Specifications

Chapter 11 97
Demodulating AM and FM Signals
Demodulating an AM Signal Using the ESA Series
Demodulating AM and FM Signals
multiple times, keeping the signal of interest in the center of the
display until the span is 1 MHz:
Press
SPAN X Scale, Span, (↓), Mkr→CF.
Step 7. Set the analyzer into time-domain with zero span:
Press
SPAN X Scale, Zero Span.
Step 8. Change the resolution bandwidth to 100 kHz:
Press
BW/Avg, Res BW, 100, kHz.
Step 9. Set the top of the signal near the top of the display by changing the
reference level with the front-panel knob:
Press
AMPLITUDE Y Scale, rotate front-panel knob.
Step 10. Set the amplitude scale to linear and then re-adjust the reference level
to keep the signal centered in the display:
Press
AMPLITUDE Y Scale, Scale Type (Lin).
Press
AMPLITUDE Y Scale, Ref Level, rotate front-panel knob.
Step 11. Set the detector type to sample and turn on AM demodulation:
Press
Det/Demod, Detector, Sample.
Press
Det/Demod, Demod, AM.
Step 12. Listen to the demodulated AM signal (adjust the volume as necessary):
Press
Det/Demod, Demod, Speaker (On).
Step 13. Measure the modulation index (AM depth as a percentage):
Press
Sweep Time, 5, s.
Press
BW/Avg, Video BW, 30, Hz.
Press
AMPLITUDE Y Scale, Ref Level (use the front-panel knob to adjust
the trace to the middle of the screen).
Press
BW/Avg, Video BW, 100, kHz.
Press
Sweep, Sweep Time, 5, ms.
The middle horizontal graticule line represents 0% AM; the top and
bottom horizontal lines represent 100% AM.
NOTE The signal to the speaker is interrupted during retrace because the
analyzer is performing automatic alignment routines. To eliminate the
interruption and clicks between sweeps, turn the auto alignment
function off by pressing
System, Alignments, Auto Align, Off.
Refer to the specifications for information about operating the analyzer
with the alignments turned off.