What's the frequency in shortwave radio?

The power of short-wave radio stations is usually a few watts to several tens of watts.

There are two basic modes of short wave propagation: one is ground wave and the other is sky wave. The conductive characteristics of the sea surface medium are most conducive to the propagation of electric waves, and short-wave ground wave signals can travel about 1000 km along the sea surface; The conductivity of land medium is poor, and the radio wave attenuation is large. The radio wave attenuation of different land medium is different (the attenuation of wet land surface is small, and the attenuation of dry sand surface is large). Short-wave signals can only travel along the ground for dozens of kilometers at most. Ground wave propagation does not need to change the working frequency frequently, but it is different from sky wave propagation because of the obstruction.

The main transmission route of short wave is sky wave. After the short-wave signal is sent by the antenna, it is reflected back to the ground through the ionosphere, and then reflected back to the ionosphere from the ground. It can be reflected many times, so the propagation distance is far (hundreds to tens of thousands of kilometers) and will not be blocked by obstacles on the ground. But the sky wave is very unstable. In the process of sky wave propagation, path attenuation, time delay, atmospheric noise, multipath effect, ionospheric fading and other factors will cause signal attenuation and distortion, which will affect the effect of short-wave communication.

Compared with medium wave, short-wave radio stations are prone to crosstalk, poor indoor reception and lightning strike. Indoor electronic fluorescent lamps, SCR dimming table lamps, computers, televisions, microwave ovens and telephone lines all have interference, which is easily distorted and unstable. Therefore, China Radio still has irreplaceable advantages.