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Two questions:

(1) What is the impact of "reference level" on the time-domain signal viewed on the spectrum analyzer?

[My attempt] Mean power level of a time domain signal would move up and down on the display? However, the envelope of the time domain signal would be same. Correct?

(1) What is the impact of "RBW" on the time domain signal viewed on the spectrum analyzer?

[My attempt] Smoothens the fluctuations of the envelope of a time domain signal. Is that correct?

Thank you in advance.

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    \$\begingroup\$ Last time I checked a spectrum analyser displays a spectrum and not a time domain signal. \$\endgroup\$ – Andy aka Oct 26 '18 at 17:34
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    \$\begingroup\$ Spectrum analyzer with "zero span" (whichever supports. e.g., from keysight/agilent), you can see the time domain signal (but I would say it is an envelope of a time domain signal)... e.g. cf. ewh.ieee.org/r5/denver/sscs/Presentations/2012_10_Agilent1.pdf (slide 6) \$\endgroup\$ – learning Oct 26 '18 at 18:00
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(1) No. Reference level is the y-axis of the spectrum display of a time domain signal. Modifying it does not change the spectral shape, it just moves the display up/down.

(2) No. RBW does change the spectrum display, as it is the measurement bandwidth (kind of a frequency mask) that is applied to the spectrum display.

Addition: VBW smoothens the spectrum on the display.

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  • \$\begingroup\$ I agree that RBW improves the SNR (or change the spectrum), which is in a frequency domain. Also VBW smoothens the spectrum on the display, which is also seen in a frequency domain. \$\endgroup\$ – learning Oct 26 '18 at 18:57
  • \$\begingroup\$ But my questions are from time domain perspective, when you have zero span per se \$\endgroup\$ – learning Oct 26 '18 at 18:58
  • \$\begingroup\$ With zero-span, this Agilent device is just an oscilloscope. So RBW and RefLevel does not make much sense. These settings belong to frequency mode. \$\endgroup\$ – Stefan Wyss Oct 26 '18 at 19:09
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    \$\begingroup\$ When in zero-span the SA is in effect a receiver at some particular frequency. The RBW sets the IF filter bandwidth, so it acts as a low pass filter- the smaller the bandwidth the 'smoother' the time domain signal, however once your RBW is smaller than your (modulated) signal you will start to lose that information (whether that's important depends on what you are attempting to achieve with the measurement). For CW signals if the incoming signal starts to drift out of your IF bandpass, the time domain signal will start to drop. \$\endgroup\$ – isdi Oct 26 '18 at 20:14
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    \$\begingroup\$ With zero-span, this Agilent device is just an oscilloscope That's not what zero span does. In normal mode, the X-axis shows frequency, that frequency is is swept (in time) to make the plot. In zero span, the the sweep is stopped at the frequency you set. Then the X-axis shows time and Y-axis power in the frequency band you set. An oscilloscope shows an unfiltered signal. A SA in zero span still filters. \$\endgroup\$ – Bimpelrekkie Oct 26 '18 at 21:00

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