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RF Measurements Measurements
5-30 MS278XB OM
Occupied Bandwidth Measurement
The Occupied Bandwidth (OBW) measurement shows the bandwidth that includes most of the channel energy.
This is usually 99%, but can be adjusted. It also shows the bandwidth that is occupied down to X dB below the
signal level, which can also be adjusted.
When in the OBW measurement, the frequency, sweep and bandwidth parameters are used according to basic
instrument setup. The RBW must be sufficiently small to not affect the OBW reading. The attenuator and
reference level must be set correctly and the signal must be significantly above the analyzer’s noise floor to get
a reasonable measurement. The detector is automatically set to RMS detector.
During the measurement, the instrument integrates power over the entire span, then starts integrating out
from the center until the selected percentage is reached. The corresponding bandwidth is reported as OBW.
The Center of the measurement is the point where the integrated power is one half of the total span. The
instrument then starts at the center and move outward until the X dB value is crossed, then reports the X dB
bandwidth value.
The following measurement is made on a 2 GHz, 3.8 MHz QPSK modulated test signal. The analyzer is set up
with a 20 MHz span using all other default setups.
Figure 5-10. Occupied Bandwidth Measurement