Achieve Accurate RF Measurements by Understanding Spectral Purity (Download)
Spectral purity is a signal's characteristic stability. For testing purposes, a signal must remain stable in the short and long term. Selecting a signal generator with high spectral purity ensures that the measurements describe the device under test’s (DUT’s) performance rather than the signal generator’s limitations.
Drift or long-term stability is typically defined over a period of more than a second. Current signal-generator technology generally offers good long-term stability.
The primary concern is frequency changes in less than a second: short-term stability. These fluctuations are caused by non-deterministic signals like noise, 1/f flicker noise, and shot noise that modulates the carrier. Such perturbations impact both amplitude and phase.