the computer including keyboards and mice and any USB devices and see if the noise is coming from an external device. I've seen some very noisy keyboards before.
I have also had some luck by grounding the chassis such as you are going to try.
Then I've had some computers that I could not shut up no matter what so I replaced them if they were something I needed to leave riunning while working with the radios.
Most times though, I was able to replace the power supplies and that would almost always cure the noise for me.

edit: I also found a lot of noise from my network cabling. It grew way worse when I switched to a 48 port gigabit switch and everything started running at gigabit speeds. I ended up buying a spool of shielded Cat6 cable and made up all new long runs and then bought shielded short cables and that cured the network noise. For me, my network noise seemed to mess with VHF low band (30 to 50 MHz) more than anything but I'm sure it could also mess with MW frequencies.
I also make sure all my computer cases are solid steel and not the kind they sell with plastic windows so you can see inside. Those cases offer basically no RF radiation protection as everything just comes right through the plastic window. It is about the same as hooking up a motherboard with all its cards and setting it on a desk with no case around it at all. You'd be amazed by all the stray RF floating around in a computer!

 

[7designs]

Luckily I can shut them off when I want to use the radios.

 

[kruser]

Luckily I can shut them off when I want to use the radios.

That is exactly what I do when I'm going to do some serious monitoring!
I kill almost everything not needed for the radios actually. Even my UPS units emit some garbage and it all seems to be cumulative in nature so with enough stuff still plugged in, my noise floor would be rather high.
The loop antenna did help big time in that area though.
If you find more noise, look around for wall wart power supplies as many are switchers and ru very noisy.
My Icom R75 came with a switching power supply. I found a note inside the owners manual from Icom stating that the power supply may cause unwanted noise! Mine did not mess with anything I monitored so I used it for a while until I was able to move the R75 to my large battery supplied power circuit. I have huge SLA batteries that can deliver tons of amps at 12 VDC for everything I have that can run from 12 volts. I operate from those batteries when working with weak signals which is a lot at night for me.
Run that way and also kill my computers and it is pretty quiet around here.
I have one computer that I consider my main computer. I took special precautions when I built that one. I ran braided ground straps all over inside and outside the chassis plus played around with things like the video card and selected one that was rf quiet. That computer is almost noise free and I will run it when I do digital signal decoding. I also have one laptop that I've not found any bad noise from that I use when operating in the dark as I call it.

 

[SCPD]

FOUND IT!

Flipped the main breaker noise stopped s0 noise floor. Turned power back on and still s0 telling me it was something running that did not start back up when power came back on. Well that made me suspect my PCs. Turned my computer on and instantly s9.

So I have to PCs in the home and both cause s9 noise. But my laptops and other electronics do not cause the noise. Cable modem and wrt54g router cause no noise.

With my desktop computers off I have never seen it so quite. Many am stations coming in as I write this. Even the issue with my home theater powered sub is gone!

So, now how do I get the noise out of the PCs?

I am going to try grounding the chassis to a ground rod and see if that works. But at least I can shut them off when I want to use the radios. Thanks to all who have replied.

FYI, the WRT54G router does cause noise but at VHF and within about 3ft.

I recently upgraded to the Cisco 2700 router and it has zero noise on HF or VHF.

Very likely your power supply is the culprit. The cheaper units do not have much in the way of RF filtering. I use a Corsair power supply and it does not emit any RFI.

And I leave my computer on full-time since my primary radio is a SDR.

PS. This is a must read for PC builders: http://www.hardwaresecrets.com/article/327

 

[k9rzz]

A number of years ago, I had a desktop computer that was very RF noisy. Always one to grab a soldering iron whenever I got the chance, I put 0.01mf ceramic caps to ground on every wire that exited the power supply. (not that hard of a job).

Noise GONE.

 

[7designs]

Shutting off the computer allows me to use a home receiver with a 45ft long wire to pull on AM Clear Channels over 1000 miles away. Much better then not even being able to tune in my local clear channel.

Now we can keep working on getting further out.

 

[7designs]

Switched over to shortwave with the Grundig G6 same antenna as above. Quickly tuned in BBC on 6195. Then on 9750.

Wow, never seen so many shortwave stations come in on this little radio! This is going to be amazing when I get that Sky Champion in!

 

[Viking1]

FOUND IT!



So, now how do I get the noise out of the PCs?

I am going to try grounding the chassis to a ground rod and see if that works. But at least I can shut them off when I want to use the radios. Thanks to all who have replied.

That usually solves it, also place RF chokes around the cables at the back of the PC and monitor, The noise can actually use the cables as transmission antennas. Also a large choke covering all the wires exiting the supply on the inside can help.