In-Channel Phase Modulating Interference - Agilent Technologies ESA-E Series User And Programming Manual

Making Modulation Analysis Measurements
Interpreting Measurement Results

In-Channel Phase Modulating Interference

Many signals are present in an integrated communications system.
Examples may include digital, baseband, IF, and RF signals. Crosstalk
between adjacent components and stages often leads to unwanted
signals in the output. The Modulation Analysis Personality can help
identify these signals, including in-channel phase modulating signals.
For a Wideband CDMA signal, PM interference appears as an aligning
of the symbol decision points in the center of each quadrant, forming
"lines" of dots. This line extends farther outward as the magnitude of
the PM increases.
1. Use the I/Q polar constellation diagram first to identify this problem.
Press
Wideband CDMA signal with in-channel phase modulation
interference. Note the variation of phase around the ideal symbol
reference points. Also observe how much larger the phase error
values are compared to those for magnitude error in the table.
The results shown were created with a phase modulation deviation
of 0.03 pi radians (about 5.5°) and a modulating frequency of 45 kHz.
Figure 4-26 Polar Constellation Showing PM Interference
46
I/Q Measured Polar Constln
. Figure 4-26 shows an example of a
Chapter 4