I agree. A modern machine adjusts the raw data or noise floor for any and all transducer/amplifier/attenuator factors, and if the transducer factor is not flat, neither will be the adjusted noise floor.
The only reason we do things this way is an ³embarrassment of riches² in processing power. Absent a digital controller, the sane way to take data would be to adjust the limit for the transducer factors and arrive at an adjusted limit in terms of dBuV, or dBm. Consider the number of computations involved in adjusting a thousand data points across a screen for the transducer factors, vs. a simple flat or log-linear limit and transducer factors that only need be reentered at the next frequency at which they have changed by some set amount from the last frequency, such as 1 dB, or 0.5 dB. The adjusted limit represents orders of magnitude less computation, plus one can reverse engineer an adjusted limit if one knows the transducers in use, whereas adding factors to a signal above noise renders this impossible. Ken Javor Phone: (256) 650-5261 From: "McDiarmid, Ralph" <[email protected]> Reply-To: "[email protected]" <[email protected]> Date: Tue, 23 Feb 2016 16:42:47 -0800 To: <[email protected]> Subject: Re: [PSES] Spectrum analyzer and noise floor I would like to explain to a colleague why the noise floor on a SA does not look flat as it sweeps across a given frequency range after antenna factors, cable factors, external gain and external attenuation are programmed into its display function. I think it breaks down to these fundamental points: 1. the SA receiver has noise in its attenuator, mixer and filter circuits (say -80 dBm, and maybe flat within a limited frequency range) 2. the external amplifier has some noise too, but its gain lowers the noise floor created by #1 (also flat within a limited frequency range) 3. the cables have losses which are frequency dependant, and those can be entered as loss factors into the SA (shapes the noise floor a little and those losses raise the noise floor) 4. the antenna has a gain which is frequency dependant with several dB of hills and valleys across its usable frequency range (that really shapes the noise floor more than 1, 2 or 3 above) 5. noise floor shape caused by #4 is the mirror image of the antenna factor vs frequency Is that a decent summary? . Ralph McDiarmid Compliance Engineering Residential/Commercial Solar Business Schneider Electric D +1 (604) 422 2622 x62622 E [email protected] <mailto:[email protected]> 3700 Gilmore Way Burnaby BC Canada - ---------------------------------------------------------------- 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.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.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.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) 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]>
