Ken Javor wrote: >> My way of thinking about this problem and others like it is to reduce it to the simplest possible problem, and then look at the general case as a linear extrapolation. In this case I look at the interaction of the direct and single bounced ray during a site attenuation measurement on a perfect OATS, and then extrapolate from that to the reverberant chamber via linear superposition. I say this by way of an attempt to establish a common point of reference to enhance mutual understanding. <<
I too have thought about an OATS as a simplification. I think here I prefer an unterminated transmission line. Supporting multiple reflections, it is (unlike an OATS and similarly to a chamber) a resonator as well as a reflector. >> If the time delay between arrival of direct and bounced ray is much shorter than the pulse duration, then there is interference but insignificant spread or smearing. If the delay is a sizable fraction of the pulse duration, the received pulse will appear longer than the transmitted pulse. This is multi-path interference. If the time delay is well in excess of the pulse duration (but shorter than the pulse repetition period), then there is no constructive/destructive interference effect, but a second pulse appears at the receive antenna. << That is essentially my understanding; a really short pulse is received once undistorted. A longer pulse, however, could be lengthened, how much depending on pulse length, chamber size and Q. >> In the general case of a reverberant chamber pulse spreading would be contained if the difference between the shortest and longest paths of commensurate power density were equal to or less than 30 meters. << One needs to insure there are few enough reflections to keep this true, no? My one-meter experiment suggested that around 50 MHz, absorption was quite low; 50 dB cancellation implies that less than that was absorbed in the chamber walls. What can one expect at 1 GHz? Skin depth being less, surface resistivity would increase losses and reflections would be attenuated more quickly. How long do reflections actually remain a problem? Wish I could repeat the experiment, but I don't have access to a chamber just now. 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.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
