>> The amplitude modulation increases the amplitude as well as decreasing it. Modulation 'depth' suggests, wrongly, that it only decreases.
Correct. However, it is probably worth noting that in automotive EMC testing, the maximum envelope excursion of the modulated signal is set equal to the maximum envelope excursion of the unmodulated signal. In this 'special' case, the modulation only decreases. Ref: 95/54/EC Appendix 4, ISO 11452-1 Annex B) Rgds - Chris Chileshe (OO Only) From: [email protected] [mailto:[email protected]] On Behalf Of John Woodgate Sent: 15 August 2007 22:07 To: [email protected] Subject: Re: field strength and modulation In message <[email protected]>, dated Wed, 15 Aug 2007, Ralph McDiarmid <[email protected]> writes: >I?ve been informed that a 20V/m field when modulated to depth of 80% >produces a 36V/m field strength. Would someone explain how that works. >I?m puzzled. The amplitude modulation increases the amplitude as well as decreasing it. Modulation 'depth' suggests, wrongly, that it only decreases. 80% of 20 V/m is 16 V/m, so the maximum field strength during the modulation cycle is 36 V/m, and the minimum is 4 V/m. Note that all these numbers, if they are in a diagram, are peak values, but since all the r.m.s. values are 1/sqrt(2) of the peak values, the same numbers are valid if the peak unmodulated field strength is 28.3 V/m. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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 [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - 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 [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
