Radio Waves Are Transmitted
The propagation of radio waves, because of the different wavelengths have different propagation characteristics, divided into ground wave, sky wave and space wave three forms.
Ground wave - A radio wave that spreads out of the Earth's surface space. Medium and long waves are spread by way of wave.
Sky waves - Radio waves that rely on the reflection of the ionosphere are called waves. Shortwave use this way to spread.
Space wave - A radio wave propagating along a straight line. It includes a direct wave that directly reaches the receiving point from the firing point and a reflected wave that is reflected by the ground to the receiving point.
A long wave is a radio wave with a frequency of 300 kHz or less. Since the ionosphere in the atmosphere has a strong absorption effect on the long wave, the long wave mainly travels along the earth's surface, and its propagation loss is small and the diffraction ability is strong. The frequency of less than 30kHz long wave, can spread around the globe for the world. Long wave propagation, with the stability of the spread, affected by the impact of small atmosphere and other advantages. In the sea water and soil transmission, absorption loss is also small. As the long wave requires a large antenna equipment, China's radio stations do not use long-wave (LW) band, domestic radio generally do not have long wave (LW) band. Long band is mainly used for transmission standard time signal, polar communication and maritime navigation.
Medium wave refers to the frequency of 300kHz ~ 3MHz radio waves. It can rely on ionospheric reflection of the form of the spread of the waves, but also reliable along the Earth's surface wave propagation. During the daytime, due to the large absorption of the ionosphere, the sky wave can not be effectively reflected, mainly by ground wave propagation. But the absorption of the ground wave is stronger than that of the long wave, and the medium wave diffraction ability is shorter than the long wave, and the propagation distance is shorter than the long wave. For medium-power radio stations, the wave can spread around 300km. In the evening, the absorption of the ionosphere decreases, which greatly increases the propagation distance. Radio frequency in the radio frequency (MW) frequency range of China's provisions for the 535 ~ 1605kHz, so the domestic radio in the wave (MW) to receive the frequency range of 535 ~ 1605kHz.