Eric,
this 150 ohm story of STP cables sounds completely new to me. Also, my
understanding is that both UTP and STP are used for 10bT ethernet.
In the STP definition of IEEE802.3, there is no mention about different
characteristic impedances from the required 100ohm of 10bT.
Unfortunately I haven't yet received an answer to my original question as
to how STP cables should be actually made (shielded twisted pairs vs
overall shield) .
As I already said in previous e-mails, the "STP" cables that I got look
pretty much the same as "FTP" cables, that is they have just an overall
shield (aluminum foil) around all wires. And they are all declared to be
100 ohms.
Paolo
At 16:56 06/09/2001 -0400, you wrote:
Paolo,
You may want to check if the FTP cable has a 100 Ohms characteristic
impedance which would make it compatible with interfaces designed for UTP
cable. STP cable is supposed to have a 150 Ohms impedance which is not
compatible with standard 10baseT interfaces which are usually designed for
UTP.
Eric
===================================
Éric Meunier
Hardware Architect
E-mail: eric.meun...@ca.kontron.com <mailto:emeun...@teknor.com>
Kontron Communication Inc. (Teknor)
616, rue Curé-Boivin
Boisbriand, Québec
Canada, J7G 2A7
Tel: 1-450-437-4661 ext. 2419
Fax: 1-450-437-8053
Web: http://www.teknor.com <http://www.teknor.com>
-----Original Message-----
From: Paolo Roncone [SMTP:pronc...@cisco.com]
Sent: Thursday, September 06, 2001 4:18 AM
To: Doug McKean
Cc: EMC-PSTC Discussion Group
Subject: Re: STP vs FTP Ethernet cables (2)
Doug,
I re-paste the first part of the definition in IEEE 802.3 (2000):
<<1.4.249 shielded twisted-pair (STP)cable: An electrically
conducting cable,comprising one or more ele-
ments,each of which is individually shielded.There may be an overall
shield,in which case the cable is
referred to as shielded twisted-pair cable with an overall shield
(from ISO/IEC 11801:1995)>>
My understanding is that "elements" should refer to individual PAIRS
(signal/return), rather than single wires. But - as I said in my previous
e-mail - I'd like to check whether this is put into practice by some
vendors. So far I didn't get any clue on this.
The STP cables that I found so far (form a couple of vendors) have
just an OVERALL shield around all wires, and these are identical to FTP
(Foiled Twisted Pair) cables that are also on the market.
I agree with you, something doesn't sound right...
Paolo
At 09:36 05/09/2001 -0700, Doug McKean wrote:
Paolo Roncone wrote:
>
> The reason of my inquiry is that we bought samples of
"STP" and
"FTP"
> cat.5 cables for 10bT ethernet applications from different
vendors
and to
> our surprise we discovered that both "STP" and "FTP" types
have an
> overall (external) shield made of aluminum foil, but no
shields on
individual
> wires or wire couples (as per 802.3 definition above).
Maintaining a characteristic impedence of a twisted pair
by shielding the individual wires of that twisted pair?
Something doesn't sound right.
- Doug McKean
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Paolo Roncone
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Technical Committee emc-pstc discussion list.
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Paolo Roncone
EMC Compliance Engineer - Cisco Photonics Italy
via Philips 12 - Monza (MI) 20052
mailto:pronc...@cisco.com
phone: +39 039209 1538
fax: +39 039209 2036
