During the exam period today and tomorrow, as a melon eater, you may not only feel the congestion and quietness when passing by the school, but the mobile phone signal may be poor. At this time, you must not resent the operator. The reason is as shown in the figure below. tell.
As a candidate during the exam, you found a router-like device when you walked into the exam room. Don't be "excited" to be able to "surf the Internet", it may be a "mobile phone signal jammer".
Today is during the exam, and I want to talk to you about communication interference.
The frequency range of China Mobile Unicom Telecom
When the communication technology was still in the 2G era, the "mobile phone signal jammer" could work perfectly. At that time, the frequency bands used by most operators were relatively fixed, the bandwidth was also narrow, and interference was relatively easy.
As can be seen from the above figure, in mobile communication technology, 2G mainly works in the frequency band around 900/1800MHz, 3G works in the 1900-2100MHz frequency band, and 4G works in the 2300-2500MHz frequency band.
With the rapid development of communication technology, the development of 3G and 4G communication technology has made the "signal jammer" encounter a dilemma. The signal interference originally designed only for 2G, because of the frequency, cannot cover the 3G and 4G signals, which will cause the shielding to be ineffective.
Fortunately, signal blockers are also developing, and soon there will be interference functions specifically for 3G and 4G frequency bands, which can block these three frequency bands at the same time and space.
The principle of mobile phone signal jammer
The mobile phone signal jammer scans from the low-end frequency of the forward channel to the high-end at a certain speed during the working process, the transmission power is in the order of several watts, and the shielding range is adjustable, generally tens of meters. The garbled interference is formed in the signal received by the mobile phone, so that the mobile phone cannot detect the normal data sent from the base station, and the mobile phone cannot establish a connection with the base station. It is manifested as the phenomenon of searching the network, no mobile phone signal, no service system, etc.
Different working systems of mobile phones have different coding methods or different modulation methods, and their information amounts are different. According to Shannon's formula, their signal-to-noise ratio requirements are also different, and their sensitivity requirements are also different.
Modern communication technology adopts advanced anti-jamming technologies, such as frequency hopping, direct sequence spread spectrum (DSSS) and other technologies, but the suppression of interference by frequency hopping and spread spectrum mainly relies on intermediate frequency filtering. However, due to the front-end high-frequency amplifier and mixer They are all non-linear devices, which will produce intermodulation interference and noise deterioration when there is strong interference, that is, block the radio frequency front end.
In addition, there are many technologies for communication interference, such as broadband noise interference, noise interference in some frequency bands, multi-tone interference, frequency sweep interference, tracking interference, smart interference and so on. The mobile phone signal jammer only needs to ensure that the communication signal is shielded in a certain small range, so it is generally easier to interfere as long as the frequency band can be covered.
More Challenges for Blockers
Don't think that "everything will be fine" if the cell phone signal is blocked! I heard that someone has used the "WIFI name" to complete the delivery of the answer. It seems that the development of the jammer can't relax for a moment, let's see if we want to upgrade to the 5GHz band! There are also reports of home-made illicit devices that transmit and receive radios, maliciously using frequency bands not covered by the jammers.
Mastering the stick, but aiming for the yard!
There are reports that drones can be used with radio detection equipment to record and "decode" signals, and even locate the source of the transmission to directly capture the sender of the answer.
There is no good or bad technology, but the consequences are good or bad, such as communication, radar, and jamming and anti-jamming technology!
The exam period is a key point in life. What we should do is to hold the correct beliefs and proper methods, and put an end to the fluke. The development of technology should be used to benefit human beings and maintain world peace, not for the sake of temporary self-interest. Only a solid knowledge reserve can make you really calm and worry-free.