The use of the platform antenna and its radiation hazard

The use of radio transceivers will inevitably suffer from electromagnetic radiation. Although the degree of influence of electromagnetic radiation on human health is still unclear, it is undeniable that when electromagnetic radiation exceeds a certain intensity, it will cause harm to the human body, resulting in physical fatigue, headache and insomnia. , memory loss, abnormal blood pressure, decreased immune function.

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The basic function of the antenna is to convert the high-frequency current carrying the sound information into electromagnetic waves and radiate it out into the air during transmission. When receiving, the electromagnetic waves in the air are converted into high-frequency current and sent to the internal circuit of the vehicle for processing to finally obtain the sound information. Its performance has a great impact on the overall technical indicators. Be sure to read the service manual carefully after buying the car, to understand the product's power, frequency, sensitivity, working methods and other performance indicators. And select the appropriate antenna accordingly. Before installing the antenna, first test the connector, feeder and base with the multimeter resistance file to ensure that there is no open circuit short circuit fault. If there is an open circuit or short circuit, it must not be transmitted. Otherwise, the transmission power will be totally reflected into the vehicle platform, which will easily burn the final power. Amplify the circuit, causing economic losses. If there are conditions, it is best to test the antenna related indicators with a frequency sweeper, antenna analyzer, etc.

There are four indicators that determine the performance of the platform antenna: maximum withstand power, center frequency, bandwidth gain, and standing wave ratio. Under normal circumstances, the first indicator does not need to be considered, because the maximum power of the platform antenna is more than 100W, which is much larger than the maximum transmission power of the platform. The latter three indicators are closely related to each other. The center frequency refers to the optimal resonant frequency when the antenna is working. If it works at this frequency, all the transmitting power of the vehicle will be converted into electromagnetic waves by the antenna, that is, the antenna. The standing wave ratio is 1 (ideal state), and the VSWR is gradually increased from the center frequency. When the standing wave ratio is gradually increased to 1.5 (the power reflection reaches 4%. The width between the upper and lower frequencies is called the antenna. The working bandwidth and bandwidth depend on the external form of the antenna, the materials used, the quality factor and the gain. The higher the gain, the narrower the bandwidth, which will exceed the frequency range. The effective transmit power and receiving sensitivity of the vehicle are It will drop sharply. When the standing wave ratio is greater than 2 (power reflection reaches 11.1%), it is recommended to stop the launching of the platform, otherwise it will endanger the safety of the equipment. The center frequency and bandwidth gain of the platform antenna are fixed at the factory and are usually clearly marked on the package or on the nameplate. However, the standing wave ratio of the antenna is not certain, and it is closely related to the actual installation position of the antenna.

In theory, the most ideal mounting position for the car antenna is the center of the roof. The antenna is attached to the roof by a magnetic chuck. Although it is usually insulated from the metal roof, there is no difference between the two. The capacitor forms a path in the high frequency state, and the roof is used as the ground network of the antenna feeder system, and the antenna together constitutes the antenna system of the vehicle radio. However, in real life, it is limited by various external conditions, such as the long-term influence of the antenna into the garage. In addition, in order to prevent the paint from being scratched, bumping or falling off, or using a large, heavier antenna with high gain, the vehicle antenna often It is not installed in this position, but is installed on the luggage rack, spare tire frame, front and rear guard bars, side frame, trunk lid and even exhaust pipe of the car with stainless steel steel seat, and even more directly into the car. Inside. Changing the position of the antenna actually changes the ground network of the antenna system, and the standing wave ratio naturally changes. In addition to the center of the roof, can the antenna be adjusted to the ideal working condition at other locations? The answer is yes, as long as the VSWR power meter (ie SWR meter) is used for installation, or the antenna tester is used directly, and the selected position is adjusted while measuring to ensure that the antenna standing wave ratio is less than 1.5, it can be placed on the roof. Any place other than.

The use of radio transceivers will inevitably suffer from electromagnetic radiation. Although the degree of influence of electromagnetic radiation on human health is still unclear, it is undeniable that when electromagnetic radiation exceeds a certain intensity, it will cause harm to the human body, resulting in physical fatigue, headache and insomnia. , memory loss, abnormal blood pressure, decreased immune function. If you receive high-intensity electromagnetic radiation for a long time, it will cause cataracts, miscarriage of pregnant women, and even cancer, especially sensitive people such as the elderly, children, pregnant women or patients with pacemakers. Since the current transmission power of VHF or UHF car radios is about 20 to 50 watts (more than a dozen milliwatts to 2 watts of mobile phone transmission power), the radiation hazard will rise, and we must not take it lightly. Of course, under normal circumstances, the antenna is placed outside the vehicle. Due to the electromagnetic shielding effect of the metal casing of the automobile, the radiation of the vehicle platform to the human body complies with the requirements of the national electromagnetic radiation protection regulations. However, if the antenna of the vehicle is taken into the vehicle, the ground wave of the antenna system is destroyed, and the standing wave ratio will become very high. Most of the transmitted power is reflected back to the platform, and the effective transmission power is drastically reduced. The external shielding effect of the carriage will significantly worsen the launching effect. Especially the antenna is too close to the human body, and the electromagnetic waves are reflected back and forth in the cabin. The electromagnetic wave density will greatly exceed the hygienic safety standards, causing the electromagnetic radiation of the human body to be intensified. Therefore, for the sake of health and safety, all forms of electromagnetic wave emission should be avoided in the car.