Technical data

Chapter 5 105
Spectrum Analyzer
Occupied Bandwidth (OBW) Measurement
Spectrum Analyzer
Occupied Bandwidth (OBW) Measurement
Occupied Bandwidth integrates the power of the displayed spectrum
and puts markers at the frequencies between which a selected
percentage of the power is contained. The measurement defaults to 99%
of the occupied bandwidth power. The power-bandwidth routine first
computes the combined power of all signal responses contained in the
trace. For 99% occupied power bandwidth, markers are placed at the
frequencies on either side of 99% of the power. This would leave 1% of
the power evenly distributed outside the markers. The frequency
difference between the two markers is the displayed occupied
bandwidth. The difference between the marker frequencies is the 99%
power bandwidth and is the value displayed.
The Occupied BW result corresponds to a span between the markers
and is a multiple of the span between two points. So, for a 10 MHz span,
the OBW will come in multiples of 25 kHz (10 MHz divided by 400
display points). Values will be 25 kHz, 50 kHz, 75 kHz, etc. For narrow
signals (TDMA, PDC, etc.) you will need to zoom in on the signal to get
a reasonably accurate Occupied BW result. For a 100 kHz span, the
OBW resolution will be 250 Hz (100 kHz divided by 400 display points).
The occupied bandwidth measurement can be made in single or
continuous sweep mode. The center frequency and reference level may
be set by you.
NOTE Zero-span is disabled in OBW measurement.