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Radio Frequency Interference (RFI)

ARRL's Role in RFI Investigations

ARRL helps amateur radio operators through both technical and process hurdles often experienced while investigating RFI to or from a ham’s station.  Most assistance, well over ninety-five percent of assistance from the ARRL, is due to interference to an amateur radio station.  There are very few instances where ARRL is called upon for assistance, and the radio amateur is causing the RFI.

So how does ARRL help with RFI investigation?  First, ARRL provides technical assistance in finding the source of the RFI, whether its coming from a device in the amateur radio operator’s own home, a neighbor’s home or power lines, ARRL can help by working with ham’s to identify the RFI through the characteristics of the noise source, helping with Direction Finding (DF’ing) techniques and in advising ham’s on how to approach their neighbors when the noise appears to be coming from a neighboring home. 

ARRL can also help with process issues. For example, ARRL can help with interpreting FCC rules & regulations, and under ARRL’s cooperative agreement with FCC, ARRL can often document RFI problems on behalf of amateur radio operators through the transmittal of a letter to the individual or corporation responsible for the operation of the RFI source.  If ARRL’s efforts do not yield sufficient results, ARRL can work to bring about a resolution through FCC involvement.  In most cases, RFI issues are resolved even before ARRL writes a letter to the individual or corporation causing the RFI.  Further, there are very few cases that need to have formal FCC involvement to bring about a resolution. 

Investigating RFI Issues

In the course of investigating RFI issues, two questions are frequently asked of us at the ARRL lab.  The first is generally “what does this RFI sound like to you?” And the second, “what does this RFI look like to you?”

Aside from a few very distinctive types of RFI (for example, power line noise), it is difficult to identify what specific device is causing interference based on the sound it produces, or the visual signature in a waterfall.  In fact, the most useful question to ask first regarding interference isn’t necessarily “what is producing this interference?” but “where is this interference coming from?”

Once the source of RFI is determined to be coming from a specific location, the process of identifying the actual device causing issues can be less of a challenge.  Even knowing, without a doubt, that the source of RFI might be an LED light, its impractical to ask all of your neighbors if they have one of those lights.  They may not know the make/model of all their bulbs, and to make matters worse, the RFI might be coming from another neighbor's home.  While clues about what might be causing RFI are helpful, ARRL advises hams to prioritize and do their best to track down where the RFI is coming from, if that is practical and safe to do.

While some common causes of RFI might be power lines and devices in others' homes, many of the RFI cases that come through ARRL are found to be in the amateur’s own home. Never underestimate the power of simply taking a trip to your circuit breaker box and cycling cicuit breakers while listeninng with a portable radio to see if having a circuit off cures your RFI problem.  This can be the best first step when determining where your RFI might be coming from.  

In summary, you should follow this general process if you have an RFI issue at your station:

  • Keep a record of when the RFI started, what bands/modes you hear it on, and document the symptoms;
  • Focus on "where" the RFI might be coming from, rather than "what" the RFI might be;
  • Do some work on your own to ensure the RFI isn't coming from your home, such as the circuit breaker test described above;
  • If you can, perform some DF work on your own (or with a fellow ham) to try and locate the source of the RFI.  One simple test is "sniffing" with a portable radio to try and locate the source of the RFI.  Further reading can be found at the links below under articles;
  • If you contact a neighbor, a utility or other company regarding the RFI, it helps to keep a record of those conversations/contacts; and
  • If you are going to reach out to ARRL for help, we encourage you to make a recording of the RFI, generally 30 - 60 seconds in AM and SSB, this can be helpful in RFI investigations.  Programs such as Audacity can be a useful tool for examining the spectral characteristics of the RFI you are experiencing, and new tools such as Software Defined Radio (SDR) and integral spectrum scopes can also be helpful in analyzing potential noise sources.

Lastly, note that Dave Cole, NK7Z, an ARRL Technical Specialist, has a helpful flow chart for locating RFI on his web site.  And if you need some assistance from ARRL, feel free to contact our RFI Engineer.

Getting ARRL's Help

If you need ARRL's help in either investigating RFI from or to your station, we are just a phone call or an e-mail away.  You can call our RFI Desk at (860) 594-0392, or you can contact Stephen Anderson, our RFI Engineer, through e-mail at  To make the best use of our time, we also request that radio amateurs opening up an RFI case with ARRL complete one of the following two forms, as may be applicable to your particular RFI case:

Web Links

Naval Postgraduate School RFI Handbooks

Special thanks to George F. Munsch, W5VPQ for providing these documents.  They contain useful and comprehnsive information for both RFI locating and noise mitigation.  By Wilbur R. Vincent, W6PUX, George F. Munsch, W5VPQ, Richard W. Adler, K6RWA, and Andrew A. Parker, WV1B.



What Is It?  While this question may seem intuitive, it may be the wrong one to ask if you have an RFI problem.  By Ed Hare, W1RFI.

Electronic Noise Is Drowning Out the Internet of Things.  Our increasingly connected world needs better protection against RF noise pollution, By Mark A. McHenry, Dennis Roberson & Robert J. Matheson.  IEEE Spectrum, August 18, 2015

Hunting Down RF Noises.  Find noise sources both outside and inside your home with a systematic approach, by Michael Foerster, W0IH.  QST February 2015, p 45.

Locating RF Interference at HF.  A proven and practical approach to dealing with RFI from grow lights and more, by Tom Thompson, W0IVJ.  QST November 2014, p 33.

A Quick Look at Radio Frequency Interference, by Joel R. Hallas, W1ZR.  QST May 2009, p 61.

Interference Primer - Parts 1 and 2 Derived from QST Lab Notes columns.  Contains general information on Radio Frequency Interference.

RFI: ARRL Laboratory On Television--WATCH!

ARRL's Ed Hare, W1RFI and Mike Gruber, W1MG talk about RFI problems on a Common Point, a Cable Access TV show hosted by Dan Thomas.  Mr. Thomas serves on the Board of Directors of the Vintage Radio and Communications Museum of Connecticut (VRCMCT). Associate Producer: ARRL Assistant Laboratory Manager, Bob Allison, WB1GCM.

Identifying & Locating Power Line Noise, Produced by the ARRL Laboratory, written and directed by Bob Allison, WB1GCM and narrated by Jerry Ramie, KI6LGY

Power Line RFI Investigation in Pleasant Hill, California, Video of an RFI Investigation in Pleasant Hill, California.


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