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I was looking at buying a USB Isolator; however, I ended up buying a powered four port USB 3.0 instead. It was roughly the same price, has a higher speed, and serves a useful alternative function.

Do these two devices work any differently. They're both powered externally? Will both of these be equally effective at eliminating a ground loop?

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A USB hub will probably tie all the grounds together, so that won't help you break your ground loop.

Update: I just checked a Belkin F5U701 hub with my multimeter (in continuity mode). The grounds of all the USB ports are tied together and tied to the ground of the power supply.

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  • Why would they do that if it takes an external power supply? Why not just use the ground from the transformer? – Evan Carroll Oct 31 '12 at 21:34
  • I can't help you with the why part - better to ask at electronics.stackexchange.com, where people with experience designing USB hardware can answer. I updated my answer with some information about a hub that I have lying around. – ObscureRobot Oct 31 '12 at 23:23
  • @EvanCarroll It's much simpler. The actual data signal levels are relative to ground, so if they wanted to separate the grounds they'd have to convert the signals as well — all of which is extra complexity mostly unrelated to the digital-logic-type functions of a USB hub per se. – Kevin Reid Nov 1 '12 at 1:41
  • hrm... why are digital signals relative to ground? I thought that was a function of analog signals. I thought digital signals were on or off? Sorry if it's a stupid question, I don't work on such low levels though. – Evan Carroll Nov 1 '12 at 2:48
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    Digital signals are a special case of analog signals. Voltage is a potential difference, so you need something to reference your signal against. – ObscureRobot Nov 1 '12 at 5:25

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