I have a basic Rigol spectrum analyzer that sweeps across a range of frequencies and displays the amplitude of the signal.

When we go to a testing lab, their expensive spectrum analyzer has a mode where you put in a fixed frequency and it measures the duty cycles of your signal in the time domain.

What is that time-domain / duty cycle reading called for spectrum analyzers?


Since the input frequency is fixed you can set the spectrum analyzer to this frequency and then change the X-axis to display amplitude over time instead of over frequency.

This mode is called zero span mode. Here's an example:

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The X-axis shows time from 0 (trigger point) to 10 ms

The Y-axis shows the signal amplitude

Note the "Span 0 Hz" in the bottom right corner Here the signal(s) are present at 3 MHz in a 3 MHz (-3 dB) resolution bandwidth.

So signals between 1.5 MHz and 4.5 MHz show with nearly the correct (less than 3 dB attenuation) amplitude.

  • \$\begingroup\$ Your the man. This is totally your wheelhouse. Not certain if my Rigol can change the X-axis, but that's enough to go on. \$\endgroup\$ – Leroy105 Jul 11 '18 at 16:06
  • \$\begingroup\$ I obviously have been playing with spectrum analyzers too much in my life ;-) I would be surprised if the "zero span" is not available since it just switches off the sweeping of the internal signal generator. If you cannot find it just try setting Frequency Span = 0 Hz and see what happens. \$\endgroup\$ – Bimpelrekkie Jul 11 '18 at 16:07
  • \$\begingroup\$ Evidently 83 other people in the universe have wondered how to do zero span mode on a Rigol. youtube.com/watch?v=qmXb_hmUZHk (HA). \$\endgroup\$ – Leroy105 Jul 11 '18 at 16:10
  • \$\begingroup\$ Youtube takes all the challenges out of life ;-) \$\endgroup\$ – Bimpelrekkie Jul 11 '18 at 16:11
  • \$\begingroup\$ Yet web answers include standing on the shoulders of giants and mice 🐁 so always check your sources for expertise. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 11 '18 at 16:24

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