E1C07 09/14/2010
14:43:49 Page 267
δt = 0.1 ms
N = 256
y(t)
Truncated segment
10
0.10
0
–10
t (s)
2T 1
Nδt = 0.0256 s
10
8
6
4
2
0
Amplitude
y(t)
Truncated segment
10
0.10
0
–10
t (s)
10T 1
Nδt = 0.1024 s
10
8
6
4
2
0
200
180
160
140
120
100
80
60
40
20
0
Amplitude
Frequency (Hz)
y(t)
No truncated segment
10
0.10
0
–10
t (s)
8T 1
Nδt = 0.08 s
12
10
8
6
4
2
0
Amplitude
δt = 0.1 ms
N = 1024
δt = 0.3125 ms
N = 256
200
180
160
140
120
100
80
60
40
20
0
Frequency (Hz)
200
180
160
140
120
100
80
60
40
20
0
Frequency (Hz)
(a) N = 256, δ f = 39 Hz
(b) N = 1024, δ f = 9.8 Hz
(c) N = 256, δ f = 12.5 Hz
Figure 7.4 Amplitude spectra for y(t). (a) df ¼ 39 Hz. (b) df ¼ 9.8 Hz. (c) df ¼ 12.5 Hz.
7.2 Sampling Concepts 267