Thread: UTP Cable Wiring Nightmare
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Old 16-02-2013, 11:34   #11
Jon T
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Re: UTP Cable Wiring Nightmare
It's not just the rating of the cable that is the determining factor. Length and course of the cable run and quality of the connections at each end can and do effect speed.

Each of the four pairs of a UTP cable had a different twist ratio to minimize crosstalk between pairs. Obviously to terminate the cable you have the untwist each pair in order to terminate, it's this "untwisting" thats probably causing you problems.

Short cable + bit of crosstalk = still an acceptable signal to noise ratio for 1GB speeds

longer cable + bit of crosstalk = higher signal to noise ratio, so equipment negotiates down to 100Mb(as it can work with the higher SNR)

*also as stated by MJPS, final route of the cable can also have the same effect, don't run UTP parallel to electrical cable, or even worse, over florescent lights and switch mode power supplies.
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