What Is a Shortwave Band?

Shortwave refers to radio waves with a frequency of 3 to 30MHz. Short wavelengths have short wavelengths, poor ground wave diffraction capabilities propagating along the surface of the earth, and short effective distances for propagation. When short waves propagate in the form of sky waves, the absorption in the ionosphere is small, which is beneficial to the reflection of the ionosphere. After one reflection, a jump distance of 100 to 4000 km can be obtained. After several consecutive reflections from the ionosphere and the earth, the propagation distance is further.

The high-frequency part of the radio frequency spectrum, with a frequency of 3 to 30 MHz, is sometimes called a short-wave band. According to current standards, this is a misnomer because its wavelengths are longer than high-frequency, microwave, and infrared, and they are often used in wireless devices. In free space, a frequency of 3 MHz corresponds to a wavelength of 100 m; 30 MHz corresponds to a wavelength of 10 m. Shortwave got its name in the early days of radio technology. At that time, the radio wavelength of 3 to 30MHz was shorter than the wavelength of most broadcast and communication signals (on the order of kilometers).

Anyone can build or buy a short-wave or ordinary-band radio, and then install a general outdoor antenna to listen to signals from all over the world. This hobby activity is called Short Wave Listening (SWL). In the United States, the prosperity of computers and online communications has surpassed short-wave listening to a certain extent. Many young people who are growing up now know nothing about this field of broadcasting and communications. way of communication. However, some people are still fascinated because people can communicate with each other using only wireless devices. In addition to the need for two antennas (located on both sides of the communication), no other artificial facilities are required. The ionosphere can return short-wave signals to the earth's surface. This feature can provide global broadcasting and communication, which is the same as it was in the early 20th century (when wireless communication was born). ^[1]

There are two basic propagation paths for short waves: one is

The short-wave band is very wide, and the radio signals are also scattered. Acceptance requires certain skills.

1. Need a good receiving environment and a sensitive radio. A good acceptance environment can be open areas, high-rise roofs, and other places that are not blocked. In the room, especially in the reinforced concrete building, the receiving effect is very poor due to the shielding effect, and there are many disturbances. In addition, the radio needs to pull out the antenna when receiving short waves. Of course it is better if you have a separate outdoor antenna.

2. Find out the transmission time and frequency of the shortwave station. These can be obtained from the Internet, you can go to the broadcasting forum, there is a shortwave frequency table in the BCL area. Generally 19-meter, 41-meter and other band broadcasts are more concentrated. Or listen to these bands at will, and you can hear the strong folk music at the BBC VOA frequency. (Like our great party. Another whisper, really want to listen to the radio broadcast of these stations should carefully search the entire band, sometimes these stations will change the frequency, and these frequencies do not appear on the frequency table. If the radio by 18000 (Receiving frequencies above kHz can be searched between 18,000 and 23,000 kHz.)

3. Tuning of short wave. Be slow and patient! The mid-wave band is from 535 to 1605 kHz, while the short-wave band is 2700 to 18000 kHz, with one station every 9 kHz (though this is not the case, this is only a theoretical requirement), it is easy to know from the coverage situation. The position of each radio station on the short-wave band is very small. Although the radio divides the short-wave band into many areas (1234567890) for easy tuning, you still have to be careful and careful. Slowly turn the tuning handwheel. When listening, if you hear a sound similar to the broadcast, carefully turn the tuning handwheel left and right, and listen carefully to the broadcast sound to obtain the correct tuning.

4. Be mentally prepared. For ordinary radios, the sound quality of short-band radio broadcasts cannot be compared with FM or even medium-wave. And the short-wave propagation is far less stable than the mid-wave due to ionospheric fluctuations. There will be strong and weak fading. Although the radio has automatic gain control, it cannot be completely eliminated.