Reviewing MP-5, the test method for FCC Part 18, there is a great deal of flexibility on how to perform the average measurements. However, the measurement detector needs to be linear.
The phrase in clause 2.2.2 is, "For radio noise meters or spectrum analyzers which include weighting circuits, the detector function shall be linear." MP-5 specified that the SA needs to meet ANSI C63.2:1980. A review of the Spectrum Analyzer's specifications may indicate this. MP-5 is available at the FCC-OET website. If it is available, ANSI C63.2 would need to be purchased. My understanding is that reducing the VBW while keeping the RBW constant (in this case 1 MHz) and using a linear display will yield a true average measurement. An alternative to using an average detector, if the duty cycle of the emission is known, would be to apply an average factor to the peak measurement. This is explained in FCC Part 15.35. Review of MP-5 is necessary to determine whether or not the Spectrum Analyzer averaging function is adequate for the measurements. If not, the method used must be approved by the FCC or obtain a compliant average detector. Michael Peters From: [email protected] [mailto:[email protected]]On Behalf Of Ralph McDiarmid Sent: Tuesday, August 24, 2004 11:30 AM To: [email protected] Subject: RE: Average Detection That's my understanding as well. Ralph McDiarmid, AScT Compliance Engineering Group Xantrex Technology Inc. > -----Original Message----- > From: [email protected] [mailto:[email protected]] > Sent: August 24, 2004 8:07 AM > To: [email protected]; > [email protected]; [email protected] > Subject: RE: Average Detection > > > One of the earliest posts to this question (I have since deleted that > post) mentioned the incorrectness of averaging after the > logarithmic detector. Averaging after the log detector, I > believe, does not correctly average the signals. However, > this appears to be standard and accepted practice. Even the > common technique of averaging multiple signal measurements in > decibels, such as five different PC's, is not correct. The > technically correct method is to convert the measurements > into linear units, average them, then convert to decibels. > Any comments on this? > > Dave Cuthbert > Micron Technology > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Charles Grasso > Sent: Monday, August 23, 2004 7:38 PM > To: Ralph McDiarmid; [email protected] > Subject: RE: Average Detection > > > There is some variance as to the appropriate > VBW setting to make an accurate average measurement. > As I recall there is (and I have forgotten what it is) > a ratio that must be maintaied between the RBW and the VBw > settings. Our Spectrum Analyzer uses a 30Hz bandwidth setting > (for conducted emissions) but one lab mentioned that a 1kHz > VBw should be the minimum. > > Chas Grasso > > -----Original Message----- > From: [email protected] > [mailto:[email protected]]On Behalf Of Ralph McDiarmid > Sent: Monday, August 23, 2004 9:45 AM > To: '[email protected]' > Subject: RE: Average Detection > > > It's my understanding that the 10Hz VBW provides a filter > time-constant approximating that of an average detector. > > Ralph McDiarmid, AScT > Compliance Engineering Group > Xantrex Technology Inc. > > > > -----Original Message----- > > From: [email protected] > > [mailto:[email protected]] On Behalf Of Tom Cokenias > > Sent: August 23, 2004 6:51 AM > > To: Ridler, Samantha; '[email protected]' > > Subject: Re: Average Detection > > > > > > Hello Samantha, > > > > For analyzers that do not incorporate an average detector, > the FCC has > > specified settings of RBW 1 MHz and VBW of 10 Hz for average > > measurements in other parts of the Rules for measurements > above 1 GHz. > > They have been accepting these settings for many years for spread > > spectrum and now 802.11 radios operating under 15.247 of the Rules. > > > > best regards > > > > Tom Cokenias > > > > T.N. Cokenias Consulting > > P.O. Box 1086 > > El Granada CA 94018 > > > > tel 650 726 1263 > > fax 650 726 1252 > > > > cell 650 302 0887 > > > > At 8:21 AM +0100 8/23/04, Ridler, Samantha wrote: > > >Hello All > > > > > >FCC part 18 requires the use of an Average detector. For > > measurements > > >above 1GHz on a HP8593E EMC (Spectrum) analyser, would > > using a Video > > >Average of 100 or more be equivalent to taking a > measurement with an > > >Average detector? > > > > > > > > >It has been suggested to me by a test house that this is the > > case, but > > >I have not managed to find any rationale for this. > > > > > >The setup for the Analyser in question during the measurent was as > > >follows if this helps: SPAN = 2GHz, RBW =1MHz, VBW = 3MHz, > > SWEEP =40ms > > > > > >Many thanks. > > > > > >Samantha Ridler BEng MIEE > > >Compliance Engineer > > > > > >---------------------------------------------------------------- > > >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/listserv/request/user-guide.html > > > > > >List rules: http://www.ieee-pses.org/listrules.html > > > > > >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] > > > > > >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/listserv/request/user> -guide.html > > > > > > List rules: > > http://www.ieee-pses.org/listrules.html > > > > 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] > > > > 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/listserv/request/user> -guide.html > > > List rules: > http://www.ieee-pses.org/listrules.html > > 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] > > 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/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html 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] 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/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html 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] 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/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
