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] 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/e /products/test_and_measurement/power_volt_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]>
