Digital Signal Processing Reference
In-Depth Information
Si nus
Ti me domain
VC O
Sp ect rum
Fr eq . do mai n
Time domain
of source signal
72,5
70,0
67,5
65,0
62,5
60,0
57,5
55,0
72,5
70,0
67,5
65,0
62,5
60,0
57,5
55,0
72,5
70,0
67,5
65,0
62,5
60,0
57,5
55,0
72,5
70,0
67,5
65,0
62,5
60,0
57,5
55,0
72,5
70,0
67,5
65,0
62,5
60,0
57,5
55,0
f = 4 Hz
f = 8 Hz
f = 16 Hz
f = 32 Hz
f = 64 Hz
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
Frequency domain
of FM-signal
ms
2,50
2,25
2,00
1,75
1,50
1,25
1,00
0,75
0,50
0,25
0,00
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
4 Hz
Frequency swing 64 Hz
Frequency swing 64 Hz
8 H
z
Frequency swing 64 Hz
16 Hz
Frequency swing 64 Hz
32 Hz
Frequency swing 64 Hz
64 Hz
25
50
75
100
125
Hz
Illustration 172:
Influence of the frequency of the source signal on the bandwidth of the FM spectrum
Apart from the frequency swing
f
C
the frequency of the source signal f
S
also has an influence on the curve
and width of the FM spectrum. This is demonstrated here for various frequencies of the sinusoidal source
signal with a constant frequency swing
Δ
Δ
f
C
= 80 Hz.
All that remains now is to examine whether the choice of mid-frequency also influences the curve and
bandwidth of the FM spectrum (Illustration 173).
