Making an OBW Measurement

The OBW Occupied bandwidth is closely related to channel power. It indicates how much frequency spectrum is covered by some given percentage (often 99%) of the total power of the modulated signal. marker provides an easy method for performing occupied bandwidth measurements. The occupied bandwidth, centroid, and offset are shown in the Markers Window and more detailed information is available in the OBW Summary Table.

Begin the OBW measurement by selecting a trace with spectrum information. In the following example, we have selected Trace A as the active trace window which contains the Spectrum trace.

The OBW marker only applies to trace data with spectrum data results; other trace data is not allowed. The OBW check box in the Markers > OBW tab is disabled for non-spectrum trace data results.
OBW measurement is allowed for Math functions as long as the X-axis data units are "Hz".

Make the Spectrum trace data the active display and then enable the OBW marker function to begin the occupied bandwidth measurement (Trace A in this example):

Select Markers > OBW and click the OBW check box.

As soon as the OBW marker is selected, the measurement starts and the VSA determines the occupied bandwidth using the default % Power setting (99%). This setting can be changed and any value from 0% to 100% specified.

OBW Data Results

The OBW marker measurement determines both the occupied bandwidth and the power in the band. In order to show all this data, the measurement results include the OBW marker readouts and an additional OBW Summary table:

OBW marker readouts: The OBW marker readouts are shown at the bottom of the OBW marker trace display.
OBW Summary table trace data: Complete set of OBW measurement results.

OBW marker readouts

When the OBW marker is selected for a Spectrum trace data result, the OBW marker readout in the Markers Window provides these results:

OBW: Occupied bandwidth (in Hz).
Centroid frequency: The midpoint frequency of the occupied bandwidth (in Hz).
Offset frequency: The difference between the VSA's measurement center frequency and the centroid frequency (in Hz).

This example shows the OBW marker and readouts for Channel 1 Spectrum trace data.

Notice that the trace display indicates that the OBW marker is active with the OBW message and highlights the bandwidth that contains the specified % Power with a colored background for easy viewing.

OBW Summary Table trace data

View additional OBW measurement results using the OBW Summary table. For more information, see OBW Summary Table.

To show the OBW Summary table, select the OBW Summary table that corresponds to the same trace that contains the OBW Marker.

The OBW Summary tawill only contain data when the OBW marker is enabled for the corresponding trace and that trace contains spectrum data.

In this example, the OBW Summary trace will be placed in Trace B to show detailed information for the OBW marker enabled in Trace A, which contains a Spectrum trace.

Make Trace B the active trace by clicking anywhere on Trace B.
Show the OBW Summary table in trace B:

Click Trace > Data > Marker > Trace B > OBW Summary

This screenshot above shows the OBW Summary table results for the OBW marker in Trace A. See OBW Summary Table for descriptions of the data results in the OBW Summary table.