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

  • 21Figure 14. Over-the-air measurement of a GSM 850 downlink transmission using the Agilent N934xC HSA with the trace “Maximum Hold” selectedFor radios that do not provide access between the transceiver and the antenna, the spectrum analyzer can be directly connected to the system antenna or connected to an external antenna with the analyzer placed in the area near the transceiver as shown in Figure 13B. During the discovery process, an omni-directional antenna is a good choice so that signals from all directions are measured from the surrounding environment. Omni-directional type antennas include the rubber-ducky and whip antennas.If possible, turning off the system transmitter allows the spectrum analyzer to measure in-band and co-channel interference with the lowest noise floor settings as previously discussed. In this case, it is assumed that any nearby out-of-band and adjacent channel transmitters have signal levels low enough so that the spectrum analyzer front-end is not overloaded.Capturing intermittent signalsIntermittent signals are often the most difficult to measure. The radio perfor-mance occasionally suffers from interference at what may seemingly be random times of the day. For cases when the interference is pulsed or intermittent, the spectrum analyzer can be configured to store the maximum trace values over many sweeps. Recalling the over-the-air measurement in Figure 3, the lower channel of the GSM 850 signal was only transmitting during a few time slots resulting in a measured waveform that displayed breaks in the envelope.Placing the spectrum analyzer in “maximum hold” mode, the instrument will fill in the gaps after several sweeps. The {Max Hold} selection is found under the [TRACE] menu on the Agilent HSAs and the results for the GSM 850 signal using the maximum hold is shown in Figure 14. It is now apparent from Figure 14 that the signals in the two channels have a similar spectrum and power distribution.Interference Measurement Procedure (continued)Max. hold870.4 MHz (channel 136)870.0 MHz (channel 134)