Measuring frequency of interference
Traditionally, the various trace modes available in a spectrum analyzer are used to help characterize RF signals of interest. Peak hold, average and minimum hold are common. Even when employing these trace modes it is still difficult to determine how often a signal is occurring or if one signal is somehow related to other signals in the same span.
RTSAs provide a solution to this problem: a fast spectrum display with persistence effects. Remember that in a real-time spectrum analyzer, for any span up to the maximum real-time span, the instrument is not sweeping, which means it is capable of measuring the spectrum tens of thousands of times per second. But the spectrum cannot be displayed that fast. To solve that problem, spectrum analyzers with persistent displays were developed as shown in Figure 3.
A persistence display (or digital phosphor display) keeps track—pixel by pixel—of how often energy is being measured. The color of the pixel indicates how often a signal is present. With temperature scaling, red means a signal is on often while blue means it’s on less often. With the combination of fast spectrum measurements and persistence, infrequent events can be more easily identified.