T 7.2.1.3 Amplitude Modulation

TPS 7.2.1.3
Solutions
because high signal frequencies lie in the
modulation spectrum at low frequencies.
Basically the following applies: The upper
sideband is in the normal position, the lower
sideband is in the inverted position.
The modulation index m amounts to approx. 60%.
Calculate the transmission bandwidths in DSB
based on the spectra. For f M = 2 kHz:
b = (22 – 18) kHz = 4 kHz = 2 · f M
.
For f M = 3 kHz:
b = (23 – 17) kHz = 6 kHz = 2 · f M
.
In general:
b = 2 f Mmax
(3-9)
5.2.3 The AM spectrum for modulation with a
square-wave signal
5.2.2 DSB SC
Signal parameter Analyzer settings
Table 5.2.2-1: DSB SC spectrum
Signal parameter Analyzer settings
A C : 2.0 V V 1 : 2
f C : 20.0 kHz b : 100 Hz
f r : 50 kHz
A M : 2.0 V T : 40 s
f M : 2 kHz
V 2
f
KHz
Measurement
S( n)
Name
V
S AM (n)
V
Theory
S AM (n)
2 18.00 LSL 4.5 1.1 1.00
2 ____ ____ ____ ____ _____
2 22.01 USL 4.5 1.1 1.00
V
V 2
Table 5.2.3-1: AM spectrum for
square-wave modulation
A C : 2 V V 1 : 2
f C : 20.0 kHz b : 100 Hz
f r : 50 kHz
A M : 2 V T : 40 s
f M : 2 kHz
f
KHz
Measurement
Name
S( n)
5 10 LSL 3 3.2 0.32
5 14 LSL 2 5,0 0.50
2 18 LSL 1 5.6 1.40
2 20 carrier 8.4 2.10
2 22 USL 1
5.5 1.38
5 26 USL 2
4.6 0.46
5 30 USL 3 2.7 0.27
5 34 USL 4 2.0 0.20
V
S AM (n)
V
Theory
S AM (n)
V
Diagram 5.2.2-1: DSB SC
spectrum
Diagram 5.2.3-1: AM spectrum for square-wave modulation
55