General measurement standards for public electromagnetic radiation
1. Power density standard
Power density refers to the radiation power received per unit area, which measures signal strength and can be represented by electric field strength and magnetic field strength, but power density is more commonly used. The following figure shows the regulations on public exposure limits in the current national standard "Electromagnetic Environment Control Limits" (GB8702-2014) in China. The frequencies of mobile phones and base stations fall within the range of 30MHz to 30000MHz.
Public exposure control limits
The peak power of mobile phones is 2W, and the IEEE does not consider safety issues with transmission power below 7W. The Federal Communications Commission (FCC) of the United States has set a radiation limit of 6W/m2 for mobile phones in the 900MHz frequency band, which is 15 times more relaxed than China's 0.4W/m2.
The current electromagnetic radiation limitation standard in our country is one of the strictest international standards, which is the basis for the establishment of communication companies and inspections by the Ministry of Environmental Protection. The Ministry of Environmental Protection has supervised and tested thousands of base stations, and the results showed that for a base station with a radio frequency power of 20 watts, the power density 10 meters away from the antenna is 0.006W/m2, far below the strict Chinese limit standards.
The public panic over electromagnetic radiation from mobile phones and base stations is closely related to operators. When promoting CDMA mobile phones, a certain operator used the pseudo concept of "green phones", using low radiation as a selling point and deceiving the public to improve competitiveness. In fact, the radiation power of CDMA mobile phones is not smaller than GSM. GSM mobile phones have a peak power of 2W, and in actual use, they only transmit for 1/8 of the time, so the maximum average power is 250mW. However, CDMA is a continuous transmission, and the maximum average power is also about 250mW, with little difference between the two.
Although the maximum average power of both GSM and CDMA mobile phones is around 250mW, the actual transmission power will be much lower than this level, due to the automatic control mechanism of the base station on mobile phone power. Due to the different distances between the mobile phone and the base station, the mobile phone emits the same power. As a result, the base station receives a stronger signal power from nearby mobile phones and a weaker signal power from distant mobile phones. The mobile phone itself does not know the distance to the base station. At the beginning, it will use maximum power transmission. After receiving it, the base station will send instructions to gradually reduce the transmission power to the mobile phone. Within one second, it will send dozens to hundreds of instructions. The mobile phone in close proximity will adjust the transmission power to a very low level in a very short time, such as 0.02W.
Now operators have paid the price for the radiation rumors. In some places, base stations are difficult to enter the community, and residents are driving them away everywhere. The trick of disguising base stations as light poles and big trees is also ineffective. The operator is promoting under the false green banner, which is a typical case of drinking a dove to quench thirst.
