What is the wavelength of short wave communication?

1899 In March, Marconi successfully conducted an experiment to make radio waves cross the 45-kilometer-wide English Channel. At that time, Marconi used medium wave, the wavelength was 1000 ~ 100 m, and the corresponding frequency (i.e., the fluctuation number of 1 s) was 300 ~ 3000 kHz. Medium wave is one of the earliest bands used by people, which is mainly used for broadcasting, navigation and communication.

The wavelength of short wave is 100 ~ 10 m, and the corresponding frequency is 3 ~ 30 MHz. The application of short wave quickly surpassed that of medium wave because of its long distance, economy and convenience. 192 1 year, human beings realized the transoceanic propagation of short waves for the first time. This pioneer is not a famous expert, but an unknown amateur radio enthusiast's accidental discovery.

192 1 year, a fire broke out in the suburbs of Rome, Italy. An amateur short-wave radio station with a power of only a few tens of watts sent out a distress signal in order to let nearby firefighters come to the rescue quickly. Unexpectedly, this distress signal was received by some receivers in Copenhagen (the capital of Denmark) 500 kilometers away from/kloc-0. Of course, it is not helpful for the fire fighting in Rome, but this discovery has aroused the interest of many radio enthusiasts and attracted the attention of some scientists, who have conducted similar experiments respectively. The experimental results show that short wave is more suitable for long-distance communication than long wave, so some countries have gradually established short wave communication lines. In 924, the first short-wave communication line was established between Nauen in Germany and Buenos Aires in Argentina.

Scientists have found that radio waves can bend around the earth because there is a charged particle layer in the atmosphere, which is produced by ionizing the air in the atmosphere by the ultraviolet rays of the sun. 1924, the British physicist appleton, with the assistance of Banert, directly measured the height of the charged particle layer, and confirmed for the first time that there was a charged particle layer at the height of110 ~120m above the ground. The existence of this charged particle layer was first proposed by kennelly, an American communication engineer, and Hevisai, an English electrical engineer, at the beginning of the 20th century. Now this hypothesis has been confirmed by experiments, so it is called kennelly-Hevisai charged particle layer, also called E charged particle layer. 1926, appleton discovered that there was also a charged particle layer at a height of 200 ~ 400 meters from the ground. People call it appleton charged particle layer, also called F charged particle layer. Because of appleton's outstanding contribution, he won the 1947 Nobel Prize in Physics. 1930, the British physicist Watson Watt officially named these charged particle layers in the upper atmosphere "ionosphere". For example, the e charged particle layer mentioned above is called the e ionosphere; F charged particle layer, called F ionosphere.

After long-term exploration, people gradually realize that the mid-band electromagnetic wave mainly reflects between the positive ionosphere and the ground and propagates far away. However, short-wave electromagnetic waves are mainly reflected between the mine ionosphere and the ground, and spread to a distant place. Obviously, the distance of short wave propagation is much farther than that of medium wave propagation.

Radio communication with short wave is called short wave communication, which mainly relies on sky wave and ground wave to spread. Sky wave propagation depends on the reflection of F ionosphere, and the propagation attenuation is small. Therefore, long-distance communication and broadcasting can be carried out with less power and lower cost. Short-wave broadcasting is still the main means of international broadcasting, and short-wave frequency band is also the common frequency band of modern amateur radio communication.

1938, the former Soviet union built a short-wave radio station with the power of 120 kW, which was the most powerful radio station in the world at that time.

The appearance of short-wave communication in the 1920s changed the historical process of the development of radio communication.