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In my design I have a national instruments chassis (cDAQ 9132) inside of a closed rack fixture. I want to be able to access the usb port on the NI chassis from a front panel on the external of the rack. My thoughts were to just connect a male-to-male usb cable from the NI chassis into the front panel via a panel mount usb connector.
My question is, will the usb extender and connector cause signal degradation? The total length would only be a few feet, much less then the 5 meter maximum.
From my experience, USB extender cables work, with caveats.
A device I have draws 460mA out of the allowed 500mA. It will only work with good quality cables (ie, with enough copper in them), no extenders, and only some ports on the PC (those on the mobo, not those on the front, which go through more cables). Contact and wire resistance matters...
Less power-hungry devices will cause less problems.
USB Bulk mode retransmits packets when an error is detected.
If your device uses bulk mode, a little more bit errors will reduce throughput (slightly). If there are enough bit errors to make enumeration fail, though, it won't work at all.
I have used extenders with high speed devices without problems.
When you think about it, the USB connectors on the front of your PC go through an extender cable... and they're connected to the mobo with 0.1" headers, which I honestly doubt respect the USB impedance spec...
Why not try? I'm pretty sure it will work, as long as all connectors are USB certified.
You are essentially asking if you can use a USB 2.0 extender cable in your setup. The answer is "it depends".
First, formally the USB specifications disallow cable extenders, for the reason that every extra cable imperfection (two extra connectors and two cable fan-outs at solder joints inside cable molds) usually degrade the high-speed signals beyond acceptable. Quality of extenders, however, vary greatly, so your mileage can vary.
Then, it depends whether you/your users/customers are going to plug USB devices with extra long 5-m cables. Then your extra extender will likely kill the USB functionality in high-speed mode. You will have flaky behavior, with unpleasant experience, data corruption, etc. Contrary to the belief in USB data recovery mechanism, it works only in a narrow region of degraded signals. If the channel gets degraded a bit deeper (due contact wear, contamination, different mechanical tension), the channel will just drop off, reconnect back, and cause a lot of troubles.
However, if you plan to use only LS/FS USB devices (mice/keyboards/sound) the extender will be fine.
The hopes that USB port will fall-back into FS mode are also unfounded. The reason is that the FS-HS negotiations are coming at a relatively low signal speed (~20kHz) where the signal degradation is negligible, so the initial connection will be always negotiated as "HS mode", and the link will always start in HS at 480 Mbps. Then the channel will see massive transfer errors, and host will try to recover the port by resetting/re-enumerating it, and process will fall into the same loop.
