George, The physics of this is quite understandable. If you have a piece of electronic gear that emits radiation, it will also receive radiation with similar efficiency. If you provide the AC short to chassis ground that the BNC capacitor provides, then not only is internal radiation shunted to chassis and prevented from getting outside the chassis, but external radiation is also shunted to chassis which makes it more difficult for it to penetrate into the sensitive internal regions of the electronic system.
Bonding all the shields to ground is an eminently practical solution, but you produce a "custom" system, as another poster noted, rather than a 10Base2 system. 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 jim.knigh...@ncr.com -----Original Message----- From: Georg M. Dancau [mailto:g.m.dan...@dancau.de] Sent: Sunday, March 09, 2003 1:16 PM To: Ken Javor; emc-p...@majordomo.ieee.org Subject: Re: Ethernet coax connection Hi Group, I watched this interesting thread and noticed that none of you recalled the susceptibility of the system. We had severe problems with susceptibility of computers with Ethernet coax connection. As a matter of fact did not find any computer meeting the requirements for industrial environment of the 61000-4-4 (burst). They all failed at levels of a couple of hundred volts. Using capacitor coupled BNCs helps a bit. We simply bonded the shield to ground. I have to notice, that all computers attached to the network were in the same floor of the same building. Best regards George ************************************************************** * Dr. Georg M. Dancau * HAUNI MASCHINENBAU AG * * g.m.dan...@ieee.org * Manager Product Development * * TEL: +49 40 7250 2102 * K.A.Koerber Chaussee 8..32 * * FAX: +49 40 7250 3801 * 21033 Hamburg, Germany * ************************************************************** * home: Tel: +49 4122 99453 * Hauptstr. 60a * * Fax: +49 4122 99454 * 25492 Heist, Germany * * Cellular: +49 175 5805280* * ************************************************************** From: "Ken Javor" <ken.ja...@emccompliance.com> To: "Stone, Richard A (Richard)" <rsto...@lucent.com>; "'Knighten, Jim L'" <jk100...@teradata-ncr.com>; <emc-p...@majordomo.ieee.org> Sent: Wednesday, March 05, 2003 11:10 PM Subject: Re: Ethernet coax connection > > Thanks to all who answered in MINUTES assisting an EMI troubleshoot on > something that is of great national value. > > This forum is a tremendous resource! > > > > > on 3/5/03 4:46 PM, Stone, Richard A (Richard) at rsto...@lucent.com wrote: > > > we've had good success with the > > built capacitance of 9000pf as well, > > depending on test being discussed and > > frequency, certain cap. values from the shielded > > ring of the UNgrounded ring to earth works well > > for low freq..< 30 mhz. > > Richard, > > -----Original Message----- > > From: Knighten, Jim L [mailto:jk100...@teradata-ncr.com] > > Sent: Wednesday, March 05, 2003 4:12 PM > > To: Ken Javor; emc-p...@majordomo.ieee.org > > Subject: RE: Ethernet coax connection > > > > > > > > Ken, > > > > It is a potential shock hazard if the coax run is long and runs from > > building to building (for instance) where the ground potentials may be > > different in the different buildings. One can develop a large potential on > > the shield of the cable, so that if you put yourself between the cable > > shield and ground you may get a strong shock. That is the reason for > > isolating the shield from more than one direct connection to ground. It is > > a real issue. The result for EMI is, as you have noted, the creation of an > > egregious EMI offender. I have used the chassis mounted BNC connectors with > > built-in capacitors successfully. > > > > 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 > > jim.knigh...@ncr.com > > > > -----Original Message----- > > From: Ken Javor [mailto:ken.ja...@emccompliance.com] > > Sent: Wednesday, March 05, 2003 12:58 PM > > To: Knighten, Jim L; emc-p...@majordomo.ieee.org > > Subject: Re: Ethernet coax connection > > > > Assume complete ignorance on my part. What is the safety concern? > > > > > > on 3/5/03 3:50 PM, Knighten, Jim L at jk100...@teradata-ncr.com wrote: > > > >> Ken, > >> > >> Safety considerations are the reason for the spec requirement. You are > >> allowed to ground the shield at one point. > >> > >> Try using a BNC coax connector with a built-in capacitor to ground. That > >> gives you an AC connection to ground and is often quite effective. These > >> are off-the-shelf parts. > >> > >> 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 > >> jim.knigh...@ncr.com > >> > >> -----Original Message----- > >> From: Ken Javor [mailto:ken.ja...@emccompliance.com] > >> Sent: Wednesday, March 05, 2003 12:38 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 > >> > > -- > > 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 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
