For all mobile phone users, the national college entrance examination will be held from June 7th to 8th every year. During the test, each test center will turn on the mobile phone shielding device, which will greatly affect the call quality of surrounding users, such as: frequent call failures, no connection, Interrupted calls, slow Internet access on mobile phones, etc. For the sake of the majority of candidates, please understand all friends who live near the test center! What the hell is this?
This starts with the mobile phone shielding device. First of all, our flowers were initially assumed to be dishonest bad children. Those adults thought that they would cheat in the college entrance examination and use various high-end electronic communication equipment, so they moved to the examination room isolator. Killer. It is possible to make a classroom and an examination room "isolated" from the perspective of electronic communication. At present, various communication tools use electromagnetic waves or radio waves to transmit signals. Classroom electromagnetic shielding can achieve the goal. If the classroom is tightly wrapped around it like a big cage, no electromagnetic signals can get out or come in, and all the signals sent by the mobile phone inside will be absorbed by the walls. But if this is an electromagnetic shielding laboratory, it is OK, but it is not feasible for ordinary classrooms.
The mobile phone shielding device used in the college entrance examination in the past is not the shielding device mentioned above. The principle of the mobile phone shielding device currently used in the college entrance examination is that when your mobile phone is sending and receiving information, the mobile phone shielding device acts as a super cheerleader to "shout", and the "noise signal" is so large that your mobile phone "ear" cannot hear it. Qing, the "mouth" can't even call the mobile phone shielding device. To put it simply, this is not blocking your signal (it is difficult to block the signal and requires very harsh conditions), but blocking your signal. It is to bury your useful electromagnetic wave signals in a large number of useless signals. Or you can put it this way, you are whispering to your girlfriend, and suddenly 20 foreigners come and rap loudly in 20 foreign languages at the same time, and you can't hear your girlfriend.
Because so much noise comes out, it not only "shields" the signal of the test room, but also interferes with the wireless signals around the test room, which seriously affects the call quality of mobile phone users around the test room. Therefore, once again, a warm reminder, for the flowers of the motherland, please be patient for three days. But is this shield really useful?
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" and "the five tones are incomplete". A mobile phone shielding device can only shield a small part of the frequency bands, and communication tools can use the unshielded frequency bands 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 shielding device is working, it will emit messy electromagnetic waves from low frequency to high frequency in various frequency bands, which will interfere 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! Forget about jamming the WiFi band! In fact, there is basically no hope that the test room signal blocker will make the mobile phone cheat. However, the cheater can also use their own communication tools. 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 mobile phone shielding device, 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 to deal with electromagnetic wave signals in those frequency bands that cell phone shields can't care about. Before the start of the test, the signal strength generated by various legal radio wave equipment such as mobile phones, radio, and television around the test room are recorded in the test room. All signals can be received in the entire radio wave band. 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.
Therefore, during the college entrance examination every year, it is imperative to install and use mobile phone shielding devices in each test center, which can not only purify the test room environment, prevent students from cheating, and further improve the fairness of the college entrance examination for each child.