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

  • 16Knowing that the vertical scaling is set to 10 dB per box it is easy to see that the amplitude of the interference is approximately 30 dB larger than the main signal. As the interfering signal is the larger of two signals entering the input to the analyzer, it would be the power of interference that may overdrive the front-end of the spectrum analyzer.Figure 9 shows the spectrum of only the main signal using a narrower span of 20 MHz and a center frequency of 2.42 GHz. Even though the interference is not displayed with a 20 MHz span, the interference is still being applied to the input of the analyzer and could overload the front-end of the analyzer. In some applications it may be necessary to place a filter on the input to the spectrum analyzer in order to remove any large amplitude signals that are not part of the measurement but may overload the analyzer’s down-converter. It is always the largest signal at the input to the analyzer that sets the top end of the “dynamic range” for the instrument even if the signal is not shown on the instrument display.Figure 8. Measurement of two wideband signals with an adjacent channel interference having 30 dB more power than the desired signal. Note that both signals are easily observed using a frequency span of 60 MHzExample: Properly setting power levelsTo provide an example of the proper setting for the power levels entering a spectrum analyzer, Figure 8 shows the measured spectrum of two wideband signals. The main signal centered at 2.42 GHz and the adjacent channel interfer-ence is centered at 2.444 GHz. In order for both waveforms to be observed on the same display, the Agilent HSA center frequency was set to the midpoint of 2.432 GHz using the [FREQ] button and the frequency span was set to 60 MHz using the [SPAN].Receivers and Spectrum Analyzers (continued)Main signal30 dB2.444 GHz2.42 GHzInterferenceSpan 60 MHz