Accurate Measurement of Signals Close to the Noise Floor on a Spectrum Analyzer

Because most spectrum analyzers are calibrated to read the true power of a sinusoidal signal, a correction factor is necessary to read the true power of a nonsinusoidal signal, such as noise. Consequently, when noise and a sine wave are both present, a correction factor that is a function of the signal-to- noise ratio is necessary to find the true signal power. For some spectrum analyzers the correction factor for pure noise is incorporated into the software, but the correction for signal plus noise is generally ignored. This report derives this correction factor, which is significant where the signal-to- noise ratio is near unity.