How the latest spectrum analysers help engineers to troubleshoot radio interference problems: Page 4 of 5

July 29, 2013 //By Anritsu Company
The exploding growth of wireless services has made interference – once uncommon – a fact of life for wireless and broadcast professionals. For example, a metropolitan area of approximately one million people may have 1,000 licensed two-way radios, 600 cell sites, and 100 broadcasters.
up, rotate the antenna to find the direction of the strongest signal. When the direction of the strongest signal is located, the user presses the trigger on the antenna handle to place a record of the direction on the map. Next, the user moves to a new location and repeats the direction-finding process. It helps the triangulation effort if the moves are made at a right angle to the direction last plotted.

Sometimes a map is not required for signal hunting. In the simplest cases, it can be faster to take direction finding readings with a signal strength meter, use the tried-and-true Max-Hold method, or simply travel until the signal strength readings increase. A signal strength meter is available on many spectrum analyzers.

Selecting the right spectrum analyzer

Some spectrum analyzers are more capable than others when looking for interference. Handheld spectrum analyzers clearly have an edge over bench instruments, since they can easily go to where the signal is located. If you are going to be spending hours away from power sources, long battery life is helpful.

The ability to see small signals in the presence of large signals that may be nearby in the RF spectrum is important, as well. A spectrum analyzer with a dynamic range of >106 dB in 1 Hz RBW allows users to see a small signal 90 or 100 dB below a strong signal, while both signals are present.

Another key capability is a fast sweep speed with a low resolution bandwidth, so the spectrum analyzer can sweep fast while resolving sufficient detail to see the interfering signal. For many interference hunts, a 1 MHz span is useful. A good spectrum analyzer can use a 1 kHz resolution bandwidth to create a noise floor at –126 dBm, with an update rate of 3 sweeps per second. Figure 3 shows a display of a handheld spectrum analyzer with a fast sweep speed and high resolution.

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