Ken, do you mean you pulse an antenna with a square wave at some specific repetition rate? If so, The pulse rise time and duration can be selected to contain the frequency components you want. I think that if the pulse remains on two long, the generator will act as a 50 ohm load and absorb energy from the chamber. Switching the generator from a 50 ohm state to a high-Z or low-Z state could be beneficial.
Dave Cuthbert Micron Technology From: John Woodgate [mailto:[email protected]] Sent: Sunday, July 27, 2003 11:53 AM To: [email protected] Subject: Re: pulse modulation in reverb chambers I read in !emc-pstc that Ken Javor <[email protected]> wrote (in <bb49768d.3717%[email protected]>) about 'pulse modulation in reverb chambers' on Sun, 27 Jul 2003: >So if I am worried whether the 1 us pulse width can be sustained, and I >don't know how to determine it analytically, my plan is as follows: > >I put a wire probe in the room, run it to a spectrum analyzer tuned to >the transmit frequency, put the analyzer in zero span mode with a 1 or 3 >MHz bandwidth and look at the modulation waveform. If it is >significantly longer than 1 us, I know my constructive interference path >delays are smearing the modulation away. I originally thought you wanted to establish a reverberant field with a 1 us pulse. Now I'm not so sure. By 'modulation', you mean the envelope of the 1 us pulse? Isn't the idea of a reverberation chamber that once it is excited the energy takes a long time to die away? That means that the original pulse will be s t r e t c h e d, dying away exponentially if the room is a good one. A too-short pule would almost certainly produce a delay that was not exponential. You can only 'sustain' the 1 us pulse if your receiver is in the 'direct field' of the antenna, i.e. the field strength due to the direct propagation path from sending antenna to receiving antenna is at least 3 dB above the combined field strength due to all indirect paths. You can easily see this if you consider just a few simple specular reflections, which appear at the receiver as a series of overlapping (since their path lengths are less than 300 m) 1 us pulses of varying level. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! 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 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
