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Message from discussion Cat6A pairs
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John Larkin  
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 More options May 31 2012, 8:57 pm
Newsgroups: sci.electronics.design
From: John Larkin <jlar...@highlandtechnology.com>
Date: Thu, 31 May 2012 17:57:01 -0700
Local: Thurs, May 31 2012 8:57 pm
Subject: Re: Cat6A pairs
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On Thu, 31 May 2012 20:11:48 -0400, Jamie

<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
>hamilton wrote:

>> On 5/31/2012 4:14 PM, John Larkin wrote:

>>> On Thu, 31 May 2012 14:45:55 -0700, John Larkin
>>> <jlar...@highlandtechnology.com>  wrote:

>>>> This is CAT6A FUTP cable, overall shielded but not individually.

>>>> http://dl.dropbox.com/u/53724080/SED/Hitachi_Pairs.JP

>>>> Notice the twist pitch difference. The skew spec is 45 ns max per
>>>> 100M, and it looks to be in that range.

>>> Dropped a "G" somehow.

>>> http://dl.dropbox.com/u/53724080/SED/Hitachi_Pairs.JPG

>>> "Dropbox" indeed.

>>> Doesn't the insulation look a litte fatter on the upper pair?

>> Is there four pair in there ??

>> http://www.jack2rack.com/cat6-bulk-cable/augmented-10gbit/cat6a-plenu...

>That over twist in that one pair, is a manufacturing defect.

The pair twist pitch difference is deliberate in Cat6A-F/UTP, with
only an overall shield. Different pairs have different twists to
reduce crosstalk.

On CAT6A-U/FTP cable, the pairs are individually shielded, so they can
make them all the same twist without a crosstalk penalty. The result
is about 1/4 as much timing skew compared to the cable without
individual shielding... numbers like 12 ns/100m as compared to 45.

My customer bought a *lot* of the wrong cables. I warned them, several
times, that skew could kill this system.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation


 
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