Lambda SR1, Operation Manual, Page: 157 / 317

SR1 Operation 157
© 2014 Stanford Research Systems
2.4.5 THD Analyzer
The THD (Total Harmonic Distortion) analyzer uses FFT techniques to measure the total or relative
amplitude in two groups of user specified group of harmonics. Unlike the Time Domain Detector, which
uses time-domain techniques to integrate the total noise+harmonic power outside the fundamental the
THD analyzer uses the FFT internally to selectively measure only the amplitudes of harmonics.
The THD Analyzer Panel
Fundamental Frequency Selection
The THD Analyzer computes the power in two sets of harmonics, both relative to the same fundamental
frequency. The fundamental can either be a fixed frequency, or it can be "tuned" to any of the choices
listed in the tuning control. Selecting "Analog Gen A/B" or "Digital Gen A/B" tune the fundamental the
frequency of the selected channel of the specified generator. The Sweep 0/1 selections choose the
current sweep frequency of the inner or outer sweep.
Note that when possible, the "Generator" or the "Sweep" settings should be used over the "Measured
Freq." setting as they will often result in faster response and better measurement stability.