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Radio Frequency Interference (RFI)


As our lives become filled with technology, the likelihood of electronic interference increases.  Every lamp dimmer, garage door opener or other new technical “toy” contributes to the electrical noise around us.  Many of these devices also “listen” to that growing noise and may react unpredictably to their electronic neighbors, including Amateur Radio transmitters.

Sooner or later, nearly every active Amateur Radio operator will have a problem with interference.  This could involve interference to a neighbor's equipment, or, more likely, some form of intererence to Amateur Radio from the noisy devices that can sometimes even be found in our own homes.  The good news is that most cases of interference can be cured!  The proper use of “diplomacy” skills to communicate with a neighbor and standard technical cures will usually solve the problem.

Asking “Where” Before “What”

A message from ARRL Laboratory RFI Engineer, Paul Cianciolo, W1VLF:

In the course of investigating interference (RFI) issues, two questions are frequently asked.

The first: “What does this RFI sound like to you?” And sometimes a video or screen capture is included when an amateur reaches out about their interference problem. The question then becomes, “What does this look like to you?”

Aside from a few very distinctive types of RFI, it is difficult to identify what specific device is causing interference based on the sound it produces, or the visual signature in a waterfall.

The most useful question to ask first regarding interference isn’t “What is producing this RFI?” 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 is much easier.

For example, at my own station, there are no fewer than 20 individual devices that can potentially cause RFI (and some do!). This is just one room in one house, in one of many houses in the neighborhood.

In my case, figuring out where interference is coming from is easy: it’s my own home. It wasn’t difficult for me to locate individual sources of RFI and deal with them on case by case basis as I worked on reducing interference around my station.

Another example: Let’s say I use a very popular imported LED bulb in my home and it’s producing RFI. Let’s call it part of the DimBulb brand, model no. 123A. I purchased the bulb online. There is no question that this bulb is the source of my noise, and I can deal with it.

Although this is an imaginary brand and model number, the potential for one of those bulbs to be in service in your neighborhood, with many homes nearby, is highly likely. Even knowing without a doubt the source of RFI is that very same bulb, would you ask all your neighbors if they have one of those bulbs? Would they even know offhand if they did? Or would you locate where the interference is coming from and then determine what is causing it?

Rather than trying to figure out what you think is causing interference and chasing after that particular device, you’re better off tracking down where RFI is coming from and going from there. Try to ask yourself “where” before asking “what.”

Almost half the RFI cases of unknown origin I deal with are found to be in the amateur’s own home. Never underestimate the power of simply taking a trip to your main breaker and listening for noise on batteries. It’s the best first step when determining “Where is this RFI coming from?” before figuring out “What is causing this RFI?”      


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

Links to all other Common Point Shows are available at Simsbury Community Television.  Common Point is a show for and about communications.

Links to other videos include:

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.

About Amateur Radio.  Featuring ARRL Laboratory's Bob Allison, WB1GCM. From Simsbury Community Television's, Common Point, Produced by Dan Thomas, NC1J


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.

Web Links

Information for Electric Utilities


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.