Power Spectrum Measurements

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Y-Axis Scaling

After the power spectrum is plotted, the Y-axis can be re-scaled to aid spectrum analysis. Activating Y-axis scaling causes the selected Y level to be plotted at the top of the screen and the rest of the plot to be re-scaled accordingly. The dB values will also be re-scaled using the top of the screen as the 0 dB reference with decreasing values displayed as the bottom of the screen is approached. With a power spectrum displayed, the Y-axis can be re-scaled relative to the position of the horizontal cross hair as follows:


1.      Adjust the horizontal cross hair to the desired reference level by:


  Dragging with the left mouse button in the left annotation margin of the bottom pane (or transform plot area).


   Using the ­↓ or ­↑ cursor control keys. Note that the bottom pane must be selected in order for the cursor control keys to move the horizontal cross hair. If not already selected, select the bottom pane for cursor control key operation by pressing F6. This is the keyboard accelerator keystroke for the View Toggle Pane command.


2.      Re-scale the spectrum plot relative to the horizontal cross hair by:


  In the Transform menu click on Scale DB.


   Choosing Transform Scale DB (ALT, T, S).


If the results obtained from this re-scaling operation are unsatisfactory, the default Y-axis scale can be restored by positioning the cross hair at the extreme bottom of the screen and repeating step 2 (in effect, re-scaling with the cross hair positioned at the extreme bottom of the screen).