Frequency: The transmitter of a broadcasting station is the motive force for generating radio waves, where the current first oscillates back and forth very quickly, that is, it oscillates, and after amplification and processing by the transmitter, the signal is strong enough to be transmitted to the antenna of the tower. This is where the actual radio waves are generated. Referring to Figure 1, the curve represents the relationship between intensity and time. The radio wave is generated by the electrons flowing along the antenna. If the left side of the curve is the starting point, we can see that the curve gradually rises from the zero point and then returns. Zero point, which means that the current is on the antenna, the radio wave generated from one end to the other end, and when the current runs back from the other end, it produces a curve below the zero point baseline, which is a cycle. The curve like Figure 1 is the frequency of radio waves. For example, a certain MW station is 1,000,000 cycles/second, but people usually used to reduce it to 1,000 kilohertz (KHz). KHz is the abbreviation of Kilo Hertz. Chinese is called kilohertz, which means One thousand cycles, but the frequency in the short wave band is usually higher (3000-30000 kHz). In order to facilitate reading and writing, the short wave frequency is usually expressed in MHz (MHz). MHz is the abbreviation of English Mega Hertz. In many cases, Both mix KHz and MHz, so it is best to distinguish the meaning of these two different units and their conversion. To convert KHz to MHz, just move the decimal point forward by three bits.

E.g： 

5900 KHz = 5.9MHz 18000KHz = 18 MHz 1 MHz = 1000 KHz = 1000，000 Hz Note: For FM radio, in order to facilitate reading and writing, it is also expressed in MHz (MHz). 

Wavelength: Another name often heard in short-wave broadcasts is the "(m) band" or "meter band", which refers to the wavelength, that is, the distance between one cycle of the wave transmitted from the antenna. . Assuming that the radio wave in Fig. 2 is 15 MHz, its wavelength refers to the distance from point A to point B. If the number of cycles per second doubles, it becomes 30MHz, which is Figure 3. Looking at the waveforms of Fig. 2 and Fig. 3, it can be found that 15 MHz has two cycles of 30 MHz per cycle, that is, the higher the frequency, the shorter the wavelength. 

Frequency vs. Wavelength and Conversion: How do you convert a wavelength into a frequency, or do the opposite? Although a station broadcasts at a fixed frequency, "wavelength" is often used. For example, when describing short-wave conduction conditions, using the 31(m) band is much simpler than using "9500KHz to 9900 kHz/KHz" (this is the frequency range planned for international short-wave broadcasting in the 31(m) band). . The formula for converting the frequency into wavelength is wavelength ((m)/meter) = 300,000,000/frequency (MHz/MHz), and the molecular weight of 300,000,000 (m)/meter is the propagation speed of the radio wave in the atmosphere (ie, the speed of light), so The wavelength of 15 megahertz (MHz) is, wavelength = 300000000 / 15000000 = 20 (m) / meter. Of course, short-wave broadcasts have many frequency ranges. It's cumbersome to remember these frequencies and relative wavelengths, but it's not a problem if you grab a trick. First remember the relationship between frequency and wavelength, for example, 15 megahertz (MHz) is 20 (m), then double the frequency, the wavelength is halved, the opposite frequency is halved, and the wavelength is doubled. For example, 15MHz is 20 (m), then 30MHz is 10 (m), and 7.5MHz is 40 (m), which is much easier. 

If the above is too complicated, you can also understand it simply: the frequency is used to indicate the exact location of a station; the wavelength is used to indicate the approximate location of the station, and the (m) band is used to indicate a small range of frequencies. 

For example, the 19 (m) band represents the frequency range of 15.10 - 15.60 MHz. (Please refer to the International Broadcasting (m) Band Table below) 

Radio spectrum: Generally, radio waves refer to the vertices from the extremely low frequency of 10 kHz to the very high frequency of 30 GHz (Giga Hertz). Because the radio spectrum outside this range has a very different characteristics, such as light and X-rays. Etc., at the above 10KHz to 30GHz, usually divided into seven regions, see the table below, where the high frequency 3 ~ 30MHz is the short wave we discussed. 

     Division of the radio spectrum: 
     Very low frequency VLF Very Low frequency range 10KHz - 30KHz 
     Low frequency LF (commonly known as long wave LW) Low frequency frequency range 30KHz - 300KHz 
     IF MF (commonly known as medium wave MW) Medium frequency frequency range 30KHz - 3000KHz 
     High frequency HF (commonly known as short wave SW) High frequency frequency range 3MHz - 30MHz 
     Extremely high frequency VHF (commonly known as ultrashort wave, while civil broadcasting in the frequency range of 88-108MHZ is commonly known as FM radio FM) Very High frequency frequency range 30MHz - 300MHz 
     UHF Ultra High Frequency Frequency Range 300MHz - 3000MHz 
     Extremely high frequency SHF Super High frequency range 3000MHz - 30000MHz 

International Shortwave Broadcasting Band: The use of all radio frequencies in the world is allocated by the International Telecommunications Union. The International Telecommunication Union (ITU) is an international telecommunication management organization affiliated with the United Nations. It regularly convene meetings of Member States to determine the allocation and use of radio frequencies. There are 13 international shortwave broadcasting bands developed by the ITU. Each (m) band has a certain frequency range, you may feel strange, from 2.3-26.1MHZ is divided into 13 segments, why not coherent? This is because: in the high-frequency spectrum (3-30MHz), the International Telecommunications Regulatory Organization (ITU) has regulations, in addition to international short-wave broadcasting, there are many other communications purposes. You can easily find the (m) band division table on the radio manual.