Hello Grace - I concur with Mark Briggs. Use of the FCC methods are by far the simplest methods and the most widely accepted.
Chas From: [email protected] [mailto:[email protected]] On Behalf Of Grace Lin Sent: Thursday, August 27, 2009 6:23 AM To: Michael Heckrotte Cc: Mark Briggs; [email protected]; [email protected] Subject: Re: Power Meter Good Morning Michael, Thank you so much for sharing your knowledge. I just realize the importance of video bandwidth of a power meter/sensor this week. I believe the models you listed represent the latest models from vendors, at least from R&S and Agilent according to my research this week. Last Thursday I visited Rohde & Schwarz's booth at the 2009 IEEE Symposium on EMC. A knowledgeable sales representative explains to me that a power meter is a display unit. A computer can achieve the same display function as a power meter. A group member confirms it. This will save the cost for a power meter. Could you please indicate the source of: "The diode detector and oscilloscope .... the FCC has explicitely stated that they will not accept this method." I found this combination (diode detector and oscilloscope) from a TCB certified application tested/issued by a well-known commercial laboratory. Best regards, Grace On 8/26/09, Michael Heckrotte <[email protected]> wrote: > Hi all, > > Not all peak power meters and sensors are created equal. The FCC requires > that the video bandwidth of a peak power sensor/meter be greater than or > equal to the RF bandwidth of the signal being measured. > > To the best of my knowledge there is only one Rohde & Schwarz sensor that is > acceptable for 802.11 devices. This is the NRP power meter with the NRP-Z81 > sensor, which has a video bandwidth of 30 MHz. Thus it can only be used to > measure 20 MHz WLAN transmissions. The peak sensors in the NRV-Z series are > only suitable to measure the peak power of TDMA cellular phone signals. > > Agilent has a 30 MHz video bandwidth sensor in their P-series power meters > with P-series wideband power sensors. > > Anritsu has a 39 MHz video bandwidth with a 2490 series meter and MA2411B > sensor. > > Boonton has a 50 MHz / 65 MHz video bandwidth with a 4500B meter and a 58318 > / 56006 sensor, respectively. They have a 35 MHz video bandwidth with a 4400 > or 45xx series meter and 573xx sensor. > > Some or all of these vendors may have newer products since I last did > research into this area. > > The diode detector and oscilloscope is specified by various ETSI standards, > but the FCC has explicitely stated that they will not accept this method. > Although this is theoretically a good way to measure peak power, I would > make a SWAG that the FCC's objection is based on verifying the video > bandwidth. > > Best Regards, > Mike > > Michael Heckrotte > Director of Engineering > > Compliance Certification Services > 47173 Benicia Street, > Fremont, CA 94538 > > Main: (510) 771-1000 > Direct: (510) 771-1121 > Fax: (510) 661-0885 > > [email protected] > > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of Mark Briggs > Sent: Wednesday, August 26, 2009 9:49 AM > To: 'Grace Lin'; [email protected] > Subject: RE: Power Meter > > Grace - > > Do you have a problem using the FCC's methods of measuring the output power > with a spectrum analyzer (for peak power you would use method 3 in the FCC > procedure outlined in their document DA 02-2138 - the method that uses max > hold)? > > Typically for 802.11 devices you are stuck with FCC method 1 (if the device > transmits continuously or your analyzer can be gated to only sweep when the > device transmits) or FCC method 3 (if device does not transmit continuously > and the analyzer gating does not work). Method 3 will give you a higher > value (by as much as 8dB) than method 1 for the same device because it is > measuring peak power and not average power. > > If you are not going to use one of the three methods (that use the analyzer > to make the power measurement) then you would need to measure the peak > power. I have used a R&S Peak power sensor (envelope power) and the results > compared favourably to the method 3 results. An alternative would be to > use a diode detector and o'scope to determine the peak power based on the > maximum voltage recorded by the diode detector. > > Feel free to look at this paper that compares measurements using method #3, > an average power sensor, a peak power sensor and a diode detector: > http://www.elliottlabs.com/documents/OFDM.pdf, but what is missing is the > use of FCC method #1 (which would give results similar to the average power > sensor). > > Good luck, > > > Mark > ________________________________________ > From: [email protected] [mailto:[email protected]] On Behalf Of Grace Lin > Sent: Tuesday, August 25, 2009 5:02 AM > To: [email protected] > Subject: Power Meter > > Dear Members, > > I am in an urgent need for a power meter and would like to hear your > comments. My purpose is to measure peak output power per FCC 15.247 and > 15.407 for IEEE 802.11 a/b/g/n devices. > > There are several vendors available on the market (Agilent, Anritsu, Booton, > Gigatronics, Rohde & Schwartz, etc.). Is there any particular vendor and > model you recommend? You may wish to reply it off-line. > > What is your comment on USB power sensors (eliminate a power meter and > connect to a PC)? Examples are Agilent > U200A http://www.home.agilent.com/agilent/product.jspx?cc=US&lc=eng&pageMode > =OV&pid=1079918&ct=PRODUCT&id=1079918 (measureing average power only) and > R&S NRP-Z81 > http://www2.rohde-schwarz.com/en/products/test_and_measurement/power_vol t_me > ter/power_meters/NRPZ81.html. Do USB power sensors have the same quality as > traditional power meters with sensors? > > Does "envelope power" refer to peak power? What is the diference between > "true average" and "average" power? > > Is there any instrument specification that I have to focus on? > > Thank you very much for your time and look forward to hearing from you. > > Best regards, > Grace Lin > - > ---------------------------------------------------------------- > 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]> > - 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]>
