User`s guide

Agilent PXT Wireless Communications Test Set
User’s Guide
198
Last Span toggles between the two most recent span settings.
The RBW defaults to an auto setting of 10 kHz, but can also be set manually.
Access the OBW Power setting by selecting the Meas Setup front-panel key. This setting specifies the
percentage value of power contained within the OBW measurement result. For example, if OBW Power is
set to 99%, the OBW result means that 99% of the power is contained within that bandwidth. The power
in twice the nominal system bandwidth is regarded as 100 %.
Complementary Cumulative Distribution Function (CCDF) Measurement
Key Path:
Mode > SA > Spectrum > MEAS > CCDF
Figure 6-4: CCDF measurement
The complementary cumulative distribution function (CCDF) is a statistical-power calculation. The
measurement computes the average power of all measured samples. This becomes the 0 dB point at the
left end of the horizontal axis. The average value and the percentage of samples greater than the average
value are displayed in the top right-hand corner of the display.
All power samples are normalized to the average power value and expressed in dB terms. The graph is
computed by considering power samples which are greater than the average power. Each of these
samples is placed in a bin between 0 dB and 20 dB. As the count progresses the graph is calculated for
each bin. The ordinate of the CCDF graph for a bin is calculated as the number of points in bins to the right
of the current bin (for example, of a higher power) divided by the total number of power samples to date –
including those less than the average power value. As a reference, CCDF graph for a Gaussian distribution
is displayed.
A table shows the power values in dB terms for some CCDF values. The peak power in dB and dBm terms
is also reported in the table.