141
Demodulating AM Signals
Measuring the Modulation Rate of an AM Signal
5 Set the center
frequency, span, RBW
and 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-scale
type to linear.
• Press AMPTD Y Scale,
Scale Type (Lin).
The y-axis units will automatically set to
volts.
7 Position the signal peak
near the first graticule
below the reference
level.
• Press AMPTD Y Scale,
Ref Level, (rotate
front-panel knob).
8 Set the analyzer in zero
span to make
time-domain
measurements
a. Press SPAN X Scale, Zero
Span
b. Press Sweep/Control,
Sweep Time, 5, ms
9 Use the video trigger to
stabilize the trace.
• Press Trigger, Video. Since the modulation is a steady tone, you
can use video trigger to trigger the analyzer
sweep on the waveform and stabilize the
trace, much like an oscilloscope. See
Figure 10-1
If the trigger level is set too high or too low
when video trigger mode is activated, the
sweep stops. You need to adjust the trigger
level up or down with the front-panel knob
until the sweep begins again.
10Measure the AM rate
using delta markers.
• Press Peak Search,
Marker Delta, Next Right
or Next Left.
Use markers and delta markers to measure
the AM rate. Place the marker on a peak
and then use a delta marker to measure the
time difference between the peaks (this is
the AM rate of the signal)
Step Action Notes
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