Lisa, On the expensive end, Noise-Ken has been at Symposia (which I can't afford this year) with a sniffer. It apparently uses four or five broadly tuned peak detectors and gives a bar-graph display for each band as its sensor is brought near the EUT. But, like others, I've found that a spectrum analyzer set on a broad sweep through the frequencies of interest works quite well, and it does nor have to be up-to-date, either. You can get an 8590 (for example) for relatively little, now, or a 7L13 and 7000 series mainframe, or a 141T with plug ins. Folks holding them are selling off excess gear now for badly needed funds. As for sensors, you do not need to spend money calibrating them, and this means you don' have to pay a lot for having them made. You can use throwaways.
For E-fields, a small piece of printed circuit board, or even just the coax center conductor wire, with a 50 ohm load across it, is sufficiently sensitive to find leaks, and ignore ambients and lower-level emissions. Even a scope probe works for this, but the tip needs to be insulated so you don't mess up results by scraping it across metal. For H-fields, you can wind a one-turn shielded loop by turning a coax back on itself, connecting the center conductor to the shield. I've made loops as small as 2mm across for following emissions on traces; bigger ones are useful for bigger problems. For current, you DO have a current probe - but even if you don't, a snap-on EMI bead with a one turn secondary connected to a piece of coax (the same shielded loop technique also works here) is a good, broadband sniffer for wires. And finally, if you know the frequencies of interest, you can now get pocket receivers which themselves are wonderful sniffers. A Vertex-Standard (formerly Yaesu) VR500 receiver, .1-1300 MHz (less cellular and 620-624) even has a spectrum occupancy function -- I can't quite call it a spectrum analyzer -- good for plus and minus 3 MHz. A lesser Yaesu radio, the VR120, with no such function, covering .5 to 1300 (with MORE unfortunate omissions of coverage), is presently on sale at Ham Radio and scanner radio stores for $99. (Receivers with NO omissions in coverage may be obtained from Canada and Europe.) Maybe next year I'll present a paper on using these erstwhile toys for serious EMI work. The economy willing! Good luck, Cortland ------------------------------------------- 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] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
