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Spectrogram

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dedalmati
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Joined: March 5th, 2017, 8:07 pm
Country: Argentina

Spectrogram

Post by dedalmati » May 17th, 2020, 4:43 pm

I do not understand how the time/div setting in the spectrogram behaves.
Using markers I am able to measure time between events (and the measurements are OK) It shows 100,473 mS but it has no relationship with the time/div setting which is...1.90 ms. (unless there are 50 divisions in few pixels...)

w2aew
Tektronix Applications
Tektronix Applications
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Re: Spectrogram

Post by w2aew » May 17th, 2020, 6:57 pm

The Spectrogram display has a bit of a dual personality:

- When the acquisition length of the RSA is only long enough to process 1 full spectrum per acquisition, then the Spectrogram simply shows a collection of acquired spectrum results - one per acquisition. In this condition, the timestamps of each entry of the spectrogram are maintained, but the time/division control is essentially meaningless (since the time between acquisitions can vary based on a number of conditions). This is how the Spectrogram works when the user hasn't specifically increased the acquisition length beyond the automatic setting based on the Resolution Bandwidth setting.

- When the RSA is setup to acquire a long seamless acquisition of IQ data, then the Spectrogram is built from multiple spectrum computations taken sequentially through the seamless IQ data. By default, the time interval between the spectrum lines in the spectrogram is equal to the Spectrum Length (which is a function of the RBW setting). The time/div setting will be 50x the spectrum length because there are 50 spectrum lines between each tic on the left edge of the Spectrogram. You can choose to increase the time/div (which will combine >1 spectrum per line), or decrease the time/div, which will result in overlapped Spectrum processing (reducing the interval between the spectrogram lines).

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