Keeping ahead of the interference challenges: Page 4 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.

When operating with a real-time display, it’s important to take care when selecting the RBW filter. Just like in a regular spectrum display, the RBW filter selection will greatly affect the speed of the spectrum measurements. One of the key specifications for an RTSA is the probability of intercept (POI). This specification dictates the minimum signal duration that the instrument is guaranteed to detect. Selecting a narrow RBW will change the POI for the measurement—an important factor to be aware of.

 

Revealing the whole story

While a much greater amount of information can be obtained from the persistent display compared to a basic spectrum display, it doesn’t reveal the whole story. In modern radios there are many protocols that employ some form of clear channel assessment. Essentially, such radios are capable of determining how busy a channel is and will only transmit when no one else is using the frequency. Even a fast persistent display cannot show the timing relationships between two signals. To determine the timing of signals we need to use the spectrogram function as shown in Figure 4 which allows us to plot the spectrum data over time to determine how often signals are active.


Figure 4: The spectrogram allows you to record spectrum for long periods of time and playback problem periods.

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