The EM radiation from wires with and without ferrite cores can be simulated with NEC. The required parameters are: length of wire, physical orientation, how the end is terminated (floating? To ground?, frequency, the RL model of the ferrite). Then one can move the ferrite around to see what happens. There are situations where a single ferrite does virtually nothing. This why I am wary of just throwing on a ferrite and calling it good (although I have been known to do this). The complex impedance of a ferrite can be measured on a VNA. If a VNA isn't available an RF source, and a spectrum analyzer will give the scalar impedance. Or lately I have used a pulse generator and an oscilloscope to characterize ferrites for the design of wide-band time domain transmission line transformers. And I have used an MFJ-259B (only $260) to measure ferrites from 1.7 to 170 MHz.
Dave Cuthbert Micron Technology From: Chris Maxwell [mailto:[email protected]] Sent: Wednesday, January 29, 2003 11:57 AM To: Pettit, Ghery; [email protected]; [email protected] Subject: RE: EN55022:1998 + A1:2000 Ghery, If the standard is assuming a 50 Ohm system, doesn't this breakdown to a simple calculation? Insertion Loss = IL = 20 x log((50 + Zf) / 50)----where Zf is the ferrite impedance This could easily be solved for Zf if you assume IL to be 15dB (in this case the dB are truely dimensionless; as you are calculating a pure loss >from an arbitrary level). I would think that you would just have to: 1. Solve the above for Zf. By the way, I get 231.2 Ohms. Can someone check this? 2. Gather up a box of "doughnuts" such that the total Zf is above the answer for step 1 at all frequencies from 30Mhz to 1Ghz 3. Color code the doughnuts (or whatever) and write a procedure that says something like "clamp three blue doughnuts and two red doughnuts over each cable ..." Have I over simplified this??? Wouldn't this be proof enough for any accreditation body? I know that $300 may not seem like alot to some; but it adds up after a few cables. Besides; we went to college to learn all of that math; why not use some of it? I don't mind paying for stuff that I can't make; but this one seems possible to me. Chris Maxwell | Design Engineer - Optical Division email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | > -----Original Message----- > From: Pettit, Ghery [SMTP:[email protected]] > Sent: Wednesday, January 29, 2003 11:59 AM > To: '[email protected]'; [email protected] > Subject: RE: EN55022:1998 + A1:2000 > > > Amendment 1 to CISPR 22:1997 (Amendment A1:2000 to EN 55022:1998) requires > that the clamps provide at least 15 dB of loss in a 50 ohm system over the > frequency range of 30 MHz to 1000 MHz. The use of extension cords is > prohibited. Can you guarantee that your bucket of doughnuts will meet this > requirement? How will you demonstrate that to your lab's accrediting body? > > > Fischer's clamps are around $300 each. Compared with what we had to choose > from prior to their product, these are not big bucks. > > Ghery Pettit > Intel > > > > 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
