That radio interference might be coming from your cheap USB charger

In modern vehicles, people are more dependent than ever on the presence of a phone or tablet. Most new vehicles come with some sort of USB charging port that may even include USB communication to an in-vehicle infotainment system, allowing for streaming video, representation of CarPlay mapping on the vehicle display, etc. As consumers, we’re now accustomed to getting into a vehicle, plugging in our phone, and having that phone seamlessly connect and work with our vehicles.

But what if you don’t have a newer vehicle? What if your car, aircraft, RV, truck, or tractor was built before USB integration was a common customer expectation?

Well, if you’re like most you go buy an adapter that lets you plug in one or two USB devices through the auxiliary power outlet. These outlets, which you might call a cigarette lighter socket, were originally designed to power electrically-heated cigarette lighters but have since become interfaces where we all commonly plug in USB charging adapters.

When shopping for a USB charging adapter you encounter a shockingly wide array of prices for such devices. Many options are available at discount stores or online for as little as $2.00.

However, check out this USB charger manufactured by Genuine Volkswagen and Audi, MSRP $54.00. What is with the 25x markup from Audi on their USB plug? While it is possible that there is more margin stacked up in that automotive USB plug than in an online merchant’s unit, there is much more to this story. It can be simply summarized as:

The Audi plug meets automotive standards. The other plugs do not.

That means that the Audi charger has been rigorously testing against standards from both regulators and the vehicle manufacturer themselves. The cheap adapters have an ambiguous level of testing and are self certified by the manufacturer (with no regulator or manufacturer oversight).

So what?
For automobiles in which USB charging ports are integrated by the manufacturer, they are tested against automotive standards. These standards ensure the devices are fit for the environment and will produce a high-quality customer experience. For example, it is inconceivable that plugging a phone or tablet into the manufacturer’s USB port would cause interface on AM, FM, or two-way radios. Plugging in a device and getting a bunch of static on the FM radio or completely losing two-way radio communication is intolerable.

This is, however, a common occurrence when using charging devices that are not designed for automotive use. A lot of these chargers carry FCC/CE marks, look safe and legit, but ultimately damage your ability to receive and transmit radio communications. This could be as benign as negatively impacting your ability to receive an AM radio station, or as painful and inconvenient as knocking out two-way radio communication completely — especially if that is your aircraft VHF comm.

What do I do about it?
Not all chargers are created equally. There are absolutely some high quality products available through online retailers that won’t cause radio noise. Unfortunately there’s really not much one can do to qualify such a charger when shopping, and the only practical way for pilots to sort through them is to buy them, put them in the aircraft, and see what happens. Many of these chargers will cause radio noise, and that noise will vary from slightly inconvenient to completely unmanageable.

Here are a couple of things to take into consideration when making that choice for your aircraft:

  • USB charging technology changes VERY quickly. Just because you bought a charger from a specific brand and it worked, that does not mean that going back to the same supplier next time will provide a product that provides clean power without radio noise. This is because consumer devices are not governed by the same kind of engineering change control and certification practices as products that are regulated by folks like the FAA, or closely monitored by aircraft/vehicle OEMs with good design change control. A lot of consumer devices will roll fast with changes to new technology but repackage in the same tooling — therefore, buying what appears to be the same device might all of a sudden produce lots of interference.
  • Vibration activity in aircraft and cars is very different. A lot of consumer-style USB chargers are generally designed in a manner that will be friendly for an on-road automotive experience. It’s a much different environment in the ‘74 PA-28 or M20B that you fly around on the weekends. Aircraft vibratory loads can be rough on devices that are not designed for them, so you might burn through cheaper chargers not designed for the environment rather quickly.

If you really need the radio, and to power a device in the aircraft during flight, you should make sure you can do both with a lot of confidence and use a manufacturer-provided solution (in a new aircraft or service part), or purchase a certified charger that you know is going to work and deliver a consistent experience if it is ever replaced.

Then you’ll absolutely have a charging solution that will allow you to aviate, navigate, and communicate without worrying about losing that last word along the way.

Video examples of radio interference

Check out this experiment after he experienced interference in his RV:

For a deeper dive, watch this video from Kenwood (a radio company). They produced a demonstration with a two-way radio, which is a low-frequency radio (typically between 151 and 154 MHz) that operates in bands similar to those used in aircraft.

David Batcheller – President & CBO