The Importance Of Span Selection; Including All Important Signal Data - Agilent Technologies 89410A Operator's Manual

Analog Demodulation Concepts

The Importance of Span Selection

Including all important signal data

Analog demodulation is performed on the displayed span. Therefore, it is very
important to select your span carefully for the best results. If your display
truncates your signal's sidelobes, distortion will result as you can see in the sample
below.
The selected span truncates some sidebands of this phase modulated signal,
resulting in distorted demodulation.
The selected span includes all the sidebands, resulting in clean demodulation.
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