Tag Archives: How to filter noise from shortwave

Steve tracks down the source of persistent radio interference and gets it addressed

Photo via Unsplash

Many thanks to SWLing Post contributor, Steve Allen (KZ4TN), who shares the following guest post:


Tracking Down Radio Frequency Interference

by Steve Allen, KZ4TN

I first noticed the RFI in late November 2019 as a steady buzz at around S9. It was present over most of the high frequency spectrum. I waited until the second week of December to see if you would end on its own, no such luck. I put an HF rig in my truck and started driving around the area to see if I could find a potential source. About a quarter mile from my home is a 161 KVA substation operated jointly by the Tennessee Valley Authority and my local electrical utility. When I parked in the driveway outside of the gated substation the sound of the interference was very strong and blanked the HF spectrum. I called the phone number on the gate and after an explanation of why I was calling I was connected to a fellow radio operator. I explained the situation and he said he would bring the issue to someone’s attention and get back to me.

A week went by and I didn’t hear back from the TVA. I called the person I spoke with previously and he said that the individuals that he spoke with questioned the validity of my findings. He was very helpful but said he didn’t have much clout with the TVA, RFI investigations were not his area of responsibility. I told him I would be happy to meet with someone from the TVA and show them what I had found. I also said I would contact my local electric utility and see if they had an RFI detector so we could eliminate their equipment. My initial contact at the TVA said he would keep trying to get someone to take this issue on and work with me to investigate. I said I would call him back next week.

I then called the local utility company and talked to someone there who was familiar with these kinds of issues. The local utility company owns the output side of the equipment at the substation. He told me he was going to perform an infrared (heat) inspection of their equipment at the substation mid January as part of their annual maintenance and will also check the low voltage utility lines near the substation. I told him that I didn’t notice this RFI until after they had a power outage nearby. He said he would try and get over earlier and check the power lines that run along the streets and look into the power outage history for this area.

All during this time I kept a daily log of the RFI including time of day, frequency effected and S unit level. I also logged the weather conditions. To eliminate the electronics in my house as a possible source I connected my transceiver to a 12 VDC battery and shut off the mains circuit breaker, the RFI did not change at all. I also visited the ARRL webpage that provide information on RFI including recordings of known RFI:

http://www.arrl.org/radio-frequency-interference-rfi

The ARRL is the best source I have found in finding and fixing RFI.

By December 27th,  no word back from anyone. I assumed that they were off for Christmas but decided to write a letter to the TVA as a follow up to what had happened so far. In early January I received and email from one of the TVA engineers who said he would contact a field engineer who would contact me. The next day I received an email from the field engineer who said he was going to be in the area on another job but would meet me at the substation.

So, of course as soon as I am making headway with finding the problem the RFI diminished to the point of not being a problem. By this time here in Northeast Tennessee the winter temps are in the 40s and the humidity is lower. For whatever reason, the RFI ended. I met with the field engineer and we agreed that if there is no RFI there is nothing to search for.

Fast forward to August, 2020. In June and July I had been operating digital, mostly FT8. I usually had the volume control at zero and as it was summer I was doing no shortwave listening. One day I decided to tune around the bands and found that the RFI was back as strong as it was during December at S4-S9 from 2-30 MHz. I emailed the principal engineer I had previously been in contact with at the TVA and he told me he would contact another field engineer and that he would come to my house with an RFI locator and start a thorough investigation. The next day I received an email from the field engineer and we scheduled a time for him come over.

Upon his arrival he connected his RFI locator to my vertical antenna and tuned across the spectrum. The locator immediately displayed the signal. He captured an electronic image and said that he could now drive around the area and try and find a match. A hour and a half later he called and said he was unsuccessful and wanted to come back  and make sure the signal was still present. Sure enough, it still displayed on his locator and he was puzzled why he could not find a similar signal while driving the area. He said he would send a copy of the recording to the TVA engineer and get back to me.

A few days later I heard back from him and he wanted to come over again and make another recording. I believe after discussing this issue with his supervisor he was going to use a different method of searching the area. After a couple of hours I received a phone call from the field engineer telling me that he thought he had found the source of interference. Using a parabolic antenna he had found two different utility poles that appeared to have defective lightening arrestors on them. Both are within a quarter mile of my QTH. These poles are the responsibility of the local electrical utility not the TVA. He said he would contact them and follow up with me in a few days.

In a couple of days the interference was very low to nonexistent. Shortly thereafter the engineer contacted me saying the local utility company had completed the repairs and wanted to know if the interference was still present. I said I hadn’t hear it in a couple of days and I would get back to him if it returned. A couple of weeks later I received an email from the field engineer detailing the incident, what he had done to locate the interference, and what was done to repair it. In his email he stated the service was provided at no cost by the TVA Right of Way and Elizabethton Electric Department through TVA’s Comprehensive Services Program (CSP). I am so appreciative of the Tennessee Valley Authority. The airwaves are now free of manmade interference and I am looking forward to another winter of operating and listening to shortwave radio. Here in the 21st century there are so many electronic devices that are capable of causing RFI. I am very thankful that my station is RFI free (for the time being).

Steve Allen, KZ4TN
Elizabethton, TN


Thank you so much for sharing your story, Steve. Only recently, we posted Emilio’s article about tracing interference to poorly made switching power supplies. Thank you for sharing how you approached your local utility company, in your case, to resolve your RFI!

