# Trouble with Spectrum Graph

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**starman**

25 Jan 2008

Posts:

I am having trouble with the Spectrum Graph feature. There are a couple of things that are causing me trouble.

Here is my scenario. I am acquiring a differential signal using channels A and B. These are displayed on the Scope Graph which I have stopped so that I have a static trace to work on.

I have set up a simple maths function (a-b) which displays the difference signal on the Maths Graph (A channel). (As a side note I do not seem to be able to hide the Maths B channel which I am not using, but I guess that should be the subject of a different post).

And thirdly I am displaying a Spectrum Graph (power density) sourced from the Maths function.

Now here are my issues:

Firstly is one of understanding. Is the Spectrum only calculated from what is displayed on the Maths Graph or from the Maths function across the Scope Graph, or across the complete acquired data set.? The reason I ask is that it doesn't seem to change when I pan the Maths Graph over different parts of the aqcuired signal which is what I am expecting (and hoping for). Nor does it change when I zoom in and out of the Scope Graph.

Secondly, I cannot get the Spectrum Graph to display reliably in this mode. I can have a valid Scope Graph trace, a valid Maths Graph trace and yet the power density spectrum is completely blank. Even if I press Fit which I expect to bring it automatically into the window still nothing is displayed.

Thirdly if I change any of the parameters on the Spectrum graph (e.g. Source, freq span, freq res) I would expect it to refresh immediately to reflect the change but again, nothing happens.

Any suggestions?

My software version is 4.622, firmware is 4.624

Here is my scenario. I am acquiring a differential signal using channels A and B. These are displayed on the Scope Graph which I have stopped so that I have a static trace to work on.

I have set up a simple maths function (a-b) which displays the difference signal on the Maths Graph (A channel). (As a side note I do not seem to be able to hide the Maths B channel which I am not using, but I guess that should be the subject of a different post).

And thirdly I am displaying a Spectrum Graph (power density) sourced from the Maths function.

Now here are my issues:

Firstly is one of understanding. Is the Spectrum only calculated from what is displayed on the Maths Graph or from the Maths function across the Scope Graph, or across the complete acquired data set.? The reason I ask is that it doesn't seem to change when I pan the Maths Graph over different parts of the aqcuired signal which is what I am expecting (and hoping for). Nor does it change when I zoom in and out of the Scope Graph.

Secondly, I cannot get the Spectrum Graph to display reliably in this mode. I can have a valid Scope Graph trace, a valid Maths Graph trace and yet the power density spectrum is completely blank. Even if I press Fit which I expect to bring it automatically into the window still nothing is displayed.

Thirdly if I change any of the parameters on the Spectrum graph (e.g. Source, freq span, freq res) I would expect it to refresh immediately to reflect the change but again, nothing happens.

Any suggestions?

My software version is 4.622, firmware is 4.624

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