Resolving Small Signals Hidden by Large Signals on Spectrum Analyzer

Chapter Resolving Small Signals Hidden by Large Signals

Measurement Guide and Programming Manual For Spectrum Analyzers PSA and ESA Series
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Measurement Guide and Programming Manual For Spectrum Analyzers PSA and ESA Series

  • 20Chapter 2 Measuring Multiple SignalsResolving Small Signals Hidden by Large SignalsMeasuring Multiple SignalsResolving Small Signals Hidden by Large SignalsThis procedure uses narrow resolution bandwidths to resolve two input signals with a frequency separation of 155 kHz and an amplitude difference of 60 dB. Step 1.Connect two sources to the analyzer input as shown in 17,Figure 17,2-6.Step 2.Set one source to 300 MHz at −10 dBm. Set the second source to 300.05 MHz, so that the signal is 50 kHz higher than the first signal. Set the amplitude of the signal to −70 dBm (60 dB below the first signal).Step 3.Set the analyzer as follows:Press Preset, Factory Preset (if present).Press FREQUENCY Channel, Center Freq, 300, MHz.Press BW/Avg, 30, kHz.Press SPAN X Scale, Span, 500, kHz.NOTEIf the signal peak is not present on the display, span out to 20 MHz, turn signal tracking on, span back to 2 MHz and turn signal tracking off:Press SPAN, Span, 20, MHz.Press Peak Search, FREQUENCY, Signal Track (On).Press SPAN, 2, MHz.Press FREQUENCY, Signal Track (Off).Step 4.Set the 300 MHz signal to the reference level: Press Peak Search, Mkr →, Mkr → Ref Lvl. NOTEThe ESA 30 kHz filter shape factor of 15:1 (PSA is 4.1:1) has a bandwidth of 450 kHz at the 60 dB point (PSA has a BW of 123 kHz). The half-bandwidth (225 kHz for ESA and 61.5 kHz for PSA) is NOT narrower than the frequency separation of 50 kHz, so the input signals can not be resolved.