3-21 AM/FM Modulation Measurement (Option 509) Spectrum Analyzer Measurements
3-108 PN: 10580-00447 Rev. H Spectrum Analyzer MG
AM/FM Metrics
Field Master Series and Remote Spectrum Monitor instruments automatically detect the highest power audio
tone which is used as the fundamental tone for the audio signal in Signal-to-noise and distortion (SINAD)
measurement, therefore it is not required to define the frequency of the fundamental tone. SINAD is the ratio
of the total channel power relative to the unwanted signal power. Higher the value of SINAD, the better the
quality of the audio signal.
SINAD ratio measures AM/FM modulation distortion. It is calculated as the ratio of the channel power relative
to the power of the fundamental tone using a notch filter.
SINAD ratio (dB) is expressed in logarithmic term as follows:
Where, S = Signal Power, D = Distortion, N = Noise.
Distortion is defined as all signals in the demodulation bandwidth other than the wanted tone used to
modulate the transmitter under test, including spurious and sidebands created by non linearity in the
transmitter modulator. Refer to the graphical representation of SINAD measurement as shown in Figure 3-88.
Figure 3-88. SINAD Measurement
SINAD
SDN++
DN+
-------------------------
=
Amplitude(dB)
-100
0 kHz
1 kHz
2 kHz
3 kHz
4 kHz
5 kHz
-50
0
Demod Audio Frequency (kHz)
Noise
Notch Filter
Fundamental Tone Spurious
Harmonics
SINAD
To Next Page
Loading...
