I've recently noticed modulation set too during RF immunity testing. It seems the sig-gen's were set to 80 percent AM, and the external audio signal set per the sig-gen manuals to what operators believed would be 80 percent. However, there was noticeable negative peak clipping and checking showed that indeed, the external modulating signal had to be reduced to get the requisite 80 percent modulation. Related issue: Function generators may if used for external modulating signals include a DC offset, which can and will cause negative peak clipping all by itself, too, so look out for that as well.
I'd encourage everyone to make a quick zero-span, linear mode SA modulation check part of routine calibration checks. Caveat modulator. Cortland Richmond 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: Ron Pickard: emc-p...@hypercom.com Scott Douglas emcp...@ptcnh.net 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
