ANSI X3.263 section 9.1.1.1 specifies that STP interfaces shall be terminated in 150 Ohms and section 9.1.2.1 that UTP shall be in 100 Ohms for qualification testing. It seems that most Shielded Twisted Pair cables on the marked called by the STP acronym are in fact designed according to UTP requirements such that they can be used for standard 10bT applications. I remember seeing a reference about this in a cable catalog, probably Belden, and I was told once that some people got trouble because they had used 150 Ohms STP cable on a 10bT LAN... which all seems to corroborate with the ANSI spec. If someone has time to investigate further...
About the wavelengths comment, I guess it is true that one might typically get away with a few wavelengths for a 1.5 impedance mismatch ratio. However, if you want to be sure you will never get a surprise with equipment interoperability I would guess it is better to avoid such significant mismatch over more than a fraction of a wavelength. Equipment manufacturers design for 100 +/-15 Ohms cable impedance. Has anyone got field experience for large volumes and multiple interface vendors about this? Finally, if you are only concerned about getting a waiver for the Intra-building surge requirement, an overall shield would probably do and should be cheaper. Best regards, Eric =================================== Éric Meunier Hardware Architect E-mail: [email protected] <mailto:[email protected]> 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: Allan, James [SMTP:[email protected]] Sent: Friday, September 07, 2001 9:04 AM To: 'Paolo Roncone' Cc: [email protected] Subject: RE: STP vs FTP Ethernet cables (2) Paolo: Try this link to Quabbin wire company. It is a product selector guide with the types of wire used for different applications. All Ethernet applications are 100 ohm characteristic impedance and only have overall shields if shielded. Telecom cable (T1, DSL etc.) if shielded, are also 100 ohm but the shield (if present) is over the individual wire pairs with no overall shield. I find no reference to standard Ethernet cable at 150 ohms. LINK http://www.quabbin.com/finder/finder.cgi?cmd=app_form Jim Allan Manager, Engineering Services Nextira Solutions LLC 1619 N Harrison Parkway Sunrise, FL, 33323 E-mail [email protected] Phone (954) 846-3720 Fax (954) 846-6282 > -----Original Message----- > From: Paolo Roncone [SMTP:[email protected]] > Sent: Friday, September 07, 2001 5:28 AM > To: "Meunier, Éric" > Cc: [email protected] > Subject: RE: STP vs FTP Ethernet cables (2) > > 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: [email protected] < <mailto:[email protected]>> > > 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:[email protected]] > 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 > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product > Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: > <http://www.ewh.ieee.org/soc/emcs/pstc/> > < <http://www.ewh.ieee.org/soc/emcs/pstc/>> > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: > [email protected] > Dave Heald > [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on > the web > at: > No longer online until our new server is brought > online > and the old messages are imported into the new server. > > > > > > -------------------------------------------------------------------------- > -- > --- > Paolo Roncone > EMC Compliance Engineer - Cisco Photonics Italy > via Philips 12 - Monza (MI) 20052 > <mailto:[email protected]> < <mailto:[email protected]>> > phone: +39 039209 1538 > fax: +39 039209 2036 > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: <http://www.ewh.ieee.org/soc/emcs/pstc/> > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > No longer online until our new server is brought online and the > old messages are imported into the new server. > > > > -------------------------------------------------------------------------- > ----- > Paolo Roncone > EMC Compliance Engineer - Cisco Photonics Italy > via Philips 12 - Monza (MI) 20052 > <mailto:[email protected]> > phone: +39 039209 1538 > fax: +39 039209 2036 > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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