Interference Testing with Handheld Spectrum Analyzers Manual

Interference Testing with Handheld Spectrum Analyzers Manual
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Interference Testing with Handheld Spectrum Analyzers Manual

  • 23The spectrogram can record 1,500 sets of spectrum data in a single trace file with an update interval that is set by the user. The HSA will automatically create another trace file to save continuously beyond 1,500 sets. For example, on the N9344C HSA sweeping across the full 20 GHz frequency span, the sweep time would be 0.95 seconds. In this case, in one single trace file, the user can set the spectrogram to store data over 48 minutes using an update interval of 1 second or up to 5 days using an update interval of 300 seconds. The spectrogram dis-play is activated using the {SPECTROGRAM} selection under the [MEAS] menu.Estimating the interferer’s locationOnce the interference is observed using the spectrum analyzer, understanding the type of signal, such as WIFI, cellular, or other may be helpful in estimating the interferer’s location. For example, a wireless equipment operator maintain-ing a cellular network may observe an “out of spec” transmission from an adja-cent frequency channel. Knowing that the type of interference is from another cellular system may provide clues that a nearby repeater may be improperly transmitting energy into the adjacent bands.The last step in the discovery process is locating the source of the interference. At this point, it is preferred that a directional antenna be connected to the spec-trum analyzer since these high gain antennas provide pointing capability within the wireless environment. Directional antenna types include yagi and patch antennas. Antenna gain of 5 dBi or higher is recommended for this application. For example, Agilent’s N9311X-508 directional antenna provides a 5 dBi gain over the frequency range of 700 MHz to 8 GHz.Observing the amplitude of the signal on the spectrum analyzer as the directional antenna is moved around the environment could potentially point to the physical location of the interference when the signal amplitude is at a maximum. Unfortunately multipath reflections in the surrounding environment could reduce the pointing accuracy so it is important to make the measurement from as high as possible such as on rooftops or tall buildings. Cellular base sta-tion (BTS) antennas are usually configured with sectorized antennas having a narrow beamwidth and, using a measurement configuration as shown in Figure 13A, may provide an approximate direction (sector) for the interference.By combining directional measurements from several locations around an environment, it may be possible to triangulate an approximate position for the interfering transmitter. The exact location of the source usually requires driv-ing or walking around a smaller area with the portable spectrum analyzer and directional antenna looking for the maximum signal amplitude. Once the source of the interference is located, the final step is to correct or remove the offending transmitter.Interference Measurement Procedure (continued)To make locating the interference source easier, connect a high gain directional antenna, such as a yagi or patch antenna, to the HSA.Hint: