ANSI/IEEE 802.3 specifies 10Base2 earthing at some point along the cable, but not at any node. 10Base2 nodes typically are an isolated (DC/DC + level shifter) 9-volt part of the PBWA with a high resistance connection to chassis.
[RF radiation is higher and RF immunity is lower than 10BaseT. The 'shield' is a conductor so it radiates if not earthed.] To reduce emissions ground the cable at a single point (typical office installations had punch blocks in the wiring closet); additional points may introduce ground loops. Other replies suggest an AC ground...you need to eliminate odd-order harmonics (typically 5th to 13th). Also check COTS 10Base2 component specifications: some were only Class A. It is difficult dealing with legacy technology. Choices of COTS 10Base2 are limited, EMC modifications change it to 'custom.' David From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Wednesday, March 05, 2003 3:38 PM To: emc-p...@majordomo.ieee.org Subject: Ethernet coax connection Question for list members: Background: I am troubleshooting a complex integration of military hardware and COTS. One COTS piece of equipment has an RG-58 coaxial connection, but the coax connector is an isolated feedthrough bnc. From a radiated emissions point-of-view, that is hurting us. One of the engineers here said that is part of the spec - Ethernet shields are not supposed to be chassis grounded. Question: Can someone please explain the reason for that, and how this is usually handled to minimize radiated emissions? Thank you. Ken Javor EMC Compliance Huntsville, Alabama 256/650-5261 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
