The working principle of mobile communication is to connect wireless devices (mobile phones, etc.) and base stations through radio waves of a certain frequency, and complete the transmission of data and sound with a certain baud rate and modulation method. The mobile phone communication is to connect with the base station through the uplink frequency, and then transmit the signal to the mobile service exchange to complete the call. In the standby state, the mobile phone is connected to the base station through the broadcast control channel. Once there is a need for a call, it first asks the base station for instructions, and assigns it to the mobile phone service channel according to the specific conditions of the near-terminal channel, so that the mobile phone jumps to the service channel for calls and data transmission. At the same time, in order to receive and complete communications effectively, a sufficient signal-to-noise ratio must be guaranteed.
Based on the above working principle, a wifi jammer is generally composed of a power supply, an electronic scanning control unit, a segmented radio frequency module, an amplifying unit, and a transmitting antenna unit. The wireless signal jammer generates a scanning signal, after the inverter, modulates the oscillator to the mobile communication working frequency band, and then amplifies the power by a power amplifier and a voltage regulator tube to control the power, and transmits the amplified frequency scanning signal to the air through radio waves. When the mobile phone receives the information signal, due to the garbled interference caused by the frequency sweep signal (increase the ratio of the noise signal to the device threshold), the mobile phone cannot receive the normal data sent by the base station, so it cannot connect with the base station normally, resulting in the mobile phone and the base station. Communication network separation. The mobile phone shows that the search network has no signal, no service system, etc., so as to achieve the blocking effect.
During operation, the WiFi jammer moves back toward the high end of the channel from the low frequency at a certain speed. When the mobile phone receives the information signal, the scanning speed will cause garbled interference, and the mobile phone cannot detect the normal data from the base station, so that the mobile phone cannot establish a connection with the base station, so as to achieve the purpose of shielding the mobile phone signal, and the mobile phone displays network search, no signal, no service. system, etc.
The interference power of the signal screen is fixed, and the impedance radius of the impedance space is determined by the channel attenuation and the signal level of the base station at the receiving end. In order to realize the interference of the WiFi signal jammer to the mobile network, it must be ensured that the field strength of the signal sent by the WiFi jammer is greater than that of the signal in the interference area. The closer the interference point is to the base station, the stronger the field strength and the smaller the effective interference area. Conversely, the farther the interference point is from the base station, the smaller the effective interference area and the larger the effective interference area.
It can be seen that under a certain transmission power, the interference range depends on the field strength of the interference area. No matter how much the power of the WiFi jammer is, as long as the transmission power is fixed, the farther the distance is, the weaker the interference signal will be, and the interference will be lost. ability. Below is a comparison table of distance and path attenuation. Once again, the theoretical shielding area radius with reference value can be determined from the output channel power of the WiFi signal jammer, the signal level of the base station, and the gain of the shielded wire.