300 Chapter 5
Concepts
Analog Modulation Concepts
Modulation Distortion Measurement Concepts
Purpose
This measurement is used to measure the amount of modulation distortion
contained in the Modulated signal by determining the ratio of harmonic and noise
power to fundamental power. This measurement verifies the modulation quality of
the signal from the UUT.
Measurement Technique
Modulation Distortion is defined as:
Equation 5-3
where: P
total
= the power of the total signal,
P
signal
= the power of the wanted modulating signal, and
P
total
− P
signal
= total unwanted signal which includes harmonic distortion and
noise.
See Figure 5-11 on page 299. First, the received signal is demodulated and filtered
to remove DC, then the filtered signal is transformed by an FFT into frequency
domain. Next, total power in the total filter band is measured as P
total
, the peak
power of the modulated signal is computed as P
signal
, the square root of the ratio of
P
total
− P
signal
to P
total
is calculated. The result is signal’s modulation distortion. It
can be expressed as dB or %.
%
ModulationDistortion
P
total
P
signal
–
P
total
----------------------------------- 100%×=
To Next Page
Loading...
Need help?
General
