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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