Tektronix RSA7100 Series, Быстрый старт Руководство пользователя

Страница: 86 / 104

Operation
3. Select DPX Density from the Type drop-down list.
4. Set the DPX Density parameters as appropriate. You can do this one of the following ways:
Check the Show measurement box in the Density tab of the DPX Settings control panel to view the measurement
box in the display. Enter the Frequency and Amplitude in the Density tab.
Check the Show measurement box in the Density tab of the DPX Settings control panel to view the measurement
box in the display. Use the mouse to move and size the measurement box that appears on the display to set
the values for Frequency and Amplitude.
NOTE. If the Amplitude units (Setup > Analysis > Units) is set to Watts or Volts, you cannot move the measurement box
using a mouse. Set the amplitude units to any unit other than Watts or Volts to move or resize the measurement box.
To optimize DPX Density trigger settings for your particular signals, open the Trigger control panel. Use the controls for
changing the polarity of the trigger's threshold comparison (Higher versus Lower), the Threshold value, and the size and
location of the measurement box. Use the Frequency and Amplitude settings to locate the center of the box, and set the +/-
values to adjust the width and height of the measurement box.
For events that are partially masked by stronger signals, you will often need to adjust the density Threshold based on
density measurements of the event of interest and of the obscuring signal. For example, if the density of the background
color representing only the stronger signal is 7% and the density measurement including both signals is 9%, you would
set the Threshold to 8%.
If your expected signal is a continuous tone and you want to capture events when it hops to a different frequency or drops
to a lower amplitude, move the Density measurement box to surround the peak of the signal, select
Lower in the Density
control, and set Threshold to 100%. The instrument will trigger when the signal is absent from the measurement box.
Hint.
The density measurement is the average of the densities for each column of pixels in the box. If your measurement
box is wider than the peak of a CW signal, the density reading will be less than 100%. To get a 100% reading, you can
broaden the peak by increasing RBW or narrow the box until there are no colored pixels either above or below the box. The
signal should enter the left side of the box and exit the right side. It should not cross the bottom edge of the box.
66 RSA7100 Series Quick Start User Manual