[SI-LIST] Re: Why shielded twisted-pair is still twisted?
- From: Colin Warwick <colin.a.warwick@xxxxxxxxx>
- To: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
- Date: Fri, 14 May 2010 20:17:23 -0400
Not so, Charles. Alexander Graham Bell invented the twisted pair with the
specific goal of reducing interference. He was granted US patent 244,426 in
1881 for the invention.
-- Colin
Blog http://signal-integrity.tm.agilent.com
On Fri, May 14, 2010 at 9:33 AM, Grasso, Charles <
Charles.Grasso@xxxxxxxxxxxx> wrote:
> 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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