Modulation Distortion Measurement Concepts; Purpose; Measurement Technique - Keysight N9030A Measurement Manual

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 DUT.

Measurement Technique

Modulation Distortion is defined as:
Equation 2-4
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
as P
is the signal's modulation distortion. It can be expressed as dB or %.
%
ModulationDistortion
where: P = the power of the total signal,
total
P = the power of the wanted modulating signal, and
signal
P - P = total unwanted signal which includes harmonic distortion and
total signal
noise.
, the square root of the ratio of P
signal

Modulation Distortion Measurement Concepts

P – P
total signal ×
= ---------------------------------- -
P
total
, the peak power of the modulated signal is computed
total
- P
total signal
35
100%
to P is calculated. The result
total
Concepts