Zero Span Mode versus SA44

Hello.

I just got a BB60C to replace my SA44.

Trying to look at FSK waveforms in zero span mode, but the behavior is not the same as the SA44B.

In frequency span mode I see the FSK signal at about -50 dBm and the noise floor about -95.

But when I go to zero span mode to see the signal, the zero span noise floor is -50 (even with my FSK signal off) and I can’t see anything.

What am I missing here. I don’t have the same problem on my SA44b. I guess this has something to do with instantaneous bandwidth, but I don’t know how to correct this.

Hi Paul,

Are you referring to the spectrum plot in zero-span mode? or the time plot?

In both plots, the input power setting will play a large factor in the noise floor. The BB60C has maximum sensitivity at -50dBm input power/reference level. You want to try to set your input power setting to ~5dB above your expected input level to achieve the best dynamic range.

In the spectrum plot, the noise floor is also affected by the RBW. You can lower the RBW in that plot, but you might have to increase the length of the captures to achieve lower RBWs.

In the time domain plot, the noise of the AM samples will be affected by the IF bandwidth setting. You can expect the time domain samples to decrease by 3dB every time you halve the IF bandwidth.

Let me know if you have additional questions.

Regards

[Author]

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