About OBW Marker (Markers Properties)

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 easily performs generic occupied bandwidth (OBW) and X dB bandwidth (BW) measurements. The OBW measurement determines the band of frequencies that contain a specified percentage of the total power within the measurement span. The target % Power property specifies how much of the signal power is used to determine the OBW of the signal. The BW measurement calculates the X dB Bandwidth based on the signal's peak power. The peak power threshold is specified using the X dB Bandwidth Threshold setting.

Use the Region Shown setting to select whether to show OBW or BW on the selected spectrum trace and in the Markers Window (markers readout).

There is also an OBW Summary table which contains both OBW and BW results for the OBW marker on the corresponding trace.

OBW Measurement Algorithm

The OBW measurement dynamically computes the OBW for each measurement sweep. The OBW is defined as the frequency band in the measurement that contains a specific percentage of the total power in the measured frequency span. The measurement algorithm used for determining the occupied bandwidth uses the following process.

Compute the total power in the measurement span.
Determine the OBW lower frequency: Sum the power beginning from the measurement start frequency while increasing the frequency until the accumulated power is equal to [(100 - % Power)/2] of the total power. This is the OBW lower frequency.
Determine the OBW upper frequency: Sum the power beginning from the measurement stop frequency while decreasing the frequency until the accumulated power is equal to [(100 - % Power)/2] of the total power. This is the OBW upper frequency.
Determine the OBW. Compute the OBW as the upper frequency minus the lower frequency.
Determine the Centroid frequency: Compute the centroid frequency as the (OBW Upper frequency + OBW Lower frequency)/ 2.

BW Measurement Algorithm

Find the bin with the highest power. The signal bandwidth is computed based upon the peak in a frequency domain trace where the peak is the bin with the highest value (interpolation is not currently used to find the peak value so ensure there is enough resolution to the bins in the frequency domain trace for the accuracy desired).
Find the locations that first cross the user-supplied threshold value (X dB Bandwidth Threshold) relative to the peak value. Simple linear interpolation is used when finding the locations that first cross the threshold value when they are not exactly on bin.
Compute the BW after the first frequency whose bin level is below that threshold is found in both directions from the bin with the peak level. The difference in frequencies in each direction is computed. Bins close to DC are ignored in order to still be able to measure signal bandwidths in the presence of a large DC component.