Ken Javor wrote: >> My thinking is just the opposite. The duration of the pulse should be long relative to the time it takes to travel from transmit to receive antennas. Then there is no smearing <<
It seems to me that you may be overlooking the effect of the reflected wave on a received pulse's shape. Consider the step function, which is certainly longer than the time to propagate across a chamber. Won't its leading edge be reflected, and subtract from the pulse? Won't subsequent reflections either (momentarily) increase or decrease it? And, given an imperfectly symmetrical chamber, won't there be a confusing multitude of such reflections? Of course, half the reflected energy incident on the antenna would be re-radiated, and so on for each reflection, diminishing their effect with time, but still, there's distortion not compensated for by a long pulse. An analogy might what happens with a two dimensional cavity -- an unterminated transmission line -- when we send a fast rise-time pulse down it. We are not, I think, precisely in disagreement; I do agree a short pulse will be smeared (after some time). It's just that I think reliance on a longer one won't insure that it remains undistorted. If rise and fall times were longer than the chamber transit time, then I'd expect no problem. I've not studied the chamber/pulse problem, mind. I did -- almost 20 years ago -- set up two bicons a meter apart in a 4 meter long reverberant chamber, and look at site attenuation. Nulls over 40 dB; high Q, indeed! See the May issue of the Transactions on Antennas and Propagation for a similar look (with regard to antenna impedance) at "Statistical Properties of Linear Antenna Impedance in an Electrically Large Cavity.*" That may have some relevance to your query. Ad astra per aspirin. Cortland *Statistical Properties of Linear Antenna Impedance in an Electrically Large Cavity, L.K. Warne, K.S. H. Lee, H.G. Hudson, W.A. Johnson, R.E. Jorgenson, and S.L Stronach. Volume 51 Number 5, page 978. 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
