Why Make Measurements At Baseband - Keysight X Series Measurement Manual

Concepts
Baseband I/Q Inputs (Option BBA) Measurement Concepts
In receivers, baseband I/Q analysis may be used to test the I and Q products of I/Q
demodulators, after an RF signal has been downconverted and demodulated.

Why make measurements at baseband?

Baseband I/Q measurements are a valuable means of making qualitative analyses of
the following operating characteristics:
• I/Q signal layer access for performing format-specific demodulation
• Modulation accuracy – that is,. I/Q plane metrics:
• Code-domain analysis (including code-specific metrics)
• CCDF of
• Single sideband (SSB) metrics for assessing output quality
• Basic analysis of I and Q signals in isolation including: DC content, rms and peak
Comparisons of measurements made at baseband and RF frequencies produced by
the same device are especially revealing. Once signal integrity is verified at
baseband, impairments can be traced to specific stages of upconversion,
amplification, or filtering by RF analysis. In addition, impairments to signal quality
that are apparent at RF frequencies may be traceable to baseband using baseband
analysis.
measurements (for example, CDMA, GSM, W-CDMA).
— rho
— error vector magnitude; rms, peak, or 95%
— carrier feed-through
— frequency error
— magnitude and phase errors
2 2
I + Q
to peak levels, CCDF of each channel
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