[time-nuts] Question about KE5FX Tools -> PhaseNoise Tool

Sylvain RICHARD sr75pro at free.fr
Mon Oct 17 03:49:42 EDT 2011

   Le 16/10/2011 18:20, Peter Krengel a ecrit :

     As expected I got a horizontal line at -127dBm from 10-100Hz.
     Unexpectedly level changed from 100-200Hz as a falling curve down to
     -132dBm and went on horizontaly further at this level to 1kHz.
     During the measurement I observed the instrument and saw that it
     switched from
     RBW 10Hz to 100Hz so that I guess thats the reason for the
     descending level
     between 100 and 200Hz f-offset. So the observed effect seems to be a
     of the Anritsu instrument.
     Similar happened between 1-10kHz and so on.
     My question: How can I adjust that offset to get a smooth measuring

   This is known to happen. Here's a link [1] to an Agilent FAQ regarding
   the HP70000 series modular spectrum analyzers. It's an interesting case
   because you get different behavior (noise increases or decreases)
   depending of the combination of RF/IF sections you choose.
   Time to review the Friis formula [2].
   Have fun,
   [1] [1]Agilent FAQ : Why does the noise floor rise when changing RBW
   from 300 kHz to 100 kHz in a 71210C Spectrum Analyzer?
   If the link is broken, go to agilent.com, copy and paste "DANL
   comparison" with the quotes in the search box, select "Electronic Test
   and Measurement" and the site will offer the FAQ as "71210C: DANL
   comparison to 71200C".
   [2] [2]Wikipedia: Friis formulas for noise


   1. http://www.home.agilent.com/agilent/editorial.jspx?cc=US&lc=eng&ckey=1000003230:epsg:faq&nid=-11143.0.00&id=1000003230:epsg:faq&pselect=SR.GENERAL
   2. http://en.wikipedia.org/wiki/Friis_formulas_for_noise

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