什么是工频电磁干扰？

市电频率（工频，我国工频为50HZ,中频为50Hz--10kHz,高于10kHz为高频）产生的电磁干扰信号。

由交流电源产生的干扰。“工频”在中国大陆是50Hz。

What is 工频 EMI Electro-Magnetic Interference?

the wavelength of 50Hz is too long such that there will be no significant interference. In general you need to have a conductor of the size with a length (can be diagonal length) comparable to one wavelength of the signal in order to induce EM energy to couple the noise into the electronic.

50Hz's wavelength -> WL * freq = speed of light
speed of light = 3*10^8
freq = 50
Now it is obvious that no practical electronics will have a size that big!

however if the noise is coupled CONDUCTIVELY (i.e. not radiated), then it can be a problem, especially to power signal. usually the noise will come from the wall power jack. But most electronics will have filter device to handle that. Or, you can put some ferrite bead device to wrap around the power cord to suppress the noise a bit. Make sure you check the frequency response for the bead that you are using though.