题目

英语翻译
1.信号不是周期出现,而只是持续一段时间,不再重复出现,如过渡过程,爆炸产生的冲击波,起落架着陆时的信号等,把这一类信号看成为非周期信号.分析非周期信号的思路是：在时域上,当周期T1→∞,周期信号变成为非周期信号；在频域上周期信号的频谱在T1→∞时的极限,变为非周期信号的频谱,即傅里叶变换.
2.信号在时域压缩α倍（α〉1）时,则在频域中频带加宽,幅值压缩1/α倍；反之信号在时域扩展时（α〈1）,在频域中将引起频带变窄,但幅值增高.

提问时间：2021-01-13

答案

1.Signal cycle is not there,but continued for some time,not repeated,if the transition process,blasts,the landing gear while landing signals,such signals can become non-periodic signals.Analysis of non-periodic signals ideas :in the time domain,when the cycle T1 → ∞,periodic signals into non-cycle signal; in the frequency domain signal cycle in the spectrum T1 → ∞ limit,and non-periodic signals into a spectrum,Fourier transform.2.In the time domain signal compression Europium times (Europium "1),in the frequency domain band widening,one-amplitude compression Europium times; Instead signal in the time domain expansion (Europium "1),in the frequency domain will lead to narrow frequency band,but the amplitude increased.