Short-wave communications blackout and solutions


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The development prospects of short-wave communication
Although the current emerging new wireless communication systems, short wave, the most ancient and traditional means of communication continue to be the world’s universal attention, satellite and mobile communications in the rapid development of today’s short-wave communications not only not been eliminated, is rapidly developing. The reason is: short communication distance, survivability and autonomy communication ability, low operating costs.
Short-wave communication technology development
In recent years, short-wave communications technology in the world has been considerable progress, there have been many new stations, new equipment and new technologies. Its main features are:
1, shortwave radio
HF SSB radio ever-smaller, more efficient, getting better and better performance, compatibility is growing. Digital shortwave radio is an inevitable trend.
2, short-wave antenna
Mainly to short-wave broadband antenna, omni, no “blind spots”, high-gain direction. Become smaller, increasingly efficient. Now introduced several new base station antenna and car antenna.
3, Frequency Selection
In the frequency selection, in addition to the ASAPS has been widely used frequency measurement system and the ALE adaptive frequency selection methods, has launched a full-band short-wave frequency selection system and real-time adaptive frequency management system.
4, noise cancellation
Introduced in a variety of anti-noise in mute, noise reduction methods, especially the United States recently introduced ADSP2 SGC single-ended noise reduction device can be connected in any radio station prepared to receive the audio amplifier or speakers made noise cancellation eliminate the channel’s background noise, so that the quality of shortwave radio to listen to, at or close to the FM radio listening levels.
5, group network communication
In the group of network communication, in addition to adaptive (ALE) feature of the election call networking, the foreign countries have launched a CCIR493 Digital Selective Calling system, the radio system so that each share a non-repeating ID code (4 to 6), through which a million units composed of a large class of network, and now the production of short-wave radio station in Australia, Europe, the United States produced some short-wave radio station, has been a regular feature in the whole of curing. CCIR493 Digital Selective Calling system can achieve a single call, group call, group call, send and receive text messages, send GPS location signals transmitted alarm signal to achieve short / two-way automatic dialing features such as local call.
Short-wave communications blackout and solutions
First, the short-wave transmission
Radio, radio, television, radar and so rely on radio wave propagation to achieve.
Waves in a variety of media quality and media quality of the surface of the dissemination process boundaries, due to reflection, refraction, scattering and diffraction, the propagation direction through various changes, due to diffusion and absorption of medium quality, the field strength diminishing. In order to receive the point there is sufficient field strength, must have the radio transmission, characteristics and laws, in order to achieve good communication results.
Common mode of transmission are:
Ground wave (SAW) propagation, the direct wave (line of sight) transmission, sky-wave propagation, scattering propagation.
FM wave transmission into the application of direct communication.
The basic short-wave transmission in two ways:
A, ground-wave (SAW) propagation.
B, sky-wave propagation. HF sky-wave propagation is the main communication transmission.
1, ground wave propagation
Along the interface between the earth and the spread of the air waves, called surface wave or surface wave, referred to as ground wave. Ground wave transmission shown in Figure 1-1. The main mode of transmission depends on the electrical characteristics of the ground. Ground wave propagation process, as some energy is absorbed by the earth, soon weakened, the shorter the wavelength, the faster decrease, which spread far away. But to wave the climate, and high reliability. Typically, long wave, long wave, medium wave radio communication, the use of ground wave propagation.
2, sky-wave propagation
Refers to the antenna to the sky-wave electromagnetic radiation by the sky high-altitude ionosphere back to earth after reflection or refraction of radio waves. Transmission shown in Figure 1-2.
HF sky-wave is the main route of transmission. After the short-wave signal from the antenna, reflected by the ionosphere back to the ground, and call back from the ground ionospheric reflection, multiple reflections can thus spread far apart (can be thousands of kilometers), but not ground obstruction. But the greatest weakness of sky-wave propagation is very unstable signal, handled properly will affect the communication effectiveness. With the new wireless communications technologies continue to emerge, sky-wave propagation effects of weakness on the short-wave communications are gradually being overcome.
3, the communications blackout
The above has described two kinds of ground wave and sky-wave transmission. In general, ground wave propagation distance up to 20 to 30 km, while the sky-wave reflections from the ionosphere first floor (first hop) is the shortest distance of about 80 to 100 km, 20-100 km can be seen between this period, ground wave and sky wave are out of reach, forming a short-wave communications, “quiet zone”, also known as blind spots, shown in Figure 1-3. Most communications within the blind spot is difficult. As radio antenna restrictions, there are communications blackout problem.
Second, the methods to solve communications blackout
1, commonly used methods:
First, increase the power to extend to radio wave propagation distance; the second is an effective method is to use common high-elevation antenna, also known as “overhead antenna” or “fountain antenna” to shorten the distance sky-wave landing the first jump. Elevation antenna radiation lobe is the angle between the ground. The higher the elevation, landing the first jump waves shorter the distance, the less blind, when close to 90 ° elevation angle, the blind spot is basically not exist.
Does not appear in the new antenna, we used low-frame dipole antenna close communications blackout to solve the problem, with good results.
2, three-wire antenna is no better short-wave base station antenna blind
Australia moonlight produced FD-230 series of three-wire broadband shortwave antenna, has been promoting the use of a long time in China, according to our tests and user repeatedly to reflect actual usage, tune the antenna do not take days, high gain, easy to set up, communication effectiveness good. Set the level of use, taking into account far, the NFC (the farthest of our customers through 13,000 kilometers); inverted V set up to use, implementation, close no blind communication. The antenna system is being armed police, armed forces and the Second Artillery, the public security system, air defense systems, forestry, transportation departments and other units of a large number of widely used. China has been a lot of three-wire broadband antennas imitation, but the key components of quality and performance with foreign products, there are many gaps.
3, ML-90 antenna is currently the best non-blind short-wave antenna car
For a long time, close communications blackout has been plagued by short-wave vehicle communications. People tried a variety of antennas, although there are different degrees of improvement, but can not fundamentally solve the problem. Now the company by the Australian Ke Maike invented ML-90 vehicle completely solve the electromagnetic loop antenna close communications blackout problem.
ML-90 antenna with a single magnetic ring oscillator with the new automatic day adjusted, its special structure and special tuning principles, so that the antenna radiation generates a strong vertical component of sky-wave signal to the fountain means radiation in the air, greatly reducing the ionosphere by the first a reflective floor (first hop) radio shortest distance, the distance to the nearest sky-wave propagation and ground wave propagation of the most long-distance link, which completely eliminates the close communications blackout.
ML-90 within 100 km of the antenna is not in the communications blackout, the signal level of up to 3 to 5 minutes; 600 km of the signal level of up to 2 to 4 minutes; 1000 km range of the signal level of up to 1 to 3 minutes.
4,7006 broadband soft portable radio antenna is ideal for non-blind antenna
7006 antenna structure compact, portable, quickly set up and collection. No day adjusted, 2 ~ 30MHZ range can sound with harmonic. For individuals to carry radio, radio, outdoor temporary base station. It’s all up to the communication radius of 1,000 km at 600 km range capable of reliable communications.


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