General Description
R&S
®
CMW-KM645
17
User Manual 1173.9740.02 ─ 04
D = P
2
+ P
3
+ P
4
+ ...
The R&S
CMW measures up to 10 harmonics at frequencies up to 21 kHz. (
Exam-
ple:
with a reference frequency of 3 kHz, the distortion measurement is based on
the 2
nd
to 7
th
harmonics.)
●
Noise N:
The noise N is the power of the noise floor.
The sum of all three contributions S + N + D is the total received audio power. S and D
can be obtained in frequency-selective measurements. To obtain the sum N + D, the
R&S
CMW uses a notch filter to eliminate the fundamental wave. To avoid suppression
of the higher harmonics, the bandwidth of the notch filter is automatically adjusted to
be smaller than the reference frequency. The final results are calculated as follows:
THD [%] = sqrt (D / S) = sqrt (V
2
2
+ V
3
2
+ V
4
2
...) / V
1
THD [dB] = 20 * log(THD [%]/100)
THD + N [%] = sqrt(N + D) / sqrt(S + N + D)
SINAD [dB] = 20 * log(100/(THD + N [%]))
SNR [dB] = 10 * log(S / N) = 10 * log(V
1
2
/ N)
The R&S
CMW displays THD [%] values up to 100 %. A results close to 100% may
indicate incorrect settings, e.g. a specified reference frequency which if off the actual
frequency of the transmitted test tone.
3.5.4 Selecting and Modifying Views
Use the "Display" parameters to select the views and to change the appearance and
contents of the views. The following "Display" hotkeys are available:
Hotkey
Description
"Select View ..."
Switch to a certain detailed view or overview.
Alternatively select a diagram in the overview and press ENTER or the
rotary knob.
Use "FM > Assign Views" to disable either the RF or AF measurements.
3.5.5 Common View Elements
Below the title bar, the view shows the most important signal routing, analyzer, and
input signal settings; see
chapter 4.2.1, "Signal Routing and Analyzer Settings"
Statistics in the result tables
Most detailed views show tables providing a statistical evaluation of results.
Measurement Results
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