通过调节载波频率可使外差法产生的差频在零频率点附近变动，从而使得双稳系统的输出信号发生特征极为明显的变化，为频率检测提供可靠的检测依据。(By adjusting the carrier frequency, the difference frequency produced by the heterodyne can be changed near the zero frequency point, which makes the output signal of the bistable system extremely obvious, and provides a reliable test basis for the frequency detection)