Questions about twist rate and position inside twisted pair bundle

Questions about twist rate and position inside twisted pair bundle

Post by ieee s » Sat, 12 Jul 2003 06:59:48



Hi, Folks:

Can anyone tell me where to find information about pair position
inside twisted pair bundle ? For example, inside a 25 pair bundle
24AWG ?

Basically, I want to find the relative positions of different pairs
inside bundle.

My first question is: if two pairs are adjacent to each other at one
location,
                      will they be still adjacent to each other after
                      traveling some distance along cable ?

My second question is:  Will all pairs travel parallel inside a bundle
? or can
                        they exchange position when they travel long
cable ?

My third question is: Is the twist rate, which I mean, the length of
twist,
                      defined by standard ? or manufacturer can define
its own
                      twist rate ?

Many thanks in advance.

 
 
 

Questions about twist rate and position inside twisted pair bundle

Post by lawrence.jo.. » Sun, 13 Jul 2003 01:12:55



> Can anyone tell me where to find information about pair position
> inside twisted pair bundle ? For example, inside a 25 pair bundle
> 24AWG ?

Most manufacturers publish specs.

Quote:> My first question is: if two pairs are adjacent to each other at one
> location,
>                       will they be still adjacent to each other after
>                       traveling some distance along cable ?

Are we talking CAT5 or better, or regular telecom cable?  25-pair CAT5
cables are typically organized into five bundles of four pairs and one
bundle of five pairs.  The pairs in each bundle are twisted together
just like the pairs in an ordinary four-pair cable, so adjacent pairs
stay adjacent.

Quote:> My second question is:  Will all pairs travel parallel inside a bundle
> ? or can
>                         they exchange position when they travel long
> cable ?

In CAT5 cables, the pairs are twisted together, not parallel.

Quote:> My third question is: Is the twist rate, which I mean, the length of
> twist,
>                       defined by standard ? or manufacturer can define
> its own
>                       twist rate ?

The standard just specifies the required electrical properties, it's up
to the manufacturer to decide how to achieve them.

-Larry Jones

In my opinion, we don't devote nearly enough scientific research
to finding a cure for jerks. -- Calvin

 
 
 

1. Unshielded twisted pair vs. shielded twisted pair

Lately I heard of "shielded twisted pair" being used for 10-BASE-T
applications, with the claim that it provided improved noise
reistance.  The only "drawback" mentioned was a reference to the
practice of using 8-pair cable to carry both data and voice (4 pairs
for data, 4 for voice), noting that shielded twisted pair was not
suitable for voice.

Is there any reason (other than increased cost) to _not_ use shielded
twisted pair for an ethernet LAN carrying only TCP/IP traffic?

Finally, on a related note, I found that baluns are available to
permit twinax traffic over twisted pair.  Any experiences with this
would be helpful.

--


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