Monitoring signal characteristics
R&S
®
SMM100A
425
User Manual 1179.1341.02 ─ 05
The display width is normalized for 2 symbols. It uses one-symbol "eye opening" in the
center of the display and 1/2-symbols to the left and right of the center eye for captur-
ing time transitions. Several hundreds curve segments are superimposed. The begin-
ning of the recording is synchronous to the symbol and chip clock pulse.
Application:
To analyze amplitude and time distortion elements (e.g. jitter) at high-
speed digital data systems. A high quality, unimpaired signal shows a clearly open eye
(horizontally and vertically).
Signal acquisition points:
See
.
CCDF display
The complementary cumulative distribution function (CCDF) displays the probability
with which the output signal exceeds the average power.
Figure 8-5: CCDF diagram of a 5 MHz LTE Signal (Level -30 dBm) and two reference curves
X-axis
= Level over the average signal power, where the average power (RMS) corresponds to the origin
Y-axis
= Probability of exceeding the average power, that is the percentage of time the signal spends at or
above the power level specified by the X-axis
Marker 1 = Interpolation: 10.3% of the samples exceed 3.3 dB above average; simularilly 1% of the samples
exceed 7.5 dB above avarage (not shown with a marker)
Marker 2 = The point where the trace crosses the x-axis; indicates the highest peak that is found in the sam-
ple block and is 9.6 dB higher than average.
The CCDF diagram is calculated over 8 KSamples and corresponds to a signal with
the following characteristics:
●
"Baseband > LTE" and "Test Model > E-TM1_1__5 MHz"
●
"Status bar > Level = - 30 dBm" and "Status bar > PEP = - 18.43 dBm"
The difference between the level and the PEP results in the peak to average ratio.
If the measurement is long enough, the displayed highest peak would correspond
to the calculated crest factor.
The PEP value does not indicate how often the peak level is reached. The CCDF
shows the probability for reaching a dedicated instantaneous power.
Displaying baseband signal characteristics in real-time
