Bluetooth signals can get disrupted on the Ben Franklin Bridge. If it’s not aliens, what’s the cause?

As someone who commutes between Philly and Camden one thing has become predictable in Dan Gibson’s day. His Apple CarPlay and AirPods lose connection near the Camden side of the Benjamin Franklin Bridge, he said.

“There will be no problems for maybe one or two weeks. Then, suddenly, it will start happening again every day,” Gibson said.

Puzzled, the 28-year-old asked Curious Philly, The Inquirer’s forum for questions about the city and region: What’s causing this Bluetooth interference?

The Delaware Port Authority, which manages the bridge, did not respond to a request for comment. Gibson jokingly hopes “it’s aliens.”

For Kapil Dandekar, Drexel University’s interim College of Engineering dean, the cause of the disruption has less to do with intergalactic visitors and more to do with a possible signal jam.

Bluetooth is a type of connection that transfers information and pairs devices without the need for cables or a network.

If the naked eye could catch the transferring process, it would look like ripples in a pond, Dandekar said, one rock thrown in the water generating a patter of waves.

Those undulations represent radio frequencies traveling from one device to another under a radio band.

The Bluetooth signal varies depending on the use. The type of connection necessary for wireless headphones and car stereos is set at around 2.4 gigahertz. This unit determines the frequency and speed of the connection, enabling “a good balance between range and throughput,” according to the Bluetooth website.

Like with ripples in a pond, when bigger or multiple rocks enter the water at the same time, a disruption can happen, resulting in signal interference.

“Instead of having a pattern that kind of moves out uniformly, there’s a lot of chaos that’s introduced,” Dandekar said. “Sometimes that can cause what’s called destructive interference in the signals you’re trying to transmit. That means that you’re going to lose your signal power to the point where communication just is impossible.”

Without the Delaware River Port Authority performing an extensive and costly study, powered by engineers and specialized equipment, it’s impossible to determine a specific cause.

In Dandekar’s experience, the alien stopping Gibson’s music might just be more powerful equipment connections interfering with the strength of his phone accessory’s signal.

Equipment such as the bridge’s own monitoring tools, nearby existing networks, medical equipment, industrial machinery, and even the microwaves in nearby homes or offices could be the culprit.

He equates it to trying to talk to someone in the middle of a house party.

A small group might be able to properly chat and listen to each other. As the party becomes populated, background noise makes listening to other people harder.

“The band starts playing, someone starts using a blender in the other room, and it gets hard for us to communicate,” Dandekar said. “That is the audio equivalent of what’s happening in this radio situation. The signals are just interfering and making communication difficult.”

Much like the party, not all interferences are present at the same time. Bluetooth tries to adapt to the disruption.

Frequency hopping is one of those mechanisms.

Bluetooth signals can jump around from one frequency to another, to try to sense where interference is coming from and adapt. But, there is a limit to how much they can hop around, Dandekar said.

Though no aliens are taking Gibson’s signal, his Bluetooth is fighting its own invisible battle every time he crosses the bridge. The amount of disruptions turned in a particular day and his Bluetooth‘s ability to hop around them are ultimately the difference between him making it to the other side of the bridge with a soundtrack.

“I think I will sleep easier at night,” said Gibson, upon hearing the explanation.