Signal analyzer having independent analysis and display scales

Measurement instruments, such as spectrum analyzers and network analyzers, employ video bandwidth filtering, averaging and other types of signal conditioning to improve measurements of applied signals. For example, video bandwidth filtering within a spectrum analyzer decreases measurement variance when signals are measured in the presence of noise. Video bandwidth filtering of a signal is most advantageous when the signal is represented using an analysis scale that is most appropriate to the nature of the applied signal. When the applied signal is a continuous-wave signal, the effect of noise is minimized when video bandwidth filtering is performed with the signal represented on a first analysis scale-the logarithmic scale. When the applied signal is a pulsed radio frequency (RF) signal, the measurement of the pulse envelope shape of the signal is most accurately obtained when video bandwidth filtering is performed with the signal represented on a second analysis scale-the linear, or voltage, scale. When the applied signal is from a communication network having spectrally separated channels, adjacent channel power measurements are most accurately obtained when video bandwidth filtering is performed with the signal represented on a third analysis scale-the power scale. The effect of noise on spectrum analyzer measurements is discussed in Hewlett-Packard Company's Application Note 1303, Spectrum Analyzer Measurements and Noise. A signal analyzer has an analysis scale and a display scale that are independently selectable. The signal analyzer receives a first representation of an applied signal and provides from the first representation at least two alternative representations. A first selective input enables a designated one of the alternative representations to be applied to a filter to reduce variance of the designated representation. The signal analyzer then converts the received one of the alternative representations having reduced variance to at least two alternative display scales. A second selective input enables a designated one of the alternative display scales to be displayed on a monitor, display screen or other output device of the measurement instrument or system. Independent control of the first selective input and the second selective input via a user interface enables the analysis scale-the scale, or representation, to which the filter is applied, to be selected independently of the scale on which the representation having reduced variance is