CCDF provides better resolution than CDF for low probability signals,
especially when the y-axis is in log format. Presetting the analyzer
automatically selects log format ([
Data Format], [magnitude log(dB)]).
The analyzer plots CCDF using units of % for the y-axis and power (dB)
for the x-axis. Power on the x-axis is relative to the signal average power,
so 0 dB is the average power of the signal. In other words, a marker
reading that shows 12% at 2 dB means there is a 12% probability that the
signal power will be 2 dB or more above the average power.
The analyzer computes CCDF using all samples in the current time record.
Each successive measurement adds additional samples to the CCDF
measurement. Pressing [
Measurement Restart] or changing most parameters
under the MEASUREMENT keygroup restarts the CCDF measurement.
Tips CCDF measurements operate on time data. By default, time data is
uncalibrated. Therefore, make sure you enable time-domain corrections as
done in this procedure before making CCDF measurements.
For accurate CCDF measurements on burst signals, use triggering and
time-gating to include only the burst in the CCDF measurement. Including the
signal off-time degrades measurement accuracy. To learn how to use triggering
and time gating, see “To set up time gating” in chapter 4.
CCDF of Random Noise
When the y-axis is log format, the
CCDF display shows two curves: the
CCDF curve of your signal and the
CCDF curve for an ideal band-limited
Gaussian-noise signal.
In log format, the analyzer
automatically plots the ideal curve
(using the same color as the
graticule) so you can compare it with
that of your signal.
For comparison, this procedure set
the span to 5 MHz to band-limit our
random noise signal.
The CCDF measurement displays the number of
samples used to compute CCDF (Cnt:) and the
average power of your signal (Avg:).
Making Statistical Power Measurements
5 - 3
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