Just to add to what has already been said. Any reasonably sized transmit antenna gets very inefficient below 80 MHz at the desired distance of 3m. Sometimes the antenna has to be moved closer to reduce the power, but then you start getting into the near field. As mentioned previously, the lower frequencies are conducted in by the cables, so the conducted immunity standard covers those frequencies and are more repeatable since cable placement/routing is less of an issue. Mitigation also becomes easier with conducted immunity since the offending cable is more easily recognized. The preferred emissions measurement distance for most standards is 10m, so the frequency range can be extended lower before near field becomes an issue. The antenna efficiency for emissions is less of an issue, besides the fact that the corrected noise floor will be a little higher due to the antenna factors being poor. However, that is factored into the measurement and a pre-amp can be used to help there. As for the reciprocity of emissions vs immunity, I don't think we want to have to scan the antenna height from 1 to 4 meters during an immunity test. :-) Bob Richards.
--- On Tue, 3/9/10, [email protected] <[email protected]> wrote: Can someone tell me why the Radiated Immunity testing is conducted from 80 Mhz to 2 Ghz while Radiated Emissions is conducted from 30 Mhz to 1 Ghz (or 5th harmonic), i.e. why the gap from 30 Mhz to 80 Mhz for Immunity? Robert Hanson - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
