Discussion on the uncertainty of equipment power and shielding distance (range, area)
Several parameter questions that are helpful to the shielding effect:
1) Output power
①The output power of the shield
②The performance of the antenna radiation (the gain, directivity, etc. of the antenna)
2) How Shielding Works
Nowadays, mobile phones are all digital signals, and digital signals have strong anti-interference ability. Generally, analog signal technology is used to interfere with digital signals. Therefore, digital signals must be used to interfere with digital signals. The interference effect is very different. The jammer using digital interference signal technology has lower power and higher efficiency than the jammer using analog signal interference technology.
3) Indoor and outdoor are not the same
The analysis of synthesis, attenuation and reflection of indoor mobile phone signals and interference signals is very complicated.
4) Before shielding, the strength and quality of mobile phone signals in the local space have a great impact on shielding. Different mobile phones have different effects. Generally, mobile phones with strong ability to receive weak signals may not have good anti-interference effects.
5) The direction of the base station and the direction of the shielded area of the mobile phone also affect the shielding effect.
6) The characteristics of shielding distance and radio signal transmission distance. Now, the shielding distance is briefly discussed in terms of the attenuation of radio signal transmission in free space. According to the transmission theory formula, every time the radio wave transmission distance doubles, the signal strength is attenuated by 6db (the signal power is reduced by 4 times. ). Then we take a cell phone jammer GSM 900MHZ as an example. If the mobile phone signal strength of a certain area to be shielded is -50dbm, the effective shielding distance of the jammer is 10 meters, and the change of the mobile phone signal strength will directly affect the shielding distance.
The relationship between signal strength and distance
Note: dbm is the abbreviation of dbmw, which represents the power strength unit of radio equipment or signal, that is, decibel milliwatts
①Generally, the signal strength in space is about -60 to -70dbm, and the maximum can reach about -40dbm within a few hundred meters of the base station. The mobile phone reception strength range is generally between -35 and -95dbm.
②The higher the power of the mobile phone signal in space, the shorter the shielding distance.
The above discussion is based on the conclusion that radio signals are transmitted in free space (the so-called free space is similar to space). In reality, there are many obstacles on the ground that affect the transmission of radio waves. The above conclusions can only be used as a qualitative reference, especially The above rules are very different from the actual indoors. Therefore, this problem is difficult to calculate accurately at the moment, and can only be determined according to the actual situation on site. Precise construction projects must carry out preliminary research and signal testing, and then design specific solutions. In the later stage, timely follow-up tests are required, and certain corresponding supplements can be made to be foolproof, that is, to achieve the effect of strict shielding. For example, to interfere with someone's language, how loud can you use to interfere with the audience's volume, speech intelligibility, indoor echoes, and the distance between the speaker and the audience and the interfering person are also related.
7) Due to various reasons, it is not within the scope of this article, please understand.