Noise figure is BW independent. Noise floor is BW dependent. Ken Javor Phone: (256) 650-5261
________________________________ From: "ce-test, qualified testing bv - Gert Gremmen" <[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Wed, 26 May 2010 21:43:27 +0200 To: Ken Javor <[email protected]>, <[email protected]> Conversation: Radiated emission testing for automotive at low levels. Subject: RE: Radiated emission testing for automotive at low levels. Hi Ken, and Collegues Thanks for elaborating, Now I remember, you wrote that 50 dB of a noise figure F is “quite high”. I also understand that the noise figure F is BW dependent, so at 10 kHz it will be less. I read the Ed Price has respectable equipment having on average the same noise level at the same bandwidth so the same F. In what context should I read “quite high” then if at other bandwidths the noise figure is different. In what way can we judge the quality of a Spectrum analyser regarding noise then. Are there SA available with F = 30 dB at 120 kHz ? Is that only because a pre-amp with low noise figure and high gain will be build in ? Can you also say something about test receivers, if I understand well, the principles are identical for receivers also… Last question, I consider LNA experimenting with MiniCircuits pre-amps such as the Lee-39+ In evaluation kit. It is specified to 8 Gig, has a 2.5 noise figure, 20+ gain and 2 in series should do the job. 1st intercepts are + 10 dBm and costs 60 dollar build. If preamps for our purpose are expensive (10k+) and 2 of these cost 120 dollar, where is the trade off. I am not an LNA specialist , so I can use some tips… A lot of questions, but as usual, any answer creates more questions… Gert Gremmen Van: [email protected] [mailto:[email protected]] Namens Ken Javor Verzonden: woensdag 26 mei 2010 19:37 Aan: [email protected] Onderwerp: Re: Radiated emission testing for automotive at low levels. Noise floor (dBm) = -174 dBm + 10*log (BW) + F (dB) At room temperature, where F is noise figure. If F isn’t given, but a noise floor is given with a stated BW, then using the above equation, you can get the noise floor at any other BW using: Noise floor (dBm) = Noise floor at stated BW (dBm) + 10*log (BW desired/BW stated) Keep in mind, as someone else noted, that receiver manufacturers often state noise floor as “displayed average noise level.” That uses video averaging, which isn’t allowable if making a peak detection measurement. You can add about 12 dB for the difference between DANL vs. peak detection, other things (BW) equal. Ken Javor Phone: (256) 650-5261 ________________________________ From: "ce-test, qualified testing bv - Gert Gremmen" <[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Wed, 26 May 2010 13:24:43 +0200 To: <[email protected]> Conversation: Radiated emission testing for automotive at low levels. Subject: RE: Radiated emission testing for automotive at low levels. Hello Friends, Collegues, Thanks to all of you for help, comforting words en correcting some misconceptions on my side. My conclusions are: * Nothing wrong with my analyser, -71 dBm is quite normal * I need more gain and less losses into cabling (the latter had already my attention before with immunity testing) * More gain into more efficient antenna’s (= lower antenna factors) * More gain = Have a “better” pre-amp, instead of 24 dB, I might need 45 or 50 dB of gain and where possible, less noise * Limits have been over specified in some cases To illustrate this last point, manufacturer has come up with relaxed requirements after I mentioned that the noise exceeded the limit lines. As a last question: How can I predict the noise floor from the analysers specification (-154dBm at 10H Regards, Ing. Gert Gremmen [email protected] <mailto:[email protected]> <mailto:[email protected]> www.cetest.nl <www.cetest.nl> Kiotoweg 363 3047 BG Rotterdam T 31(0)104152426 F 31(0)104154953 Before printing, think about the environment. Van: [email protected] [mailto:[email protected]] Namens Cortland Richmond Verzonden: Wednesday, May 26, 2010 12:56 PM Aan: [email protected] Onderwerp: RE: Radiated emission testing for automotive at low levels. Good day, Gert. The straightforward answer is an antenna with enough gain to provide the margin needed for a valid test. Gain required can be reduced by using lower loss coax and up-front preamplification. Add 8 dB antenna gain, cut cable loss in half, and add a low-noise preamp with 10 dB gain at the antenna (or any equivalent combination). i have recently seen that done with good results. In a "previous life" I brought my 800-1000 MHz noise floor down with a much better coax cable, but that was for a 10 meter OATS. Then I had to either switch to the internal preselector or add attenuation because the "usual 8447D" was overloaded by ambients. My supervisor and co-workers were not comfortable with these measures, which didn't last long, however and that company no longer exists. But I digress. More gain, less loss. Cortland Richmond KA5S ----- Original Message ----- From: ce-test, qualified testing bv - Gert Gremmen <mailto:[email protected]> <mailto:[email protected]> To: [email protected] Sent: 5/25/2010 3:17:45 PM Subject: Radiated emission testing for automotive at low levels. Colleagues and friends, I have recently been asked to quote testing for automotive car manufacturers ESA specifications. Part of the specification is very low level testing, as low as 20 dBuv/m at 120 Khz BW above 1 Gig. Can any of you shine their lights/contribute 2 cents on the test configuration needed for that. I have run into the following problem: Our R&S analyzer has a noise floor at 120 kHz bandwidth of approximately -71 dBm. Adding a 6 dB preamplifier noise and 24 dB gain lowers the noise floor to 89 dBm (18 dBuV). Our horn antenna (3115) has a AF of >20 dB (@1m) and the resulting noise level field strength is about >38 dBuV/m What is your choice in solving this problem ? Gert Gremmen - 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. 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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. 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