USB 3.0 Hubs: Noisy or Not?

USB 3.0 Hubs: Noisy or Not?

While I’m not the first to post on the topic of USB3 hubs causing interference in 2.4 GHz, I thought I would add my experience to the mix. Here are a few quick reads for your interest:

“USB 3.0 Radio Frequency Interference on 2.4 GHz Devices” from Intel

“USB Hub – Interference” by Nolan Herring

“Shielding Resolves USB 3.0 Conflict with Bluetooth” from macscales.com

I first noticed something strange in Ekahau Site Survey, using a 7-port USB 3.0 hub from Orico. My signal-to-noise ratio was negative (noise higher than signal)! What the heck, eh? The ever-helpful WLAN pro community on Twitter was quick to respond to my query, informing me that USB 3.0 hubs are not to be trusted for surveying. I followed up recently with some testing.

Test Setup

I was at the family cabin, where we don’t have our own internet connection. The neighbors do, however, with their router set to channel 6, and I can pick it up in our kitchen. I also set my phone’s hotspot to channel 1. My test setup consisted of:

With both laptops side-by-side on the kitchen table, the networks looked like this in WiFi Explorer on the MBP.

wifi explorer test enviro

Test networks in WiFi Explorer on MacBook Pro

Here is the view in Acrylic WiFi on the XPS 13.

Acrylic test enviro xps

Test networks in Acrylic WiFi on XPS 13

ESS Measurements

Next, I took measurements in ESS on the MacBook with the NIC-300 connected with no hub, with the USB 2.0 hub, and finally with the USB 3.0 hub. Because the NIC-300 is plugged into the hub, the placement of the hub (velcro’d to back of display, sitting on desk, etc) is inconsequential. Here are the results in that order.

ESS signal levels, MacBook, no hub

ESS signal levels, MacBook, no hub

ESS noise levels, MacBook, no hub

ESS noise levels, MacBook, no hub

ESS signal levels, USB2 hub, MacBook

ESS signal levels, MacBook, USB 2.0 hub

ESS noise levels, MacBook, USB2 hub

ESS noise levels, MacBook, USB 2.0 hub

ESS signal levels, MacBook, USB3 hub

ESS signal levels, MacBook, USB 3.0 hub

ESS noise levels, MacBook, USB3 hub

ESS noise levels, MacBook, USB 3.0 hub

So, when attached to the MacBook Pro, the USB 3.0 hub was causing a roughly 20 dB increase in the noise floor! It also made the RSSI appear around 10 dB lower than with the USB 2.0 hub or no hub. I did the same tests using the XPS 13. Here are those results.

ESS signal levels, XPS13, no hub

ESS signal levels, XPS 13, no hub

ESS signal levels, XPS13, no hub

ESS noise levels, XPS 13, no hub

ESS signal levels, XPS13, USB2 hub

ESS signal levels, XPS 13, USB 2.0 hub

ESS noise levels, XPS13, USB2 hub

ESS noise levels, XPS 13, USB 2.0 hub

ESS signal levels, XPS13, USB3 hub

ESS signal levels, XPS 13, USB 3.o hub

ESS noise levels, XPS13, USB3 hub

ESS noise levels, XPS 13, USB 3.0 hub

Using the USB 3.0 hub and Dell XPS 13, there was no effect. I thought I saw the noise bounce up for a split second, a few times, it didn’t last. However, that was enough for me to write off the USB 3.0 hub for surveying.

Chanalyzer Measurements

The next part of my test involved using Chanalyzer to look at the change in the noise floor depending on the position of the USB 3.0 hub, using both the MBP and XPS 13. I stuck the DBx on the velcro on the back of the displays and plugged it into a port on the laptop. I then took measurements with the hub sitting on the desk in front of the laptop, and again with the hub stuck to the velcro as one would do whilst surveying. I was focused strictly on the noise floor for these measurements. The following images show those setups.

MacBook with USB3 hub on desk

MacBook with USB 3.0 hub on desk

MacBook with USB hub on velcro

MacBook with USB 3.0 hub on velcro

XPS13 with USB3 hub on desk

XPS 13 with USB 3.0 hub on desk

XPS13 with USB3 hub on velcro

XPS 13 with USB 3.0 hub on velcro

The next image shows the 2.4 GHz spectrum without the USB 3.0 hub plugged in. The noise floor is in the neighborhood of -100 dBm, and you can see faint outlines of the signatures from the router on channel 6 and my phone on channel 1.

dBx MBP no hub

2.4 GHz spectrum with DBx plugged directly into MacBook

In the next image, look at the noise floor with the USB 3.0 hub plugged in but sitting on the desk in front of the laptop. The noise floor is slightly higher. I also remembered to turn off my phone hotspot and most of the other devices in the area.

