First, the middle wave
The propagation of the medium wave is mainly affected by the ionosphere, and the medium wave station received at night will be more than during the day. This is due to the different changes in the conductivity of the ionosphere during the day and night. During the daytime, due to sunlight, the density of the ionosphere increases, the conductivity is enhanced, and the absorption of electric waves is also large. A large part of the medium wave is absorbed and spreads not far; at night, the atmosphere is not exposed to the sun, and the ionosphere has a large electrical conductivity. If it is weakened, the medium wave can be transmitted to a long distance through the sky wave path. Therefore, it is best to listen to the medium wave station at night.
Second, short wave
The reception of medium wave broadcasting from the transmitting antenna of the radio to the radio is generally within a few hundred kilometers in diameter, and the medium wavelength is relatively long and is not easily affected by obstacles such as buildings. The distance from the short-wave transmitting station to the receiver is often thousands of kilometers or even tens of thousands of kilometers. The transmitting antenna of the radio station also has a certain direction and elevation angle. It is easily affected by the atmosphere and obstacles during the propagation process.
The main route of transmission of short waves is the sky wave. After being sent by the antenna, the short-wave signal is reflected back to the ground by the ionosphere and reflected back to the ionosphere by the ground. It can be reflected many times, so the propagation distance is very long (hundreds to tens of thousands of kilometers) and is not blocked by ground obstacles. The ionosphere over the earth is like a multi-faceted mirror. Its ability to reflect short-waves, its height is changing at any time, so short-wave broadcasting becomes unreliable. In the process of sky wave propagation, path attenuation, time delay, atmospheric noise, multipath effect, ionospheric fading and other factors will cause signal weakening and distortion, affecting the effect of short-wave communication.
Even so, there are some changes in the ionosphere that can be generalized, because the main factor in the formation of the ionosphere is ultraviolet light from the sun, which has stronger energy, and the penetration of the atmosphere can ionize certain gas molecules. The energy causes the charge ions in the gas molecule to be depleted of electrons and the remainder of the positively charged electrons to become free positive ions, and the ionized gas layer is the ionosphere. In this way, intercontinental services can be realized. Driven by many factors, the ionosphere is also affected by the following factors:
1. The strength of solar activity: the so-called change of about one cycle every 11 years.
2. The distance between the sun and the earth: that is, changes throughout the year.
3. The thickness of the atmosphere through which solar energy is transmitted to Earth: the change from morning to dusk to night during the day. After the ionosphere is affected, the short-wave reception is not normal. With the change of day and night and the season, the short-wave reception often has a sound similar to the waves, which is a common phenomenon of listening to short-wave, although today's electronic circuit utilization Automatic gain (AGC) is used to eliminate this phenomenon, but it cannot be completely eliminated. In the worst case, the sound will still be big and small.
In addition, if the living place is a steel structure building or a high-rise building around, the broadcast signal is shielded from a part, and the indoor signal will be much weaker than the outdoor. Therefore, the best way to listen to the short wave is: the rod antenna of the radio outside. Listen; use the radio while indoors, or near the window, or use an outdoor antenna to improve reception.
Third, FM
The powerful VHF TV broadcast and the radio waves of the BB transmitter will interfere with the FM reception. In addition, several FM stations with high frequency adjacent and strong transmit power will also interfere with each other. Therefore, when receiving a strong interference signal, the rod antenna should be shortened, the antenna direction should be changed, the listening position should be changed, and the interference level should be minimized.
In addition, televisions, fluorescent lamps, thyristor dimming lamps, computers, car engines, electric motors and other electrical equipment and other signal transmitters will also cause some interference to the radio signal reception. When using the radio, keep the above equipment. a certain distance. Do not use an external antenna during thunderstorms!
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