Analysis of shortwave WAN transmission applications, what are the applications of shortwave communic

Short-wave communication is a type of radio communication, which is widely used in modern combat command. Shortwave communications propagate by sky and ground waves. Ground wave communication is stable, but in the process of propagation, the radio wave energy is constantly absorbed by the ground, the transmission attenuation is large, and the communication distance is relatively close, generally only within tens of kilometers.

Skywaves can be reflected multiple times by the ionosphere, and the communication distance can be very long. The actual short-wave communication mostly relies on skywave propagation.

In general, it is used more in military communications.

The propagation of long waves is mainly carried out by ground waves and sky waves retraced through the ionosphere, and its propagation distance is determined by the power of the transmitter and the ground situation, generally not more than 3000 kilometers. It is mainly used for radio navigation, broadcasting of standard frequencies and times, and telegraph communication, among others.

Medium waves propagate in two ways: ground waves and sky waves. In the propagation process, ground waves and sky waves exist at the same time, which sometimes causes difficulties in reception, so the transmission distance is not very far, generally hundreds of kilometers. It is mainly used for short-distance local radio broadcasting, maritime communication, radio navigation and aircraft communication.

The propagation of short waves is mainly carried out by sky waves, which can be transmitted to great distances with the help of sky waves with very little power. Mainly long-distance international radio broadcasting, long-distance wireless** and telegraph communications, radio fax, maritime and aeronautical communications, etc.

Ultra-short wave, also known as meter wave or VHF radio wave. The main mode of propagation is direct wave propagation, and the propagation distance is not far, generally tens of kilometers. It is mainly used for FM radio, television, navigation, radar and radio astronomy.

Microwaves, mainly direct wave propagation. The radiation beam of the microwave antenna can be very narrow, so the gain of the antenna is higher, which is conducive to directional propagation; Due to the high frequency and large channel capacity, the application range is also very wide. It is mainly used for fixed-point and mobile communication and navigation.

Radar positioning and velocity measurement, satellite communication, relay communication, meteorology, radio astronomy, etc.

There are two basic routes of propagation of short waves: one is a ground wave and the other is a sky wave.

As mentioned earlier, ground waves propagate along the Earth's surface, and their propagation distance depends on the properties of the surface medium. The conductivity characteristics of the sea surface medium are the most favorable for radio wave propagation, and the short-wave ground wave signal can propagate about 1000 kilometers along the coastal surface. The conductivity characteristics of the land surface medium are poor, and the attenuation of radio waves is large, and the attenuation degree of radio waves is different for different land surface media (the attenuation of wet soil is small, and the attenuation of dry sand and gravel ground is large). Shortwave signals can only travel a maximum of a few tens of kilometers along the ground.

Groundwave propagation does not require frequent changes in operating frequencies, but obstruction of obstacles is taken into account, which is different from skywave propagation.

The main propagation route of short waves is the sky wave. After the short-wave signal is sent by the antenna, it is reflected back to the ground through the ionosphere, and then from the ground back to the ionosphere, which can be reflected many times, so the propagation distance is very long (millions to tens of thousands of kilometers), and it is not blocked by ground obstacles. But the sky wave is very unstable.

In the process of skywave propagation, factors such as path attenuation, time delay, atmospheric noise, multipath effect, ionospheric fading and other factors will cause signal weakening and distortion, and affect the effect of shortwave communication.

When the ionosphere reflects the short wave back to the ground, it can achieve communication of hundreds of kilometers to thousands of kilometers, and the ground can also reflect the radio waves to the ionosphere again, and the ionosphere forms a secondary reflection, so that after the short wave jumps between the ground and the ionosphere many times, global communication can be realized. Since the median attenuation of the ionosphere is usually a dozen dB, the propagation loss is relatively small, so it is possible to achieve global communication with a transmitter of a few kW.

The entire Earth's atmosphere, which is more than 60 kilometers above the surface, is in a state of partial or complete ionization due to the ionization of neutral, atoms and air molecules by extraterrestrial rays (mainly solar radiation) called the ionosphere. The ionosphere acts as a propagation medium, causing radio waves to be refracted and reflected, scattered and absorbed, and a part of the energy is lost in the propagation medium. 3 30 kHz is the short band, it is the most suitable band to realize the ionospheric long-distance communication and broadcasting, and the skywave transmission is the use of this characteristic of the ionosphere, but because the wavelength of microwave and ultrashort wave is short and directional, so the response of the atmospheric ionosphere to this kind of wave is not ideal.

The shortwave transmission distance is long.

1. Long wave. Long waves (including ultra-long waves) refer to radio waves with a frequency of less than 300kHz and a wavelength of 1000 10000.

Long waves, which are capable of propagating in the form of sky waves or ground waves. The long-wave band has the strongest transmission ability, and among all the bands, it is most suitable for propagating in the form of a ground wave around the earth's curved surface, but the maximum distance of the ground wave propagation is not more than (3 4) thousand kilometers, so the propagation mode of the general long wave is still dominated by the sky wave.

2. Short wave. Short wave refers to radio waves with a frequency of 3 30MHz. The wavelength of short waves is short, the diffraction ability of ground waves propagating along the earth's surface is poor, and the effective distance of propagation is short.

When short waves propagate in the form of sky waves, they are less absorbed in the ionosphere, which is conducive to the reflection of the ionosphere. After a single reflection you can get a jump distance of 100 4000km. After several successive reflections from the ionosphere and the earth, the propagation distance is even greater.

3. Medium wave. Medium wave refers to radio waves with a frequency of 300kHz 3MHz. Radio communication with a wavelength of 3000 2000 meters, propagating with wireless or surface waves, the receiving field strength is very stable, and can be used to complete the medium wave can be propagated in the form of surface waves or sky waves, and can be used to complete reliable communication, such as ship communication and navigation, etc. The wavelength of 2000 200m medium and short waves is mainly used for broadcasting, so this band is also called the broadcast band.

4. Frequency modulation. FM uses VHF, which can only transmit tens of kilometers, and VHF FM is mainly used for prefectural and municipal broadcasting, or short-range communication. Of course, if you must install a VHF FM ** on the satellite, the FM can also achieve long-distance communication.

The long-wave transmission distance is long, not easy to be blocked and absorbed, and the action distance can reach thousands to tens of thousands of kilometers, and the short-wave ground wave signal can travel about 1,000 kilometers along the coast, but due to loss, the short-wave signal can only travel dozens of kilometers along the ground at most, so it can be transmitted from hundreds to tens of thousands of kilometers mainly by relying on the transmission of sky waves.

The frequency band on the radio is generally in the shortwave band, which is not a type of classification according to wavelength, but a way of modulation.

The gap between day and night is relatively large, and it can spread long distances at night and very short during the day.

If there is no relay station, of course, it is a long wave.