Derek, That is a very good carrot to nibble on!!
> 1) The test environment attempts the reproduce > consistent results. It may not > correlate with real fields encountered in use. So, > there is controversy on > how a test should run. Great point. From what I understand, plane waves are rarely encountered in the real world. At least that is what the companies selling reverb chambers will tell you. :-) And I tend to believe them. > 3) Assuming that we are stepping between > frequencies, what process is > followed? and what actually happens? In a good > chamber, with a 1% step, the jump in > level may not be significant. But, there will be > regions where the jump is > significant. In a system driving hard, the control > loop may not be linear, and the > predictive field level may be substantially higher > than actually needed: > essentially this is overshoot. Manually, overshoot > rarely occurs. Step sizes > greater than 1% exacerbate this problem. Very true. My experience is that at the lower frequencies, the frequency response of the total setup is pretty smooth, but once you get above about 200 MHz, and particularly as you approach 1 GHz, the required output level of the sig-gen may jump several dB from one frequency to the next. If the software always switches the same way (freq then level, or level then freq) then you are likely to have an overshoot that is entirely caused by the software. I have seen it happen. > Should the field level be reduced before changing > frequency? if so, how much, > and over what duration? > > Should the field be killed between frequencies? > > Some standards address this, some do not... I've seen some automotive standards that specify dropping 20dB between frequencies, and stepping up to the required level. Some also require an on/off test at each frequency as well. This really works the stepping attenuators!!! In my opinion, the frequencies tested should be the same frequencies that were calibrated. That is not a problem except for testing "EUT sensitive frequencies" which are never known at the time of calibration, so interpolation must be performed. IMHO, the best way to do that is to interpolate forward power and not sig-gen level, since the frequency response of the amp comes into play. Also, 1% steps are too large for the higher frequencies, 0.5 or even 0.25% may be needed. Cheers, Bob Richards, NCT. 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 emc-p...@ieee.org Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org 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://www.ieeecommunities.org/emc-pstc
