How High‑School Exam Signal Jamming Works and the Countermeasures

During the Gaokao exam on June 7‑8, many students experience abnormal mobile signal quality because exam venues deploy high‑power jamming devices that severely affect nearby users' calls, data, and overall connectivity. All three major carriers have issued notices asking residents near test sites to be patient.

The jamming is not a perfect Faraday cage; instead, the devices emit strong electromagnetic noise across a wide frequency range, overwhelming the phone’s ability to communicate with its base station. This creates frequent call failures, dropped calls, and slow internet access.

Phones normally connect to the nearest base station by sending and receiving radio waves. When a jammer is activated, it generates noise signals that are much stronger than the legitimate base‑station signal, effectively drowning it out so the phone cannot hear the tower and becomes isolated.

Because the jammer’s noise covers only part of the spectrum, it mainly targets the limited 2G/3G/4G bands used by domestic carriers. However, the device sweeps across frequencies, making it difficult for ordinary phones to maintain a clear link.

Cheaters may try to bypass the jamming by using specialized radio equipment that operates on frequencies outside the jammer’s range, such as walkie‑talkie bands or hidden receivers embedded in earphones or glasses.

To detect such illicit transmissions, authorities deploy wireless monitoring stations and even a six‑rotor drone equipped with a radio‑frequency scanner. The drone can fly up to 500 m, map signal strength, and pinpoint the source of suspicious emissions, allowing officials to locate and confiscate cheating devices.

These monitoring systems can also capture the transmitted data, decode binary‑encoded answers, and reveal any encryption used, effectively exposing the cheating communication.

The article concludes with a reminder to respect exam integrity, encourages students to pursue telecommunications as a career, and wishes all candidates success.