Hi, The length of the cable is one factor that determines the level of coupled signal presented to the EUT. EUT impedance is another factor.
Take a look at the operation of an active broad-band antenna as used in military EMC testing - I am thinking of the Singer - Ailtech design. It is a 39 inch rod, fed into a high impedance / low capacitance amplifier. Fields from 10kHz to 30MHz are received equally well - the response is flat with an antenna factor of 8dB. If the rod is extended to 41 inches and the capacitor hat is added (8 inch disk on top of the rod) the antenna factor becomes 0dB. The sensitivity of the EUT is whatever it may be - that is what is being tested. The level of pick-up at the EUT depends on the EUT loading of the wire, the length of the wire, the effective screening of the wire (if any) the field and the orientation of the wire to that field. If the EUT looks like a high impedance low capacitance input and the wire is orientated for maximum coupling - we could be talking about levels of approx. 500mV/volt of field up to maybe 1V/ volt of field. If the EUT looks low impedance, then there will be a ratio'd voltage presented of Zeut/(Zeut+Zwire) - whether this is significant in terms of interference depends on the design of the EUT in withstanding the applied voltage. No voltage, picked up on the cable and delivered to the EUT, is insignificant if the EUT can't stand that level. I hope this makes sense. Regards Tim 6239 desk A1S77 P Please consider the environment before printing this email. ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
