Spectrum Analyzer Measurement Guide : Spectrum Analyzer Measurements : Occupied Bandwidth
 
Occupied Bandwidth
To select OBW measurement go to main menu and press MEASURE > MEASUREMENT >OBW. Occupied bandwidth measurements are set up using the SETUP Menu (Occupied BW). Occupied Bandwidth (OBW) is a common measurement performed on radio transmitters. This measurement calculates the bandwidth containing the total integrated power occupied in a given signal bandwidth. There are two different methods of calculation depending on the technique used to modulate the carrier.
• % Integrated Power Method: The occupied frequency bandwidth is calculated as the bandwidth containing the specified percentage of the transmitted power.
• > dBc Method: The occupied frequency bandwidth is defined as the bandwidth between the upper and lower frequency points at which the signal level is a desired number of dB below the peak carrier level.
Occupied Bandwidth Measurement
1. The status panel provides quick access to common spectrum analyzer settings. See STATUS PANEL (Occupied BW).
2. Dashed vertical lines and a shaded region define the main channel.
1. All occupied bandwidth measurement parameters are set via the SETUP menu. See SETUP Menu (Occupied BW).
2. Occupied bandwidth measurement results are shown in a table at the bottom of the display.
Frequency and span settings for many signal standards can be set as follows:
1. Select MEASURE on the main menu.
2. Select OBW from the MEASUREMENT button.
3. Select SETUP and then do the following:
• Set the % OBW power or set X DB (dBc) power value
• Select the METHOD (Percent (%) or dBc (X DB)
• Toggle OBW limit testing if you wish to see pass/fail test results
Occupied bandwidth is a constant measurement; after it is turned on, it remains on until a different measurement is selected or the sweep is paused. OBW is calculated at the end of each sweep.
STATUS PANEL (Occupied BW)
Below is the status panel with the corresponding minimized status panel icons for occupied bandwidth measurement.
Status Panel with Minimized Status Panel Icons (Occupied Bandwidth)
REF LEVEL
Sets the reference level of the top graticule line in the selected units. If the reference level offset is not zero, OFFSET REF LEVEL is displayed at this location.
SCALE/DIV
Sets the graticule scale/division for log-based units. This setting does not apply to linear units.
REF LEVEL OFFSET
Sets the reference level offset in dB units. This setting can compensate for the presence of external input attenuation or gain.
FREQ OFFSET
Accounts for frequency conversions outside of the analyzer. Refer to Setting Frequency Parameters.
ATTEN LEVEL
When auto attenuation is off, sets input attenuation.
PRE AMP
Toggles the low-noise front-end preamplifier on or off. Refer to Setting Amplitude Parameters.
TRACES/CURSORS
Displays the current status of up to six traces or cursors in a quick-view summary. When the measurement view is set to RF Spectrum, trace information is displayed in this area. When the measurement view is set to Spectrogram, cursor information is displayed in this area. Cursors are available in the Spectrum measurement with the Spectrogram view selected.
The summary information includes the trace or cursor number, type, mode, and detector type. The active trace will show a highlighted background with the mode and detector type restated under the table. In Spectrogram, a reference trace (T0) will show you the settings of the trace used to fill the spectrogram. The reference trace settings are applied to all traces and cursors while in Spectrogram view. Selecting a trace or cursor in the summary panel activates the pressed trace or cursor and opens the TRACE menu, allowing you to select and set up an individual trace or cursor as desired. Refer to Setting Trace Parameters.
SWEEP
Toggles the current sweep setting between continuously or sweep once. Refer to Setting Sweep Parameters.
FREQ REFERENCE
Indicates the current frequency reference source of Internal High Accuracy (used after GPS has lost sync, but while the internal clock still has good GPS reference), Internal Standard Accuracy, External, or GNSS (GPS) Hi Accy (requires GPS). The instrument automatically selects the frequency reference in the following order of priority: external, GPS, then the internal time base.
SETUP Menu (Occupied BW)
The occupied bandwidth SETUP menu is available in MEASURE > MEASUREMENT > OBW > SETUP. Once the OBW measurement is selected, the SETUP menu can be quickly accessed by tapping on the summary display area below the spectrum display.
SETUP Menu (Occupied BW)
 
% OBW POWER
Sets the percentage of the total power that is measured within the occupied bandwidth for the current measurement. The resulting occupied bandwidth and total power values are displayed in the measurements results table.
X dB
Sets the x dB value used for the "x dB bandwidth" measurement. The occupied bandwidth is the frequency range between two points on the signal that are x dB down from the highest signal point within the OBW span.
OBW LIMIT
Enables limit checking at the specified frequency. The limit test results show as a green PASS or a red FAIL in the measurement table.
METHOD
Select the measurement method to be PERCENT (%) or X (dB).
PRESET SETUP
Sets all OBW setup parameters to default. Turns off limits.