We most often use radio waves, whose frequency ranges from 3kHz to 3000ghz. In order of frequency from low to high, 3kHz to 30kHz are very low frequency, and VLF is the abbreviation of very low frequency. Then, as shown in the figure, it goes to the right and so on. The frequency is higher and higher, and the wavelength is shorter and shorter.

An interesting difference is that foreign countries are usually divided by frequency, while China is usually named by wavelength. For example, foreign countries will say VLF, while China will say it is a very long wave. In fact, the meaning is the same. They all refer to this spectrum. In order to effectively radiate energy, the length of the antenna is directly proportional to the wavelength, usually 1 / 4 of the wavelength, and the shortest can not be less than 1 / 10, and then the signal can be effectively radiated.