74Measuring NoiseMeasuring Noise Using the Noise MarkerMeasuring Noise Using the Noise MarkerThis procedure uses the marker function, Marker Noise, to measure noise in a 1 Hzbandwidth. In this example the noise marker measurement is made near the 50 MHzreference signal to illustrate the use of Marker Noise.Step Action Notes1 Set the analyzer to theSpectrum Analyzermode.• Press Mode, SpectrumAnalyzer.This enables the spectrum analyzermeasurements2 Preset the analyzer. • Press Mode Preset.3 Enable the internalreference signal.• Press Input/Output, RFCalibrator, 50, MHz.4 Set the center frequency,span, reference level andattenuation.a. Press FREQ Channel,Center Freq, 49.98, MHz.b. Press SPAN X Scale,Span, 100, kHz.c. Press AMPTD Y Scale,Ref Level, −10, dBm.d. Press AMPTD Y Scale,Attenuation, Mech AttenMan, 40, dB.5 Turn on the noise marker. • Press Marker Function,Marker Noise.Note that display detection automaticallychanges to “Avg”; average detectioncalculates the noise marker from anaverage value of the displayed noise.Notice that the noise marker floatsbetween the maximum and the minimumdisplayed noise points. The markerreadout is in dBm (1 Hz) or dBm per unitbandwidth.For noise power in a different bandwidth,add . For example, for noisepower in a 1 kHz band width, dBm(1 kHz), add or 30 dB to thenoise marker value.6 Reduce the variations ofthe sweep-to-sweepmarker value byincreasing the sweeptime.• Press Sweep/Control,Sweep Time, 3, s.Increasing the sweep time when theaverage detector is enabled allows thetrace to average over a longer timeinterval, thus reducing the variations inthe results (increases measurementrepeatability).10 log× BW( )10 log 1000( )×
