The fundamental equation from statistical thermodynamics is: N = kTB,
where, N is noise power in Watts, k is Boltzmann’s constant, which is the ideal gas law constant divided by Avogadro’s number, T is temperature in Kelvin units, and B is bandwidth in Hz. If you work that out at room temperature (298 K) and put it into dBm units, you get –174 dBm in a 1 Hz BW. Ken Javor Phone: (256) 650-5261 ________________________________ From: <[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Wed, 26 May 2010 11:00:53 -0700 To: <[email protected]> Subject: Re: [PSES] Radiated emission testing for automotive at low levels. Ken, I'm curious about the origin of the -174dBm. _______________________________________ _____________________________________________ Ralph McDiarmid | Schneider Electric | Renewable Energies Business | CANADA | Compliance Engineer From: Ken Javor <[email protected]> To: [email protected] List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: 05/26/2010 10:38 AM Subject: Re: [PSES] 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]> <mailto:[email protected]> <mailto:[email protected]> www.cetest.nl <www.cetest.nl> <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. - 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]>
