EMI Sensitivity of Coax and Twisted Pair wires
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Posted by Ralf Koenig on June 26, 2006, 6:16 am
Please log in for more thread options Hello, I'm looking for a comparison that quantifies the effects of EMI (electro-magnetic interference) on the following media: UTP (Cat.3, Cat.5, Cat.7) STP (Cat.3, Cat.5, Cat.7) Coax RG-58 and RG-59 Fiber Optics There are many qualitative statements on the web, that say that EMI sensitivty decreases when going down the list mentioned above (in other words: UTP is most prone to EM interference, fiber is least or not at all prone to EM interference). I'm looking for references, where I can find a table that gives concrete values or value ranges, such as a book or a web site. Google came up with a lot of results on related issues, none of them actually listing concrete values. Finally, some discussion which kinds of environments (engines etc.) may cause interferences that affect data transfer via these cable, would be most appreciated. Thanks in advance, Ralf | |||||||||||||||||||||||||||||||||||||
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Posted by Dmitri(Cabling-Design.com on June 26, 2006, 6:40 pm
Please log in for more thread options Ralf Koenig wrote: > UTP (Cat.3, Cat.5, Cat.7)
> STP (Cat.3, Cat.5, Cat.7) > Coax RG-58 and RG-59 > Fiber Optics > There are many qualitative statements on the web, that say that EMI
> sensitivty decreases when going down the list mentioned above (in other > words: UTP is most prone to EM interference, fiber is least or not at > all prone to EM interference). I doubt you will find many reliable references let alone numbers. A test like that is extremely hard to produce and maybe harder yet to verify. Also, cabling manufactures are rarely if ever have access to equipment and facilities required to conduct such tests, especially RF. I have seen tests done (even took part in one many years ago) but the results were very dependent on the environment the tests were conducted in. The one I've assisted to conduct was strictly RF, so I would not necessarily project the results onto low frequency noise from likes of power cables and fluorescent lamp ballasts. However, for RF it boils down to this: before your UTP (CAT5E and CAT6 - have not seen this done to CAT3) cable will pick up enough noise your equipment -PC and pretty much everything else - will fail (and people flee ;-)) because you are talking way beyond FCC and EC allowed levels. You will never encounter such high levels of EM fields in commercial and residential environments so there is really no need to worry about the cable. Let me re-phrase that: worry about the electronics before worrying about the cable. If you are in a special environment (industrial, science lab, ship, plane, spaceship etc.) - you are on your own. Feel free to conduct your own tests and come up with your own results - no cable manufacturers will ever guarantee anything or even conduct such (very expensive to setup) test. As far as fiber is concerned, for all practical reasons there is no EMI effect. STP or ScTP will provide some degree of RF protection if properly grounded on both ends which it never will due to ground loop concerns. It will not provide any degree of protection for low-frequency EMI because most of its energy is in magnetic component of the EM field and aluminum foils used in STP are transparent to magnetic fields. Coax cables are really for so different applications that I don't know why would you even throw them into the mix, but all the STP considerations apply here as well. Best Regards, Dmitri Abaimov, RCDD http://www.cabling-design.com/ Home Cabling Guide, Cabling Forum, color codes, pinouts and other useful resources for premises cabling users and pros -- ##-----------------------------------------------## Article posted with Cabling-Design.com Newsgroup Archive http://www.cabling-design.com/forums no-spam Web and RSS interface to your favorite newsgroup - comp.dcom.cabling - 2650 messages and counting! ##-----------------------------------------------## | |||||||||||||||||||||||||||||||||||||
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Posted by Al Dykes on June 26, 2006, 8:13 pm
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>Ralf Koenig wrote:
> > >> I'm looking for a comparison that quantifies the effects of EMI
>> (electro-magnetic interference) on the following media: >
>> UTP (Cat.3, Cat.5, Cat.7)
>> STP (Cat.3, Cat.5, Cat.7) >> Coax RG-58 and RG-59 >> Fiber Optics >
>> There are many qualitative statements on the web, that say that EMI
>> sensitivty decreases when going down the list mentioned above (in other >> words: UTP is most prone to EM interference, fiber is least or not at >> all prone to EM interference). >
>I doubt you will find many reliable references let alone numbers. A test >like that is extremely hard to produce and maybe harder yet to verify. >Also, cabling manufactures are rarely if ever have access to equipment and >facilities required to conduct such tests, especially RF. I have seen >tests done (even took part in one many years ago) but the results were >very dependent on the environment the tests were conducted in. > >The one I've assisted to conduct was strictly RF, so I would not >necessarily project the results onto low frequency noise from likes of >power cables and fluorescent lamp ballasts. However, for RF it boils down >to this: before your UTP (CAT5E and CAT6 - have not seen this done to >CAT3) cable will pick up enough noise your equipment -PC and pretty much >everything else - will fail (and people flee ;-)) because you are talking >way beyond FCC and EC allowed levels. You will never encounter such high >levels of EM fields in commercial and residential environments so there is >really no need to worry about the cable. Let me re-phrase that: worry >about the electronics before worrying about the cable. > >If you are in a special environment (industrial, science lab, ship, plane, >spaceship etc.) - you are on your own. Feel free to conduct your own tests >and come up with your own results - no cable manufacturers will ever >guarantee anything or even conduct such (very expensive to setup) test. > The EMI issue began when Ethernet over UTP was really new and I've never known it to be anything but theoritical. I don't even recall "CAT3" as a specification when I first put Cabletron hubs in service. At the time somebody did some practial test, wrapping loops of what we would call CAT3 cable around zerox machines,arc welders, small power tools, etc, while running BERT tests. As I recall, the BERT error level was ZERO. I don't think I've ever heard of EMI-induced errors in commercial use of UTP. If I were installing a network near an MRI machine or near an electric arc furnace I'd use fibre, but I'd have lots of other issues, too. Even if there were an occasional noise shot, A TCP/IP network would resend the packet very nicely, thank you. UTP cable is twisted pairs of wire. One byproduct of that is that any external EM field that would induce voltage in one wire induces an identical, opposite voltage in the other wire of the pair. They cancel out. For perfectly symetrical pairs EMI induces zero net voltage. As I understand things, UTP wire, in each step from CAT3 to CAT 6 has improved the exactness of the twists. This makes CAT6 much more EMI-resistant than CAT3, especially what was in use when the tests I recall were done. -- a d y k e s @ p a n i x . c o m Don't blame me. I voted for Gore. A Proud signature since 2001 | |||||||||||||||||||||||||||||||||||||
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Posted by Robert Redelmeier on June 27, 2006, 9:11 am
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> As I understand things, UTP wire, in each step from CAT3 to
> CAT 6 has improved the exactness of the twists. This makes > CAT6 much more EMI-resistant than CAT3, especially what > was in use when the tests I recall were done. AFAICS, Cat3 to Cat5 was an improvment in EMI (all twists much tighter), but since then, most of the improvements have been to reduce crosstalk (twists slewed). I think Cat5/5e/6 are all pretty much the same for external EMI, although some of the siamesed-pairs might be slightly better. -- Robert | |||||||||||||||||||||||||||||||||||||
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Posted by David Lesher on June 28, 2006, 9:20 am
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Neither Coax or UTP is sensitive to EMI. Their terminating electronics, may be, however. That's a function of many factors, none easy to generalize about. -- A host is a host from coast to coast.................wb8foz@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 | |||||||||||||||||||||||||||||||||||||
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> (electro-magnetic interference) on the following media: