以往AM发射机大多采用晶体振荡器产生激励信号,虽然频率稳定度能够达到要求,但是存在输出频率单一的缺点,频率合成是以一个或少量的高准确度和高稳定度的标准频率作为参考频率,由此导出多个或大量的输出频率,这些输出的准确度与稳定度与参考频率是一致的。这在广播发射机中有着广泛的应用。 In the past, most AM transmitters used crystal oscillators to generate excitation signals. Although the frequency stability can meet the requirements, there is a single disadvantage of the output frequency. The frequency synthesis is based on one or a few standard frequencies of high accuracy and high stability as reference frequencies , Thereby deriving multiple or a large number of output frequencies whose accuracy and stability are consistent with the reference frequency. This is widely used in broadcast transmitters.