Too much noise killed my Zigbee network

Back in the days of USB-A being the actual standard and spread across every single electronic device, life was easier.

We could be talking about how USB-C is great nowadays. It’s a single actually universal port that most of our digital gadgets share. But “USB-C” only tells part of the story. If you dig a little deeper, you will find many different approaches to what seems to be a universal port: USB 2.0, 3.0, 3.1 Gen 1, 3.2 Gen 2, 3.2 Gen 1x1, USB 4, etc. Some support data and power, others are specifically designed for extra power, called power delivery.

Then there’s Thunderbolt. Apparently (and I could be wrong here) USB 4 can do what Thunderbolt does, but most of it is optional.

Put shortly, USB-C just means “the oval reversible port.” What that port is capable of doing is a whole other story.

But we’re not here to talk about this, even though there’s plenty to cover, as you can see.

We are here to cover something else. Something that I don’t ever recall seeing or hearing about, even though I have been playing with computers for as long as I can remember. And I’m almost 40 at this point.

The setup

The other day I finally got an HDD delivered that I had ordered back in February. This is a 10 TB drive, meant to be part of my backup strategy.

At that time I had also ordered a small plug and play SATA dock so that I could place the dock next to the NAS (key part), connect them via USB 3, and do a full backup to the external drive. Seemed simple enough to me.

But there’s an interesting catch. I’ll tell you first what happened and you try to figure this out before I tell you about it.

The meltdown

So I plugged everything in, opened a new terminal window on my computer, connected to my NAS with SSH and ran the script that runs rsync to copy everything to the external HDD. So far so good. I could see files being transferred, which files they were and where they were going. Looks good to me!

A few minutes later my wife arrives home. As usual, she picked up her phone and pressed a toggle that opens the driveway gate. Except this time the gate didn’t move. I had flashbacks of that other recent episode. I tried to do it myself through my phone. Same story. The gate wasn’t going anywhere.

We had better things to do at the time so the car got parked outside and we moved on.

And by “moved on”, I mean, I sat down at the computer banging my head trying to figure out what was going on. Home Assistant itself was up and running, and apparently working fine. Since Home Assistant is running inside the NAS, I thought that for some odd reason rsync could be eating up so many resources that Home Assistant wouldn’t be able to do anything. But that was not the case. Even after stopping the backup, the gate wouldn’t open.

Not only that, I eventually noticed that the lights were also not turning on or off. So it’s not just the gate now. Absolutely none of the Zigbee devices were working: lights, gates, plugs, sensors… they were stuck at whatever state they currently were.

The rabbit hole

I tried to access the management portal for my Zigbee coordinator and that was accessible. Did a reboot. Nothing changed. Then I rebooted Home Assistant. Nothing changed. Lastly I rebooted the NAS itself. Still nothing changed.

I had a firmware update to do on the Zigbee coordinator and I thought it could help with some extra stability, so I did it. It didn’t help.

Then I went back to Home Assistant, settings and then Zigbee settings. Everything was reporting as being online and working. But it wasn’t. Then I checked network information and clicked the “change channel” pencil icon. And noticed a big message including this bit:

Only change your Zigbee channel after reducing other 2.4 GHz interference, for example by using a USB extension cable and keeping the coordinator away from USB 3.0 devices, SSDs, and nearby Wi-Fi.

The clue

Can you see where we are going already? It’s exactly what you are thinking. The USB 3 HDD dock was placed right next to my NAS. Which happens to be just about a fist away from the Zigbee coordinator. But why is this relevant anyway?

Well, if you are like me and never heard about this, brace yourself because you’re in for one hell of a ride!

Apparently, Intel themselves have published a research document explaining just how USB 3.0 devices can interfere with 2.4 GHz wireless devices. Can you guess what frequency Zigbee operates in? Ding ding ding!! 2.4 GHz!

Let me say that again!

A USB 3 hard drive—a device that has no Wi-Fi whatsoever—can interfere with an existing wireless network by producing noise in the same frequency. How insane is that?

Specifically, the paper mentioned above notes that the noise floor rises ~20 dB near an external USB 3.0 HDD, and ~25 dB at a notebook USB 3.0 receptacle.

My Zigbee dongle was plugged into the router, which sat right next to the NAS. The coordinator was literally a fist away. And right there, an HDD dock running backups via USB 3.

I couldn’t figure out why devices kept responding late or not at all. Range was fine, the mesh looked healthy on paper. But every time the backup kicked in, everything fell apart. Turns out the USB 3 noise was blasting straight into the 2.4 GHz band, drowning out the coordinator.

The fix

Moving the HDD dock just about 40 cm away from the Zigbee coordinator fixed it instantly. Like magic.

Now you know! A hard drive can break your smart home without ever touching the network. And it’s not just Zigbee that suffers, your 2.4 GHz WiFi can take a hit too, with slower speeds, dropped connections, or flaky performance that seems to come out of nowhere. In my case the router was sitting right next to the NAS, with the Zigbee dongle plugged directly into it. Between the USB 3.0 noise from the HDD dock, the router’s own 2.4 GHz radio, and the coordinator packed into the same tiny space, the whole band was a mess.

If your wireless devices ever go flaky for no apparent reason, take a look at what’s sitting next to your access point or coordinator. It might just be a USB 3.0 cable a few centimeters too close.