141Demodulating AM SignalsMeasuring the Modulation Rate of an AM Signal5 Set the centerfrequency, span, RBWand the sweep time.a. Press FREQ Channel,Center Freq, 300, MHz.b. Press SPAN X Scale,Span, 500, kHz.c. Press BW, Res BW, 30,kHz.d. Press Sweep/Control,Sweep Time, 20, ms.6 Change the y-scaletype to linear.• Press AMPTD Y Scale,Scale Type (Lin).The y-axis units will automatically set tovolts.7 Position the signal peaknear the first graticulebelow the referencelevel.• Press AMPTD Y Scale,Ref Level, (rotatefront-panel knob).8 Set the analyzer in zerospan to maketime-domainmeasurementsa. Press SPAN X Scale, ZeroSpanb. Press Sweep/Control,Sweep Time, 5, ms9 Use the video trigger tostabilize the trace.• Press Trigger, Video. Since the modulation is a steady tone, youcan use video trigger to trigger the analyzersweep on the waveform and stabilize thetrace, much like an oscilloscope. SeeFigure 10-1If the trigger level is set too high or too lowwhen video trigger mode is activated, thesweep stops. You need to adjust the triggerlevel up or down with the front-panel knobuntil the sweep begins again.10 Measure the AM rateusing delta markers.• Press Peak Search,Marker Delta, Next Rightor Next Left.Use markers and delta markers to measurethe AM rate. Place the marker on a peakand then use a delta marker to measure thetime difference between the peaks (this isthe AM rate of the signal)Step Action Notes
