Understanding Zero Span

Zero span mode on a spectrum analyzer is a powerful measurement technique that transforms the instrument to display power versus time. Instead of sweeping across a frequency span, the resolution bandwidth filter stays parked on a single frequency, enabling time-domain analysis similar to an oscilloscope but with higher dynamic range. In this tutorial, you’ll learn how to properly configure resolution bandwidth and video bandwidth for accurate zero span measurements. Explore practical applications including audio demodulation, channel power measurements, and analyzing pulsed or time-varying signals such as radar and TDD wireless communications. Proper RBW selection is critical to avoid pulse distortion.

What you’ll learn:

• How zero span mode works by fixing the resolution bandwidth at a single frequency to display power versus time, and the key differences between zero span measurements and oscilloscope measurements
• Best practices for configuring resolution bandwidth and video bandwidth in zero span mode, including why RBW must be at least as wide as the measured signal to avoid distortion and inaccurate results
• Practical applications of zero span including audio demodulation of AM/FM signals, channel power measurements using the RMS detector, and analyzing pulsed signals from radar or wireless communications using video or external triggers

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