RJ45 splitter for Ethernet - possible ?
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Posted by on March 28, 2008, 4:47 pm
Please log in for more thread options Since 10Base-T and 100Base-TX were both designed to coexist with phone lines in the same cable, that shouldn't be a problem. -Larry Jones Start tying the sheets together. We'll go out the window. -- Calvin | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by News Reader on March 28, 2008, 7:03 pm
Please log in for more thread options A telephone ringing signal is an 88v 20Hz A.C. signal superimposed on 48v nominal D.C. supervisory voltage. Hardly low voltage, and not appropriate for sharing a Cat 5e cable run with data. Readers should observe gfretwell's caution. Best Regards, News Reader lawrence.jones@siemens.com wrote: > gfretwell@aol.com wrote:
>> Don't do this with POTS phones unless you can live with the errors
>> when the phone rings. >
> Since 10Base-T and 100Base-TX were both designed to coexist with phone > lines in the same cable, that shouldn't be a problem. > > -Larry Jones > > Start tying the sheets together. We'll go out the window. -- Calvin | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by on March 28, 2008, 10:08 pm
Please log in for more thread options >
> Possible and advisable are two different things. Absolutely. > A telephone ringing signal is an 88v 20Hz A.C. signal superimposed on
> 48v nominal D.C. supervisory voltage. > > Hardly low voltage, and not appropriate for sharing a Cat 5e cable run > with data. The former is true, the latter is debatable. Cat5 cable is used for phone wiring, so the voltage is not a problem for it (in fact, most Cat5 cable is rated for 300V). The IEEE 802.3 spec for twisted pair ethernet requires devices to provide at least 1500V of isolation, so it's not a problem for the attached devices, either. And the baseband signal is up in the MHz range, so the receiver won't even see a 20Hz signal. Like I said, twisted pair ethernet was specifically designed to coexist with ordinary phone circuits in the same cable, although that's not recommended for structured wiring systems. -Larry Jones No one can prove I did that!! -- Calvin | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by News Reader on March 29, 2008, 12:00 pm
Please log in for more thread options The point is not whether the "cable" can withstand high voltage.
The point is that Ethernet is a low voltage, low current implementation. The issue is induction, and induction results from current, not voltage. If you think a high current, low frequency signal cannot impact the receiver, you are incorrect. If you were correct, we would not observe the minimum separation distances from EMI sources that we do, when installing network cabling. We keep data cabling away from AC wiring (i.e.: 60 Hz), and if we have to cross paths with AC, we ensure that we are perpendicular to the AC wiring, and never parallel to it, due to the effects of induction. Best Regards, News Reader lawrence.jones@siemens.com wrote: >> Possible and advisable are two different things.
>
> Absolutely. > >> A telephone ringing signal is an 88v 20Hz A.C. signal superimposed on
>> 48v nominal D.C. supervisory voltage. >> >> Hardly low voltage, and not appropriate for sharing a Cat 5e cable run >> with data. >
> The former is true, the latter is debatable. Cat5 cable is used for > phone wiring, so the voltage is not a problem for it (in fact, most Cat5 > cable is rated for 300V). The IEEE 802.3 spec for twisted pair ethernet > requires devices to provide at least 1500V of isolation, so it's not a > problem for the attached devices, either. And the baseband signal is up > in the MHz range, so the receiver won't even see a 20Hz signal. Like I > said, twisted pair ethernet was specifically designed to coexist with > ordinary phone circuits in the same cable, although that's not > recommended for structured wiring systems. > > -Larry Jones > > No one can prove I did that!! -- Calvin | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Robert Redelmeier on March 29, 2008, 2:01 pm
Please log in for more thread options > If you think a high current, low frequency signal cannot
> impact the receiver, you are incorrect. Well, technically ULF is seen at the receiver, but it is too slow and neutralized by balanced signalling to make any difference in the detection process. > If you were correct, we would not observe the minimum
> separation distances from EMI sources that we do, when > installing network cabling. There are many other reasons for separation. First and foremost is the dreaded electrical inspector who will often insist upon it (for electrical "safety") and her word is law. Second, some AC loads get very HF noisy (arc welders, certain motors and X-ray machines are frequently cited) and inject high freq noise onto AC. This noise can be troublesome. > We keep data cabling away from AC wiring (i.e.: 60 Hz), and
> if we have to cross paths with AC, we ensure that we are > perpendicular to the AC wiring, and never parallel to it, > due to the effects of induction. A clean AC draw (incandescent lighting) may produce some 60 Hz induction, but it is harmless and easily rejected by the receiver. Similarly the telephone ring 88V, 20Hz, unless you have an antique phone with contacts on the bell armature. Even then the protocols are robust and will retransmit. > Best Regards, News Reader
Please refrain from top-posting. The convention is quote-and-respond which makes following threads and side-comments easier. -- Robert | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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> Don't do this with POTS phones unless you can live with the errors
> when the phone rings.