This is because the teachers thought that students would cheat in the college entrance examination, and they would also use various high-end electronic communication equipment, so they brought in the signal shielding device.
Although a mobile phone is a wireless communication device used wherever it goes, there is also an invisible line dragging it, which is the mobile phone base station. Whether a mobile phone makes or receives a call, the first step is to establish a connection with a nearby mobile phone base station. If you hold a mobile phone in your left hand and your right hand, and use the left-hand mobile phone to dial the right-hand mobile phone, the electromagnetic waves of the mobile phone are not transmitted directly from the left hand to the right hand, but will be transmitted from the left-hand mobile phone to hundreds of meters away The mobile phone base station, and then make a big circle and transmit it back to the right mobile phone (except for the Bluetooth function). Normally, the base station elder brother and the mobile phone younger brother are chatting hotly. The radio wave signals sent by both sides come and go, but when the jammer is turned on, it will "beat gongs and drums" around the mobile phone, and the power of the received base station signal is higher than that of the mobile phone. Many times the "noise" radio wave signal, the mobile phone can't hear what the base station is talking about, and cannot receive the signal of the base station normally, the connection between the two is cut off, and the mobile phone will become an island, no matter if you make calls, send text messages or other various functions , are paralyzed.
Therefore, operators should issue warm reminders. Because so much noise comes out, not only the signal of the examination room is "shielded", but the wireless signal around the examination room will also be interfered, which seriously affects the call quality of mobile phone users around the examination room. If the call quality is poor, you complain, and the operator is of course anxious. However, this can't really blame the operators! So, once again, a warm reminder, for the sake of the flowers of the motherland, please be patient for three days.
Does this shield really work?
The entire frequency band of electromagnetic waves ranges from a minimum of a few Hz to a maximum of tens of hundreds of GHz. The range is very large. Each section may be used as a communication signal. However, except for a small number of very professional equipment, ordinary shielding devices are "The voice is not loud enough", "the tone is not complete", a shield can only shield a small part of the frequency band, and the communication tool can use the unshielded frequency band to communicate. Of course, all the 2G, 3G, and 4G mobile phone services of several domestic communication companies are concentrated in several small frequency bands, and the jammers in the examination room can still concentrate on these frequency bands. When the mobile phone jammer is working, it will "sweep" electromagnetic waves from low frequency to high frequency in various frequency bands, interfering with the connection between the mobile phone and the base station.
So, I heard that there is a smart kid in ice and snow who successfully completed the arduous task of delivering the answer under the name of wifi.
It is estimated that the school was trapped by the black-hearted shielding device manufacturer! Forgot to interfere with the WiFi frequency band!
In fact, there is basically no hope that the mobile phone jammer will make the mobile phone cheat, but the cheater can also use their own communication tools. The answer seller has a special radio transmitter, and the examinee has a radio receiver (market Most of the cheating communication tools sold are of this type). The frequency band used by these illegal communication tools can be selected outside the frequency range of the cell phone jammer, and often violates the frequency band dedicated to the walkie-talkie.
For example, some candidates use built-in headphones to receive radio-transmitted exam answers. Sometimes the earphones are so small that they require magnets to suck them out, or a doctor's help to get them out. Alternatively, electronic devices such as receiving modules are hidden in the temples.
However, the road is one foot high and the devil is one foot high.
There is a radio monitor that can help with electromagnetic signals in those frequency bands that cell phone jammers can't care about. Before the start of the test, the signal strength generated by various legal radio wave devices such as mobile phones, radios, and televisions around the test room are recorded in the test room. All the signals of the entire radio wave band can be received when all the signals are activated. When the cheating tool starts to send answers to the examination room, there will be "an extra piece" of radio wave signal of unknown origin on the monitor, and the signal of the cheating tool is hard to escape. over sophisticated detector ears.
For example, the most rigorous college entrance examination in history uses drones that are used to detect signals.
When candidates cheat, when the sender and receiver communicate inside and outside the examination room, "precious information" such as ABCD answers must first be converted into binary numbers, encoded, and encrypted if necessary, and then the electromagnetic waves of the band used will be processed. Modulation, loads the information on the electromagnetic wave signal, which is sent by the antenna of the transmitter, and the other party in the examination room decodes and demodulates, and restores the ABCD information.
However, with this wireless detector, it is possible to get a clear picture of how the signals used by both sides of the cheating method transmit information within a few seconds. Say what.
No matter how sophisticated the equipment used by cheaters is, the nature of electromagnetic waves "big near and far small" must exist. By relying on multiple monitors placed in different positions, the signal can be calculated according to the distance and the strength of the signal. The position of the launcher, the answer launcher was captured on the spot.