R&S ESU Instrument Functions
Analyzer Mode
4.200 Operating Manual 1302.6163.12 - 03
4.8.13.4 Measurement of Signal Amplitude Statistics
Digital modulated signals are similar to white noise within the transmit channel, but
are different in their amplitude distribution. In order to transmit the modulated signal
without distortion all amplitudes of the signal have to be transmitted linearly, e.g.
from the output power amplifier. Most critical are the peak amplitude values, of
course.
Degradation in transmit quality caused by a transmitter two port network is depen-
dent on the amplitude of the peak values as well as on their probability.
The probability of amplitude values can be measured with the APD function (Ampli-
tude Probability Distribution). During a selectable measurement time all occurring
amplitude values are assigned to an amplitude range. The number of amplitude val-
ues in the specific ranges is counted and the result is displayed as a histogram.
Each bar of the histogram represents the percentage of measured amplitudes within
the specific amplitude range.
Fig. 4.11 Simplified block diagram for APD measurement
Fig. 4.12 Display of the amplitude probability distribution
video
voltage
ADC
address
RAM
write
read
clock
logic
CPU
display
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