General Description
R&S
®
CMW-KM645
16
User Manual 1173.9740.02 ─ 04
●
SINAD:
Signal to Noise and Distortion ratio; the inverse of the THD + N, converted
to a dB value; see description below.
●
SNR:
Signal to Noise Ratio, see description below.
The filter settings for the audio measurements are described in
Max/Ext results
The results in the Max/Ext column correspond to the largest measured frequency devi-
ation and the largest distortions, e.g. the maximum THD but the
smallest
SINAD and
SNR.
THD / SINAD / SNR measurements
Harmonics are signals at an integer multiple of the fundamental frequency. The funda-
mental wave is the first harmonic, the n"th" harmonic is n times the frequency of the
fundamental wave. The production of harmonic frequencies by an electronic system
when a signal is applied at the input is known as harmonic distortion. The following fig-
ure shows the fundamental wave (labeled M1) and the 2
nd
to 5
th
harmonics measured
with a spectrum analyzer.
Fig. 3-10: Harmonics spectrum
To perform a harmonics measurement, one or two fixed, sine wave audio test tones
are transmitted over the left and right audio channels. The frequency of the test tone(s)
is specified in the "Measurement Control > AF" section of the configuration dialog
("THD (N) Freq. Left" and "THD (N) Freq. Right").
The demodulated audio signal in each of the two audio channels is the sum of three
contributions:
●
Signal S:
S corresponds to the power P
1
of the demodulated audio signal at the
reference frequency "THD (N) Freq. Left" or "THD (N) Freq. Right".
●
Distortion D:
The distortion is calculated from the sum of the signal powers of the
2
nd
, 3
rd
, 4
th
... harmonics:
Measurement Results
深圳德标仪器
135-1095-0799
