I'll concur with Don, but as discussed at the IEEE 802.3z Gigabit Ethernet Task Force meeting in Irvine, California on March 10-14, 1997, this was apparently briefly discussed.
The full text is at http://grouper.ieee.org/groups/802/3/z/public/minutes/Irv0397.txt I quote only the important part <cough> ... "Cable shielding was discussed and it was explained that two shields are required to meet radiated emissions requirements. This configuration easily passes "Class B"." At another site, http://www.anixter.com/techlib/vendor/cabling/lan1000.htm it is "suggested/hinted/implied" that compliance either for emissions and/or especially with balance on UTPs, the burden of compliance rests not on thy humble standard when considering all possible applications. Compliance rests with thee. <strictly my own interpretation> Regards, Doug At 12:05 PM 12/7/98 -0800, Donald Kimball wrote: >The IEEE 802.3ab defines the new Gigabit Ethernet Standard (i.e. >1000Base-T). This Local Area Network (LAN) can use 4 twisted pairs of >unshielded copper cable (Category-5) at 100m maximum operating at 250Mb/s >per pair in full-duplex bi-directional mode. This standard is designed to >utilize existing LAN cables such as older 10Base-T and 100Base-T networks. >The signaling (i.e. baud) rate is 125MHz per pair using 5-level Pulse >Amplitude Modulation (PAM) . This probably results in the fundmental energy >at 62.5MHz given that the signal must be bipolar to be compatible with >transformers. Vendors such as Broadcom Corp. have developed single chip >copper cable interfaces for this new standard. > >In the past, standards using unshielded cables, such as 100Base-T, >10Base-T, T1, E1, etc, have had signaling rates less than 30MHz, so that >the fundamental frequency was below the 30MHz FCC and CISPR starting >frequency for radiated emissions. However, 1000Base-T has a 125MHz >signaling rate. A common mode current of less than 10uA at 30MHz at 1/2 of >wavelength can yield an emission level equal to or greater than the Class B >level. In addition, the 4 twisted pairs are all phase locked to each other. >The intentional differential mode current is about 10mA, so the trans >hybrid balance needs to be better than 60dB. This is achievable with the >hybrid at the component level, but not at the system level with 100m of Cat >5 cable attached. > >Conclusion, I think that 1000Base-T (IEEE 802.3ab) on unshielded Category >5 cable is doomed to fail EMI. Anybody ever try a test? Any other opinions? > >Don Kimball --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
