A common jammer is to shield mobile phone signals by emitting interference signals. By transmitting a high-power signal of a certain frequency, the surrounding electromagnetic environment is severely damaged, and the mobile phone cannot normally obtain and analyze the signal from the base station, thereby achieving the purpose of shielding the mobile phone signal.

Under normal circumstances, when a mobile phone enters a cell for the first time, the local cell base station will update and manage the location of the mobile phone, and at the same time allocate temporary user information such as a new temporary mobile user identifier to it. So as to determine the location of the community where you are. When the mobile phone jammer is working, it sends out an interference signal, which interferes with the effective signal on the broadcast channel frequency band of the base station. The interference signal increases the bit error rate of the mobile communication channel and reduces the signal-to-noise ratio of the channel, thereby affecting the mobile phone Effective reception of base station broadcast information, when the signal-to-noisratio is reduced to a certain extent. The mobile phone cannot normally decode the broadcast information of the base station, thus losing contact with the base station. The mobile phone cannot determine the service area where it is located many times, so the mobile phone in the interference area shows no signal and is not in the service area.

The second is the pseudo base station mode. When the jammer operates, the user's mobile phone signal can be forced to connect to the device, so that it cannot be connected to the public mobile communication network.

There are also some new jammers that use other principles to interfere with mobile phone signals, such as the pilot signal interference method, etc.