Digital Signal Processing Reference
In-Depth Information
VCC
12 V
HP 35665A
Dynamic Signal
Analyzer
+
R1
100 k
1 mH
0.01
µ
F
Ω
V out
C1
0.1
F
µ
+
2N3904
C3
1
Carrier input
HP 3324A
Signal
Generator
R2
2.2 k
F
+
µ
Ω
Modulating signal
input
HP 3324A Signal
Generator
+
RE2
2.2 k
Ω
FIGURE 3.9
Practical Amplitude Modulation (AM) circuit.
a.
Compare the measured and simulated power spectrum (from Sec-
tion 3.3) of the fundamental and first four harmonics in mW, after
normalizing the peak values of the fundamental to 1 mW (0 dBm).
b.
Compute the percentage error between the computed and measured
power spectrum (mW). The percentage error is defined as:
Pc
,
comp
−
Pc
,
meas
n
n
%
error
=
Pc
,
comp
n
Exercise 5: Measurement of spectrum in Amplitude Modulation (AM)
signals.
The circuit diagram for the Amplitude Modulation setup is shown in Figure
3.9. Connect one HP 3324A synthesized generator to the carrier input of the
circuit. Set the carrier frequency at 50 kHz and amplitude at 10 volts. Simi-
larly, connect another HP 3324A synthesized generator to the modulating
signal input of the circuit. Set the modulating signal frequency at 2 KHz and
the amplitude at 0.1 volt. Then connect the output of the AM circuit to
channel 1 or channel 2 of the HP 35665A Dynamic Signal Analyzer, and
observe the AM signal in both the time and frequency domains. Set a center
frequency of 50 kHz and a span of 5 kHz on the Dynamic Signal Analyzer.
Measure the power spectrum in dBm of the carrier and the two sidebands.
Obtain the power spectrum of the AM signal. The power contained in the
Fourier coefficients is given as follows:
