Near the exam, you may have received some illegal small advertisements. Someone sold homemade communication tools at a high price and promised to send test answers during the exam. The so-called self-made communication tool is to give candidates a radio receiver, while criminals have a special radio transmitter in their hands. In a short time after the beginning of the test, they will answer the test contents outside the field, and then send the answers to the candidates in the test room to achieve the purpose of cheating.
In fact, these illegal communication tools only select the frequency band used outside the frequency band range of the mobile phone shield to avoid the monitoring of the mobile phone shield. But there are also countermeasures against these tools, because there are many kinds of anti cheating radio devices.
There is a radio monitor that can help monitor the electromagnetic wave signals in these very useful frequency bands. Before the examination, the signal intensity generated by various legal radio wave devices such as mobile phones, radio and television around the examination room will be recorded. After the test starts, the radio monitors in the car, suitcase and office can receive all signals in the whole radio wave band. Once the so-called "advanced and safe" illegal cheating tools begin to send answers to the examination room, there will be "an extra piece" of radio wave signals from unknown sources on the monitor, which is difficult to escape the "ear" of the precision detector.
Of course, criminals who sell answers can also reduce the signal strength of the transmitter to escape the monitoring of the radio monitor, but in this way, it is not easy for the receiver in the examination room to receive the signal. The answer seller can also make the cheating equipment "advanced", such as making the signal frequency used by the communication tools jump around constantly, which increases the detection difficulty of the radio monitor. However, in this way, the structure of the transmitter and receiver will be much more complex, the technical difficulty will become greater, and the price will be very high. In fact, the technical complexity of these cheating devices is generally far lower than that of professional radio monitors, many of which use systems that have been widely used in the market. The radio monitors can make it clear in a few seconds the signal transmission mode used by both sides of cheating, not only detect the signal, but also directly extract the information inside and hear what is said in the dialogue. Some monitors can also "suit the remedy to the case" according to the characteristics of the cheating signal. The noise signal of which frequency band is sent by the cheating radio signal for suppression and interference. In this way, cheaters may not easily hear the answer and read one or two sentences, and they will be immediately locked and disturbed by the monitor, leaving only noise in the headset.
In addition, no matter how precise the equipment used by the cheater is, the nature of "near, far and small" of electromagnetic wave must exist. Relying on multiple monitors placed in different positions, the position of the signal transmitter can be calculated according to the distance and the strength of the signal, and the answer emitter can be captured on the spot. That's why some people who hid in the corner of a residential building and sent answers to the examination room were arrested by the police before they were lucky to send them.