Consumer electronics products are not known for being particularly well-shielded for radio-frequency (RF) interference – either to protect them from interference from other sources, or to prevent them from being sources of interference to other systems.
Apple has pointed out that some USB 3 devices can generate RF interference around 2.4 GHz, which is the frequency used for Bluetooth (2.4 to 2.485 GHz) and 2.4 GHz Wi-Fi. At its worst, this can disrupt Bluetooth and Wi-Fi connections between a Mac and other devices. Although I doubt very much that this accounts for the continuing problems with Sierra dropping and re-establishing Bluetooth connections, in some situations this could be very significant.
Suggested solutions include:
- Use a longer USB cable so that you can place the USB 3 device (peripheral) far away from your Mac’s Wi-Fi and Bluetooth aerials. Avoid moving the peripheral behind the Mac, or near the hinge of a laptop model, as those are close to the Mac’s aerial. The snag with this is that cheaper USB cables can sometimes act as an antenna, and a longer cable might make the interference worse. Placing the peripheral behind a substantial object, or a pile of books, for example, might reduce adverse effects. This is not helped by the placement of USB 3 and USB-C ports on iMacs, though, as they are on the back, close to the aerials.
- When connecting USB 3 devices to a USB-C port, Apple recommends using the front port on the left-hand side, or any USB-C port on the right side of the Mac. Again, these are furthest from the aerials.
- Switch your Wi-Fi base station to use the 5 GHz band instead of the 2.4 GHz one. This interference seems markedly worse around 2.4 GHz, and not a problem at 5 GHz. Unfortunately, there is no such option with Bluetooth, which is tied to the 2.4 to 2.485 GHz band.
If you are experiencing Wi-Fi or Bluetooth problems and have any USB 3 peripherals, this is worth bearing in mind. If you don’t suspect RF interference, you are likely to find it impossible to fix the problem.