MBP hub on desk

2.4 GHz spectrum, MBP, USB 3.0 hub on desk

Now, see what happens to the noise floor with the USB 3.0 hub stuck on the velcro, right beside the DBx, where it would likely be for a survey.

2.4 GHz spectrum, MPB, hub on velcro

2.4 GHz spectrum, MPB, USB 3.0 hub on velcro

Here’s another look from the RTFM in ESS. The noise floor in the spectrum side on the left doesn’t look as high as it shows up in the scanning side on the right.

2.4 GHz spectrum in ESS RTFM from MBP

2.4 GHz spectrum in ESS RTFM from MBP with USB 3.0 hub on velcro

The noise floor has come up 10 dB. Now, a noise floor of -90 dBm doesn’t seem that bad for a production environment, but when you pair these results with the noise levels reported by ESS, there is definitely a problem. I’d love to repeat these tests using a Cisco AP with Clean Air, to see if the increased resolution picked up something else going on in the spectrum view.

The next two images show the spectrum with the hub and DBx plugged into the XPS 13. The first image is with the hub on the desk. The second is with the hub on the velcro, beside the DBx.

2.4 GHz spectrum, XPS13, hub on desk

2.4 GHz spectrum, XPS 13, USB 3.0 hub on desk

2.4 GHz spectrum, XPS13, hub on velcro

2.4 GHz spectrum, XPS 13, USB 3.0 hub on velcro

As with the results from the ESS measurements from the XPS 13, there is no perceivable change to the noise floor. Based on the Intel white paper, my guess is that the XPS has betting shielding or grounding on the USB 3.0 connectors, than the MacBook does. Now, I don’t really survey with my MBP due to the weight difference, but I still would rather avoid any chance of having my data messed with on the XPS.

So, I have purchased the 4-port USB 2.0 hub mentioned earlier. I definitely cheaped out on this hub, and it hasn’t impressed me with it’s build quality. I also overestimated the length of the USB tail, hence the additional right-angle extension cable. These images show what it looks like on both laptops.

MBP with USB2.0 hub

MBP with USB 2.0 hub

XPS 13 with USB 2.0 hub

XPS 13 with USB 2.0 hub

It’s not very elegant, so I’m on the lookout for a good 7 port USB 2.0 hub. When I find one, I’ll be ordering a set of Hub Holsters to replace the velcro. If anyone is using something they like, please let me know in the comments.

In the last few weeks I’ve heard of some people say they have no issues with their USB 3.0 hub, and others say they definitely won’t survey with USB 3.0. If you take anything away from this post, let it be that you always test your equipment before using it in a production environment.

Thanks for reading, and please comment!

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  • Anthony

    It might be obvious, but I noticed the greatest increase in noise when the DBx is connected to the 3.0 hub vs. direct to an available on-board USB interface. I see ~10dB of elevation in the noise floor. Like you I’ll be going back to the USB 2.0 hub.
    The Hub Holster is pretty sweet. I’ve been using a bendable gear tie I found at the Depot by Nite Ize. It’s silicone coated so it grips the hub well while staying out of the way of the usb slots. It hangs on the top edge of my laptop screen and seems to stay put, while also allowing me to have the NICs elevated almost entirely above the screen. Trust me, it’s more ghetto than it sounds, but baby, it works!

    • Anthony, thanks for reading! The gear ties are a nice product for sure.
      I didn’t test specifically for the difference between having the DBx in an on-board port vs. in the 3.0 hub. It was bad enough, using the on-board port, to screw up the RF environment and survey data. I don’t remember if that was oversight on my part, or that I had answered my questions and/or ran out of time.

  • Ken Nadsady

    I have read about the issues being seen with USB3.0 hubs and have been wondering if some hubs are made with better filtering or if some brands may not exhibit the interference at 2.4GHz. I did a quick test using Chanalyzer for a 7-port aluminum body Anker USB3.0 hub that came with my NetScout AirMagnet kit. There was a 0.5 to 1dB difference in the noise floor between the baseline measurement without the USB hub connected and the measurement with the hub inline with the DBx and the antenna of the DBx right against the hub body.
    That does not seem too bad to me.

    • You’re right, that doesn’t seem too bad. I suppose the most important thing would be to test your tools so you know exactly what you have going on. Your hub seems to be ok. In my case, RSSI measurements were very strange in Ekahau Site Survey, and that’s when I pulled out the spectrum analyzer.