Keeping ahead of the interference challenges: Page 3 of 5

September 06, 2016 // By Dean Miles, Tektronix
In our highly wireless world, interference is an unwelcome addition to the equation that results in noise, interrupts cell phone calls and just generally messes up communication. In the case of cellular networks, interference is actually part of the network. While more networks today have built-in features to detect interference, these tools often lack context as they are geared towards only a few types of signals and may only be able to measure the impact of the problem over a single channel.

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.

Figure 3: A real-time spectrum analyzer display shows much more information than a traditional display.

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.

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