2．利用FFT对信号进行谱分析



对于连续信号xa(t)=cos(2πf1t) +5cos(2πf2t) +cos(2πf3t) ，其中f1=6.5kHz, f2=7kHz, f3=9kHz, 以采样频率fs=32 kHz对其进行采样，

（1）对xa(t) 信号采集16点样本，分别作16点和补零到256点的FFT，并分别绘出对应的幅频特性曲线。

（2）对xa(t)信号采集256点样本，分别作256点和512点的FFT，并分别绘出对应的幅频特性曲线。

（3）比较（1）和（2）中的结果，分析采样点数和傅里叶变换点数对FFT的影响，说明高密度频谱和高分辨率频谱的特点与区别。

-2. The signal using the FFT spectrum analysis



       　For continuous signal xa (t) = cos (2πf1t)+ 5cos (2πf2t)+ cos (2πf3t), where f1 = 6.5kHz, f2 = 7kHz, f3 = 9kHz, sampling frequency fs = 32 kHz is sampled,

(1) xa (t) signal acquisition 16:00 samples, respectively, for 16:00 and zeros to the 256-point FFT, and were drawn corresponding amplitude-frequency characteristic curve.

(2) xa (t) signal samples collected 256 points, respectively, for 256 points and FFT 512 points, and were drawn corresponding amplitude-frequency characteristic curve.

(3) Comparison of (1) and (2) the results, analyze the impact of sampling points and the Fourier transform of FFT points, indicating that the spectral characteristics and differences between high density and high resolution spectrum.