The volume of the filter is related to the rated working voltage, working current, cutoff frequency, insertion loss and manufacturing process of the filter. Filters with basically the same electrical performance have different volumes due to different manufacturing processes. When the electrical performance is close, the larger filter is cheaper (suitable for occasions with large installation space). The frequency point where the insertion loss of the filter is greater than 3dB is called the cutoff frequency of the filter. When the frequency exceeds the cutoff frequency, the filter enters the stopband. In the stopband, the interference signal will be greatly attenuated. Depending on the occasion where the filter is used (signal cable filtering or power line filtering), two methods can be used to determine the cutoff frequency of the filter. When filtering the signal cable, it is determined according to the bandwidth of the effective signal. The cut-off frequency should be greater than the bandwidth of the signal, so as to ensure that the useful signal is not attenuated. When filtering the power line or DC signal line, the effective signal frequency is very low, and the problem of signal distortion is not the main factor. Therefore, it is mainly determined according to the frequency of the interference signal, so that the interference frequency should all fall within the stopband of the filter.