Ken, It depends if compliance with the Ethernet standard is important to you. If you connect to anyone else's network where someone else may be dealing with a coax that is grounded on your end, then it is probably important. If not, then it may not matter. This is a product safety issue. I have used 10BaseT (10 Megabit twisted pair Ethernet) in which we shield on both ends within our system. Whatever goes out to the world is not grounded on either end.
I am assuming from your messages that this may be a military system, so the product safety rules may be different than for commercial equipment. Jim Jim Knighten, Ph.D. Teradata, a Division of NCR http://www.ncr.com 17095 Via Del Campo San Diego, CA 92127 USA Tel: 858-485-2537 Fax: 858-485-3788 [email protected] -----Original Message----- From: Ken Javor [mailto:[email protected]] Sent: Wednesday, March 05, 2003 1:09 PM To: Robert Macy; [email protected] Subject: Re: Ethernet coax connection If all the ac equipment is powered by the same local source, and all the ac powered equipment is case-grounded within the same rack, is it correct to assume that the safety issue is moot? That is, can I then use a grounded bnc connector at both ends? on 3/5/03 4:02 PM, Robert Macy at [email protected] wrote: > It is my understanding there is a spec relating to both the voltage handling > capability and the impedance between ethernet coax and earth ground. > > At low frequency (must be more than a certain level) it is quite high in > order to prevent potentially damaging ground loops from forming. At high > frequency (must be less than a certain level) to effectively reference the > shield to chassis potential and make certain that the coax doesn't radiate. > > There are manufacturers that sell coax panel connectors with the "proper" > built in capacitor. I recall $10 each price tag. > > I further recall that we used to use 0.001uF 2kV caps. WELL DRESSED AND > MOUNTED EXTREMELY PROPERLY. > > Vaguely remember that the impedance was to be more than 1Meg at 60Hz and > less than 50 at 3MHz, but you should check the ethernet spec. > > You can tell a lot about the cap's mounting (and quality) by looking at the > spectrum of the radiated emissions. For example, internal clock and the cap > is referenced to a noisy spot. Or, spectrum related to the ethernet traffic > and a loop exists around the coax terminations and bypass cap. > > - Robert - > > Robert A. Macy, PE [email protected] > 408 286 3985 fx 408 297 9121 > AJM International Electronics Consultants > 101 E San Fernando, Suite 402 > San Jose, CA 95112 > > > ----- Original Message ----- > From: "Ken Javor" <[email protected]> > To: <[email protected]> > Sent: Wednesday, March 05, 2003 12:37 PM > 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 >> > > -- 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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
