[问答题] 已知调幅波xm(t)=(100+30cosΩt+20cos3Ωt)cosωct,其中fc=10KHz,fΩ=500Hz。试求:(1)xm(t)所包含的各分量的频率和幅值。(2)绘出调制信号与调幅波的频谱。
[单选题]对于一阶环节,当输入信号X(t)=A时,输出信号Y(t)若以()的速度恒速上升,当达到稳态值Y(∞)=KA时所用的时间就是时间常数T。A .在t任意时刻B .在t=0时刻C .在t=∞时刻D .在t>0时刻
[单选题]已知某电路元件的电压u(t)=20sin(314t+30°)V,电流i(t)=5cos(314t+30°)A,这个元件是( )。A.电阻B.电感C.
[单选题]已知某电路元件的电压u(t)=20sin(314t+30°)V,电流i(t)=5cos(314t+30°)A,这个元件是( )。A.电阻B.电感C.
[单选题]已知某电路元件的电压u(t)=20sin(314t+30°)V,电流i(t)=5cos(314t+30°)A,这个元件是( )。A.电阻B.电感C.
[单选题]已知某电路元件的电压u(t)=20sin(314t+30°)V,电流i(t)=5cos(314t+30°)A,这个元件是()。A.电阻B.电感C.电容
[单选题]已知某电路元件的电压u(t)=20sin(314t+30°)V,电流i(t)=5cos(314t+30°)A,这个元件是( )。A.电阻B.电感C.
[单选题]已知某电路元件的电压u(t)=20sin(314t+30°)V,电流i(t)=5cos(314t+30°)A,这个元件是( )。A.电阻B.电感C.
[单选题]已知某电路元件的电压u(t)=20sin(314t+30°)V,电流i(t)=5cos(314t+30°)A,这个元件是()。A.电阻B.电感C.电容
[单选题]已知某电路元件的电压u(t)=20sin(314t+30°)V,电流i(t)=5cos(314t+30°)A,这个元件是( )。A.电阻B.电感C.