I need to pass a USB cable through a vacuum chamber wall, for which we have only D-SUB passthrough flanges available. So I cut a USB cable in half and soldered a D-SUB connector to each half. For USB 2.0 connections, this works without any issues, but I've had troubles getting a USB 3.0 connection to work.
Specifically, the computer emits the connect/disconnect sound repeatedly every few seconds when the cable is plugged in. The only workaround is to push the connector in slowly, until the device is recognised, essentially forcing a USB 2.0 connection.
I assume this is due to insufficient shielding to get a USB 3.0 link?
The individual connections seem to be fine, with <3Ω resistance for each one and no shorts. Below is a diagram of how I routed the cables through the connector:
As shown in the figure, the shield is connected to the shell of the connector to connect the shield on both sides together. I tried to keep the amount of destroyed shielding low, with around 3cm on either side removed.
What is the most likely cause for this failure, and how to avoid it in the future, if possible?
Best Answer
It's more likely that you simply introduce an impedance break so significant by separating the conductor pairs of the superspeed conductors that communication can't properly take place.
As said, you can't just separate the conductors of USB3 arbitrarily: the signal is carried as electromagnetic field between the conductors; because the signal frequencies of USB3 are solidly within the microwave range, your splitting of conductor pair essentially means you break the transport of energy.
You probably won't be able to solve this situation using your current D-SUB connectors at all. You'll need to replace these connectors with ones that at least approximately retain the nominal 90Ω impedance of USB3 SS connector pairs. It's pretty likely the easiest way to achieve that is through USB3 connectors themselves.