Examination room signal jammer, in-depth analysis of knowledge

　　This is because the teachers thought that the students would cheat in the college entrance examination, and they would also use various high-end electronic communication equipment, so they brought in the killer of the signal shielding device.

　　Although a mobile phone is a wireless communication device that is used wherever we go, there is also an invisible wire dragging it, that is, the mobile phone base station. Whether making a phone call or answering a phone call, the first step is to establish contact with a nearby cell phone base station. If you hold a mobile phone in your left hand and right hand, and use the mobile phone in your left hand to dial the mobile phone in your right hand, the electromagnetic wave of the mobile phone is not as simple as passing directly from the left hand to the right hand, but will travel a long way from the left hand phone to hundreds of meters away. Mobile phone base station, and then take a big circle and send it back to the right-hand mobile phone (except for Bluetooth function). Normally, the base station brother and the mobile phone brother are chatting in full swing. The radio wave signals sent by the two parties come and go, but when the shield is turned on, it will "beat gongs and drums" around the mobile phone, sending out more power than the received base station signal. Many times the "noise" radio wave signal, the mobile phone can not hear what the base station is talking about, cannot receive the signal from the base station normally, and the connection between the two is cut off, the mobile phone will become an island, regardless of making calls, sending text messages or other various functions , Are in a state of paralysis.

　　Therefore, operators have to issue warm reminders. Because so much noise comes out, not only the signals in the examination room are "shielded", the wireless signals 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 will complain, and of course the operator will be anxious. However, the operators can’t really be blamed for this! So, once again, warm reminder, for the flowers of the motherland, please bear with me for three days.

　　Is this shield really useful?

　　The entire frequency band of electromagnetic waves ranges from the smallest a few Hz to the largest hundreds of GHz, and each segment may be used as a communication signal, but except for a few very professional equipment, ordinary shields are all "The voice is not loud enough" and "the five sounds are not complete". A jammer can only shield a small part of the frequency bands, and communication tools can use unshielded frequency bands for communication. Of course, all the 2G, 3G, and 4G mobile phone services of several domestic communication companies are concentrated in a few small frequency bands. The shielding device in the examination room can still focus on these frequency bands. When the mobile phone jammer is working, it will send out chaotic 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 a smart kid with ice and snow successfully completed the arduous task of delivering answers using the wifi name.

　　This is probably because the school was pitted by the black heart shielding device manufacturer! Forgot to interfere with the WiFi frequency band!

　　In fact, it is basically hopeless that mobile phone jammers will allow mobile phones to cheat, but cheaters can also use their own communication tools. Most of the cheating communication tools sold are of this type). The frequency bands used by these illegal communication tools can be selected outside the range of the mobile phone jammers, and they often violate the frequency bands dedicated to walkie-talkies.

　　For example, some candidates use built-in earphones to receive test answers transmitted by radio. Sometimes, this kind of earphone is so small that it needs a magnet to suck it out. If it doesn't, it needs the help of a doctor to take it out. Or, electronic devices such as the receiving module are hidden in the temples of the glasses.

　　However, the road is one foot high and the devil is one foot high.

　　There is a radio monitor that can help fix the electromagnetic wave signals in those frequency bands that the mobile phone jammer does not take care of. Before the start of the test, the signal strength generated by various legal radio wave devices such as mobile phones, radios, and TVs around the test room are recorded in the test room. After the test starts, in the car, suitcase, and office radio monitors. Start all together, you can receive all the signals of the entire radio wave frequency band. When the cheating tool starts to send answers to the examination room, there will be "an extra piece" of radio wave signals from an unknown source on the monitor. The signal from the cheating tool is difficult to escape. Through the ears of a sophisticated detector.

　　For example, the most rigorous college entrance examination in history used drones that bombed the sky to detect signals.

　　When the examinee cheats, when the sending and receiving parties inside and outside the examination room communicate, the “valuable information” such as ABCD answers must first be converted into binary numbers, encoded, and encrypted if necessary, and then the electromagnetic waves of the used band will be processed. Modulation, the information is loaded on the electromagnetic wave signal, which is sent out 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, the signal transmission method used by both parties of the cheating technique can be clearly understood within a few seconds. Not only the signal is detected, but the information inside can even be extracted directly and heard in the conversation. Say what.

　　No matter how sophisticated the equipment used by the cheaters is, the nature of electromagnetic waves "near big and far small" must exist. Relying on multiple monitors placed in different positions, the signal can be calculated based on the distance and the strength of the signal. The location of the launcher, capture the answer launcher on the spot.

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