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In the streets of the city and the roofs of farmhouses in the suburbs, we can often see large and small "pots". Do not underestimate these "pots". Local people rely on it to watch TV. In fact, it is an antenna used to receive satellite TV signals. However, it also receives satellite signals, mobile phones andJiangmen vehicle navigatorWhy not demand this kind of "pot"?

Pot antenna

Life is inseparable from satellites

The principle of GPS navigation is as follows. It obtains the interval between the receiver and the satellite by measuring the round-trip time between the receiver and the satellite with clear azimuth, and then obtains the accurate azimuth of the receiver through the data of four or more satellites for positioning and navigation. Because the satellite TV signal is transmitted by a specific satellite synchronized with the earth, and is far away from the earth, the transmission data is more complex, so TV users need "pot" ability to get enough signals to make the TV picture output clearly. The GPS satellites are close to the earth and the transmission of data is simple, so there is no need to use a "pot".

Communication satellite

The "enemy" of radio communication

There are three ways of transmitting radio waves: sky wave, ground wave and wave transmitted along a straight line.

Ground waves are radio waves transmitted along the earth's surface space. There are various obstacles on the surface, which can be bypassed only with a longer wavelength, so long wave, medium wave and medium short wave can bypass the obstacles well. There will be energy consumption in the transmission process of ground wave. The transmission interval between medium wave and medium short wave is short, generally within hundreds of kilometers. The distance of long wave transmission along the ground is much longer, but the equipment required for long wave transmission is huge and the cost is high, so long wave is rarely used for wireless broadcasting, but mostly used for long-distance radio communication and navigation.

Sky waves are radio waves transmitted by the reflection of the ionosphere. The earth's ionosphere is in the atmospheric airspace at an altitude of 85 km to about 600 km, where the atmosphere is thin. Experiments show that microwave with a wavelength less than 10 meters can pass through the ionosphere, and waves with a wavelength greater than 3000 kilometers will be fully absorbed by the ionosphere. Therefore, short wave is the best band to use the ionosphere. Through multiple reflections of the ionosphere, electromagnetic waves can transmit more than 10000 kilometers.

Microwave and ultrashort wave travel in a straight line. Because the earth's surface is spherical, in order to increase the transmission interval, microwave transmitting and receiving antennas are built very high, even if they can only reach tens of kilometers. In long-distance communication, it is still necessary to establish relay stations, but now satellites can be used to transmit microwave. Because communication satellites are about 36000 kilometers above the equator, they can make radio signals cross continents and oceans.

Sunspot

Sunspot活動時會向外發(fā)射帶電離子，當帶電離子進入電離層時會與大氣分子發(fā)生猛烈磕碰，使電離層電子密度添加，這就會攪擾到電離層對電磁波的吸收和反射，使得無線電波信號被吸收，導致無線電波信號通過這一空間后會虛弱乃至消失。所以說在太陽黑子活潑的時候會影響地球的無線電通訊。

文章源自Jiangmen vehicle navigatorhttp://www.t2nupai.cn