Charles Grasso asked, >> I have a requirement to test the performance of ferrite bead (one that that can fit over a power cord) to 500MHz for qualification of alternate vendors. I have an impedance analyser - but it only goes to 40MHz. Does anyone have a good way to verify ferrite impedance.?? <<
A very quick way to compare beads is to observe attenuation through a single wire over ground plane with and without beads, using a SA and tracking generator. Or feed the power cord in common-mode from a signal source -- even a comb generator -- and look at the current with a probe, using different beads. This of course does not tell you the impedance of beads, only attenuation in the fixture, or one the cord, but may be enough. I'll note here that the RF CM impedance of power cords *in use* can't be predicted. They might be coiled, bundled, routed close to or away from other cables, alongside shields or other EMI sources... and a few cm difference can make hash of any calculations of ferrite effectiveness based on X and R figures. Are we asking for one percent specs for a ten percent result? Cheers, Cortland This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
