Filter
Top Products
I
-
Making Measurements Using Spectrum Analyzer Mode
Measuring Amplitude Modulation with the Fast Fourier Transform Function
Example 1: Use the manual FFT measurement to look at 60 Hz AM
modulation.
1. Connect a signal generator to the spectrum analyzer’s INPUT 75
Q.
Adjust the signal generator to produce an AM signal with a 60 Hz
modulation frequency.
2. Press (FREQUENCY] and set the spectrum analyzer center frequency to
the frequency of the modulated input signal. Press
@Gi),
10 MHz.
Press (FREQUENCY] again and center the signal on the spectrum analyzer
display.
3. Press
m),
1 MHz. Press [FREQUENCY] and center the signal on the
spectrum analyzer display again.
4. Press
Isw],
100
kHz.
(Re-center the signal, if necessary.)
Press
(SPAN)
200
kHz,
re-centering the signal again if it is necessary.
5.
Press VID BW AUTO HAM , 1
kHz.
The video bandwidth should be about
ten times greater than the highest modulation frequency of interest for
the best amplitude accuracy.
6. Press
BEF
LVL and turn the knob to change the reference level, placing
the signal peak within the top division of the screen. The signal peak
must be below the reference level. The signal amplitude moves up and
down because the spectrum analyzer catches the signal at different points
of modulated amplitude each time it sweeps.
7. Change the amplitude scale to linear by pressing [AMPLITUDE] and
SCALE LOG
LIN
so that LIN is underlined. The FFT will give incorrect
results when the spectrum analyzer is in Log mode.
Press
BBF
LVL and place the signal peak within the top division of the
screen.
8. Press
m),
0 Hz. The spectrum analyzer now operates as a fixed-tuned
receiver.
5-6