Ken, a few thoughts. Did you account for radiation resistance? You have described not merely a single-wire transmission line but ALSO, a fairly good antenna.
The impedance is probably higher than you calculate. A coax cable with the same ratio of shield radius (height above ground) to inner conductor size will be higher impedance tan your 15-25 ohms. You have greater spacing -- the ground isn't concentric -- and the impedance HAS to be higher. For all but the lowest frequencies in the range you mention, the chamber prevents current on the cable from flowing as on a transmission line; its resonances couple differently to the line than operating over an unenclosed ground plane. But assuming your matching is correct, you SHOULD see only a travelling wave on the cable, and current or voltage that does not vary along the line (except due to loss). If the match is incorrect, you will have standing waves, and this you can confirm pretty easily with a current probe. The chamber resonances may obscure this. It is possible to find loss in common mode simply by measuring common-mode current at a peak near one end of a suspended conductor and again at a peak near the other end. The location of current nodes will depend (outside a chamber!) on wavelength, but the difference between them over length will depend on radiation and other losses. 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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"
