[SI-LIST] Re: Why shielded twisted-pair is still twisted?

  • From: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
  • To: "'Kevin G. Rhoads'" <kgrhoads@xxxxxxxxxxxx>, 'Neo' <neoflash2008@xxxxxxxxx>
  • Date: Fri, 14 May 2010 07:33:30 -0600

Well this has been interesting. In spite of all the excellent physics in these 
answers I would submit that the reason signal pairs are still twisted 
in a shielded twisted pair cable is primarily for manufacturing reasons with
some side benefits for SI which we get for free!!


Best Regards
Charles Grasso


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of Kevin G. Rhoads
Sent: Friday, May 14, 2010 6:21 AM
To: Neo
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Why shielded twisted-pair is still twisted?

>Is this statement applicable to twin-ax cable? For twin-ax case, the outer 
>shield 
>thickness is also just a few mils. Can I say twin-ax also suffer AC power 
>interference?

Simple answer: YES.

But the difference is the ratios between interference frequencies and 
frequencies of
interest.  Audio band INCLUDES 50 and 60 Hz, much of what is run over Twin-ax 
is 
primarily or completely at much higher frequencies.  So separating signal from
interference by frequency is UNdoable for audio and typically trivial for 
Twin-ax
signals.  

Of course, if you want to send unmodulated baseband audio over cable, STP will 
work
better than Twin-ax.

It is a bit like asking if a 240Z is better than a Kenilworth.  What are you 
trying
to do?  Haul heavy loads: Kenilworth.  Drag racing: 240Z.  

Comparisons not only involve the things being compared, they also ALWAYS 
involve a
metric of goodness or worth or value.  So far your metric has been unstated and 
implicit,
so people have been answering in manners designed to allow you to use your 
(unstated)
metric to compare.

There are cases where hum pickup is a total "don't care" and for those any 
proper
metric will assign a zero or negligible weighting to measures of hum pickup.

HTH
Kevin
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