That is the same sort effect I've seen. Last time I bought some of the fist size ferrites they were $32 each.
Attitude is Mind over Matter. If you don't Mind, it doesn't Matter... This email has been displayed using 100% recycled electrons and 100% pure virgin photons. --- On Sun, 2/13/11, Derek Walton <[email protected]> wrote: From: Derek Walton <[email protected]> Subject: Re: [PSES] OATS vs anechoic To: [email protected], [email protected] Cc: [email protected] Date: Sunday, February 13, 2011, 9:04 AM HI Brian, a number of things can be going on. Just for a start, the chambers and OATS have NSA done, if your problems are vertical, it's possible to have 8 dB difference in NSA especially at the lower end: just keep that in mind. HOWEVER, NSA doesn't always reflect what the EUT does on the site. An observation I made testing a pump a while back was that the impedance of the power cord as it "terminates" at the shield room/OATS ground plane influenced greatly the radiated emissions. What I mean by terminates is that power under the ground plane may have filters, LISN's or nothing. BUT, the impedance there is going to influence the emissions. In my experiment I added several large Ferrites ( almost the size of a fist, just as the power came into the chamber from the Power line filters. There is nothing in the standards that says what the impedance of the power source should be for RE, so I believe this is legitimate. At 70 MHz emissions dropped almost 12 dB. The way you describe outages in bands kind of implies that a cable is resonating when you have excessive emissions, maybe the beads are worth a try... Cheers, Derek. -----Original Message----- From: Brian O'Connell <[email protected]> To: 'Brent G DeWitt' <[email protected]> Cc: [email protected] Sent: Sat, Feb 12, 2011 6:02 pm Subject: RE: [PSES] OATS vs anechoic Brent, The power cord is dressed casual. Sorry. Class II construction - no ground wire, hence no ground plane to reference. Back at the office and am now viewing similar dissimilar results from two indoor and two outdoor sites, so it probably has something to do with the H-field, and the power cord radiator makes a little more sense to me, I think... Brian > -----Original Message----- > From: Brent G DeWitt > Sent: Saturday, February 12, 2011 3:53 PM > To: [email protected] <http: /us.mc396.mail.yahoo.com/mc/[email protected]> > Subject: RE: [PSES] OATS vs anechoic > > > Hi again Brian, > > How is the power cord dressed and terminated at the ground > plane? Huge > variations between test sites on how this is done! > > Brent > > > -----Original Message----- > > From: Brian O'Connell [mailto:[email protected] <http://us.mc396.mail.yahoo.com/mc/[email protected]&;> ] > > Sent: Saturday, February 12, 2011 6:22 PM > > To: [email protected] <h tp://us.mc396.mail.yahoo.com/mc/[email protected]> > > Subject: Re: [PSES] OATS vs anechoic > > > > Just finished 2d OATS site - was not able to detect much > of anything. > > > > Went back to indoors fully anechoic, where the noise plot > is deafening. > > > > This is a simple 100W unit with one main ac/dc converter and (6) dc > > current modulators. Construction is mostly plastic, with > exception of > > metal base plate. As it is Class II construction, there is > no ground > > wire. > > > > Bad stuff is at 40-80MHz and 200-500MHz. Did some isolation > > troubleshooting - looks like the input power cord is the > main radiator. > > > > The EMC engineers at all three sites are both baffled and > fascinated > > and want a sample unit to play with. I am very happy that they are > > amused, but I have to ship a product and cannot afford to > support the > > Southern California EMC industry. > > > > thanks, > > Brian > > > > > -----Original Message----- > > > From: [email protected] <http: /us.mc396.mail.yahoo.com/mc/[email protected]> [mailto:[email protected]]On <http://us mc396.mail.yahoo.com/mc/[email protected]]On&> > Behalf Of Brian > > > O'Connell > > > Sent: Saturday, February 12, 2011 12:25 PM > > > To: [email protected] <http://us.mc396.mail.yahoo.com/mc/[email protected]> > > > Subject: OATS vs anechoic > > > > > > > > > Good People, > > > > > > Have tested at several sites. All are 'big' names and have a > > > good reputation. > > > > > > The 10m fully anechoic chamber data indicates from +5dB to > > > +11dB in several frequencies; while the 10m OATS says the > > > unit passes Class B, min -4.2dB. > > > > > > Huh?!? What is the physics behind the difference between an > > > outside site and absorbers? Where are the Borg when you > need them? > > > > > > Brian - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected] <http://us.mc396.ma l.yahoo.com/mc/[email protected]> > All emc-pstc postings are archived and searchable on the web at: http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected] <http://us.mc396.mail.yahoo.com/mc/[email protected]> > Mike Cantwell <[email protected] <htt ://us.mc396.mail.yahoo.com/mc/[email protected]> > For policy questions, send mail to: Jim Bacher: <[email protected] <http: /us.mc396.mail.yahoo.com/mc/[email protected]> > David Heald: <[email protected] <http:/ us.mc396.mail.yahoo.com/mc/[email protected]> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
