understand the different twist-rate of cable-pairs in twisted pair cable - Page 1
Forum section: electronics / beginners

author: m4rtin
author_rank: Regular Contributor
timestamp: March 26, 2015, 09:12:54 pm
content: According to WikipediaWhen nearby pairs have equal twist rates, the same conductors of the different pairs may repeatedly lie next to each other, partially undoing the benefits of differential mode.How same conductors of the different pairs undo the benefits ofdifferential modefor example in Cat5e cable?

author: linux-works
author_rank: Super Contributor
timestamp: March 26, 2015, 09:34:19 pm
content: differential mode works when both wires are 'hit' by radiation equally.if you have one of the members of the pair closer to the signal interference source than the other wire, they are no longer 'hit' equally and you can't subtract out (as well) the common-mode noise component.I don't think 10/100 cat5 cable has asymmetric twists (not sure) but I know that gig-e (5e or 6) does play that 'unequal distance' game. ie, some pairs end up being slightly longer due to having more twists than other pairs. interesting bit of trivia for layer1 networking folks(also that is a good reason not to use cat5e or cat6 patch cords for joining things that need to arrive at exactly the same time, such as audio i2s. its somewhat fashionable to use rj45 jacks and ethernet wire to connect high end dac and transports together, and for very short runs, its ok; but its still technically 'wrong').

author: m4rtin
author_rank: Regular Contributor
timestamp: March 26, 2015, 10:34:22 pm
content: Quote from: linux-works on March 26, 2015, 09:34:19 pmI understand, but IMHO this explains why wires are twisted in the first place. This doesn't explain why wire-pairs have different twist-rate.

author: grumpydoc
author_rank: Super Contributor
timestamp: March 26, 2015, 10:39:20 pm
content: Quote from: m4rtinIf they had the same twist, two pairs could interlock bringing the conductors closer togetherWith different twist rates this doesn't happen.Quote from: linux-worksIt does, seehttp://en.wikipedia.org/wiki/Category_5_cable

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: March 27, 2015, 05:15:32 pm
content: I got a free section of a spool of cat6e (seriously, IT departments throw away like half the spool!) and it actually has a plastic '+' shaped divider going through the cable to seperate each twisted pair from each other. I think these cables are rated for 10gb/s data trsnsfer rates. I dont remember if the twist rates are different though. I have always wondered how on earth are these cables made? I couldnt come up with any ideas on how they produce such a massive contiuous length of twisted, insulated, divided, and then another layer of insulation over the entire cable...

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 27, 2015, 05:26:44 pm
content: Note that the four pair in a Cat cable have SLIGHTLY DIFFERENT twist rates specifically to avoid this problem.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 27, 2015, 05:32:26 pm
content: Cat6 cable production video -More here as well -

author: SeanB
author_rank: Super Contributor
timestamp: March 27, 2015, 05:34:11 pm
content: Quote from: iamdarkyoshi on March 27, 2015, 05:15:32 pm

author: m4rtin
author_rank: Regular Contributor
timestamp: March 28, 2015, 01:59:51 am
content: Quote from: grumpydoc on March 26, 2015, 10:39:20 pmThanks! So in a nutshell, cables within pairs are twisted in order to distribute noise as equally as possible between two members of the pair so that differential signaling will work properly? And cable pairs are twisted with different twist rate so that two or more pairs do not interlock which would bring conductors of different pairs closer together?

author: digsys
author_rank: Unknown
timestamp: March 28, 2015, 02:33:20 am
content: If you want the ultimate, you can use individual shield type. A bit pricy.