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CHIPS Articles: Electromagnetic Interference in a Home Office Environment

Electromagnetic Interference in a Home Office Environment
By Thomas Kidd - April-June 2020
In the spring of 2020, many office workers around the world suddenly found themselves teleworking. And while most office workers have teleworked before, none had experienced the new normal known as “maximum-telework.” In this article, we discuss an interesting challenge folks may have faced under max-telework: Electromagnetic Interference (EMI), or Radio Frequency Interference (RFI), in the home.

Radio frequencies are a regulated subset of the entire electromagnetic spectrum between 8.3kHz and 300GHz. Interference can come from natural or human made sources, including radio transmitters. Those in the Electromagnetic Spectrum Management workforce are experienced in identifying and mitigating interference sources. The Department of the Navy is the leader in preventing EMI because of the continual challenge in deploying and maintaining an entire city’s worth of radio transmitters and receivers on the deck of a ship.

While our homes are not as complex as an aircraft carrier, we still have many more emitters than one might think. Some are obvious because they have antennae, like our Wi-Fi routers, and some others most consumers might not even be aware of. The following paragraphs address a few examples of EMI which may be found in the home, and how you can be an amateur interference investigator.

Cell phones are both radio transmitters and receivers. They operate across a wide range of frequencies and use sophisticated signals, or “waveforms,” to ensure we have the reception we need any place, any time. Some of us have more than one phone: a personal and work device. A Wi-Fi “hotspot” is also a type of cell phone. Having all these devices close together can lead to many interference issues, especially if the user has a wired headset connected for teleconferences. The buzz-click-click-buzz-click-click sound one might hear in a virtual staff meeting is caused by one of the cellular waveforms. This EMI is most commonly introduced into corded headsets when the cord lays across a cellphone or other cellular device, like a Wi-Fi hotspot. To reduce or eliminate it, move the cord or the other device.

The primary cell antennae is usually built into the frame of the phone, but another challenge with corded headsets is that most smartphones use the cord as an FM radio antennae. There are FM radio apps that will enable listening to FM radio from the phone directly, but, even if the FM radio app is not in use, the antennae connection used by the headset is a vector for interference into the phone. As in the buzz-click-click-buzz-click-click sound example above, the best way to prevent this type of interference is to move the cord.

There is another interference type that can be much harder to detect: interference to the digital part of the phone, the computer’s 1s and 0s that make up the data stream from the phone into the cellular network. This type of interference degrades the performance of the phone, but might not obviously impact call quality. For example, a super high resolution video might not play at full resolution, or at full frame rate. This might be caused by something in the environment interfering with the signal from the cell phone to the cell tower, or it might just be an overloaded internet connection.

If the cause of such digital interference is in the home, there are a few things that can be done to avoid/mitigate it. The first step should be to separate cell phones from Wi-Fi routers. If interference is intermittent, look around to see if a device is being turned on or off at the same time. One of the biggest culprits for EMI in the home is the microwave oven.

While perfectly safe for human use, these devices use powerful radar transmitters to cook food. The device that creates microwave energy is a smaller version of what is used in air traffic control and other radar systems. The brand name for one of the first microwave ovens was the “Radar Range.” Since most microwave ovens are in the kitchen, they aren’t usually near sensitive electronics, like cellphones or computers. However, in multi-teleworker households, under max-telework conditions, the kitchen can double as a home office, with Wi-Fi devices.

There are other less common sources of interference that max-teleworkers might also experience. For example, a malfunctioning piece of electronics can become a source of interference. Similar to the annoying buzz of a failing florescent light bulb, some computers or even audio amplifiers can cause EMI if they malfunction.

Lightning, sunspots, solar flares, and other natural sources can also cause EMI. But these are usually so short, or so big, that it is unlikely they will be the source of isolated EMI in the home. Lightning is a giant spark that creates the crackling sound heard in radios and can introduce interference into long distance telephone systems. Sunspots impact how long range radio communications work, and solar flares or coronal mass ejections can impact everything from satellites to our power grid. But these are large global events and not something we can control around the house.

It is not critical that teleworkers understand all the details of EMI, but by recognizing causes and practicing some simple electronic distancing, it is possible to minimize the likelihood of interference. Not only will devices function better, but colleagues won’t have to listen to that annoying buzz-click-click-buzz-click-click in teleconferences.

Tom Kidd is the director for DON Strategic Spectrum Policy in the Office of the Chief Technology Officer, Department of the Navy Chief Information Officer.

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