另一种有用的曲线是幅度对频率的曲线,称为频谱。能够进行这种测量的仪器称为频谱分析仪。图2.74示出调幅中各种电压的频谱曲线。 当然,传播的能量仅是频率较高的分量:V_(LSB)、V_c、V_(USB)。标为V_(LSB)和V_(USB)的信号分别称为下边带信号和上边带信号。当未调制时,这两个边带的信号都不存在。因 Another useful curve is the amplitude versus frequency curve, called the spectrum. Instruments capable of making such measurements are known as spectrum analyzers. Figure 2.74 shows the spectral curves for various voltages in amplitude modulation. Of course, the energy transmitted is only the higher frequency components: V_ (LSB), V_c, V_ (USB). The signals labeled V_ (LSB) and V_ (USB) are referred to as the lower sideband signal and the upper sideband signal, respectively. When unmodulated, neither of these sideband signals exist. because