Very encouraging! Readers note that you don’t always have to live with persistent RFI. If you know the source isn’t coming from within your home, sometimes it’s simply a matter of getting your local utilities company to investigate.

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Post-storm power outage leads Emilio to find the RFI-spewing source of his problems

Storm with lighteningMany thanks to SWling Post contributor, Emilio Ruiz, who shares the following guest post:


Apprehending an RFI-generating monster!

At the beginning of the year, I was sad because, at home, an awful RFI noise appeared. The next few months the noise increase until S9!!. Day and night my receivers and my feelings were so dampened with this terrific RFI–only the lower Broadcast Band (900 to 540 Khz) was relatively immune to it.

Yesterday, we had a storm and the mains electricity service went off, so I connect a 12 volt battery to my RT-749b military surplus transceiver and the received signals were very clean like the “good old days”.

(Above: Listen W1AW loong distant from my QTH in Chiapas Mexico).

When the power electricity come back on, so did the RFI too!!

(Above: W1AW gone)

Remembering the recently publish post in SWLing Post about RFI, I did some testing by
cutting the electricity to my home (the main switch) and the RFI was gone!! So I discovered the RFI lives in my house–not in the outside wires!!

I put batteries in my old shortwave portable radio and searched (like Ghostbusters) all outlets contacts, one by one, connect and disconnected each device.

And I found the guilty party!

Exhibit A: The Mitzu laptop power supply

On December 2019, the power supply of my son’s laptop broke, so I bought a cheap substitute.

The RFI produced by this little monster could be heard at a distance of about 200 meters from my QTH!!! (Much like an old transmitter spark gap–!)

Even this cheap power supply apparently featured ferrite toroids on the wire but turns out it is fake!! It was only a plastic ball!

Exhibit B: Fake toroids!

The wires were also not shielded. No doubt one of the worst switched-mode power supplies I could have purchased.

Exhibit C: The Mitzu RFI generator wire without shield, only pair wires!

I found a old Acer power supply with same specs and I replaced out the RFI monster one.

And now? The shortwave bands are clean again.

(Video: Testing my Kenwood R-600 rx with Radio Exterior de España… plugging and unplug the Mitzu monster RFI generator).

So I wanted to share what happened to me, so perhaps it can be useful for other SWLing Post blog friends.

Watch these little switched mode power supplies from all devices in your home. Replace them if you detect RFI levels that harms SWLing. Consider disconnect all devices (vampire consumption–or phantom loads) if not in use; the radio waves and electric bill will be grateful to you!


WOW! What a difference! Emilio, that was great investigative work on your part. It’s as if that switching power supply was specifically designed to create RFI! No shield and fake toroids? That’s just criminal in my world! 

Thank you so much for sharing your story. Hopefully, this might encourage others to investigate and apprehend their own local RFI monsters!

(And by the way, Emilio, I love that RT-749b military transceiver!)

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Running SoniqWare SG-1 on a Windows PC

sg1-gui-fordocRecently, I posted a video showing how @LondonShortwave uses the GarageBand plugin, SoniqWare SG-1, for noise reduction. Since GarageBand is an Apple application, I didn’t believe SoniqWare SG-1 would work on a Windows PC, but SWLing Post reader Jeff Benedict (KB7AIL) writes:

“I run Mac OSX and GarageBand so it’s not really a concern of mine but, according to the documentation, SG-1 is compatible with Windows sound processing applications.
Here’s the documentation from SoniqWare:

From:  http://www.soniqware.com/pdf/SoniqWare-SG-1.pdf
p. 17

System Requirements
• Microsoft Windows XP/Vista,
• Mac OS X 10.5/10.6,
• 512 MB RAM,
• VST, VST3, or AU compatible host software

An explanation of the VST and a list of applications for Windows which are compatable with VST plug-ins:

http://en.wikipedia.org/wiki/Virtual_Studio_Technology

Of course, this comes with the caveat that I do not run any version of Windows or any of these sound processing applications so YMMV.

A short explanation of the different formats for sound processing plug-ins:

http://support.pluginboutique.com/knowledgebase/articles/51119-interface-types-explained-vst-rtas-au-etc-

Many thanks, Jeff, for the tip!

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Shortwave noise reduction via GarageBand plugin

sg1-gui-fordocMany thanks to @LondonShortwave, on Twitter, who made a video showing how to use a GarageBand plugin to filter noise out of shortwave audio in real time. He describes this on his YouTube channel:

“I recently discovered a Mac AudioUnit plugin called Soniqware SG-1 that allows real-time noise filtering based on a brief noise sample (sometimes referred to as the “noise profile” or the “noise fingerprint”). This video shows it being applied to shortwave radio signals, which I believe is a first, as I have been unable to find anyone else who has already done it. In a number of cases, it turns laborious DXing into armchair listening.

The antenna used in these experiments is a Wellbrook ALA1530SP-1 and is positioned indoors. More information is contained in the first few seconds of the video.”

Click here to watch the video on YouTube.

Note that GarageBand is an application only available on the Mac OS X platform. Fortunately, it comes free with every new Apple computer purchase. You can find the Soniqware SG-1 spectral noise gate plugin by clicking here.

Be sure to follow @LondonShortwave on Twitter: http://twitter.com/LondonShortwave

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