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 s