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USB Extension cable and performance
WhereEaglesDare:
--- Quote from: Ed_McCarron on May 01, 2010, 11:58:35 am ---
--- Quote from: WhereEaglesDare on May 01, 2010, 11:07:16 am ---splice in some cat5e to make it long enough, and see if it works
--- End quote ---
I bump into this constantly. People assume "Well, cat5 is rated to 100Mhz, so it must be good cable to use for -X-" -- but the truth is that cat5 (and most UTP cables) are useless without the differential drivers at each end.
A nice low cap shielded cable would fit the bill better.
--- End quote ---
I am pretty sure that Cat5e (e = enhanced) is rated for 350MHz. I have used it several times for this purpose and no problems when the PC can handle that long of an extension.
MonMotha:
CAT5e is rated for 350MHz. However, the characteristic impedance does not match USB specifications, and the splices will introduce all sorts of nastiness. Also, high-speed USB 2.0 is >350MHz. Just use a real USB cable. USB *is* differentially signaled, but the cable characteristics it expects are not those of CAT5e. USB cables are also shielded, which standard UTP CAT5e is not (the 'U' means unshielded).
There's a difference between "yeah, this often works" and "this should always work". The specification is deliberately conservative so that things should always work. The physical electrical/cabling section is quite informative. I suggest reading it if you're interested.
All this said, you're not likely to damage anything messing around with this stuff. Feel free to experiment. Just remember that everything you're doing is against the specification and by no means guaranteed to work right.
Ed_McCarron:
--- Quote ---CAT5e is rated for 350MHz.
--- End quote ---
Heh, my TDR only tests out to 100 Mhz -- it was around before 5e existed.
--- Quote ---Just remember that everything you're doing is against the specification and by no means guaranteed to work right.
--- End quote ---
This is very true -- that ethernet run won't mysteriously stop working at 329 feet -- just don't call me back to run new cable if it doesn't. :)
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