Frequency modulation, amplitude modulation, short wave, long wave
What is FM (FM), amplitude modulation (AM), short wave (SW), long wave (LW)?
There are AM and FM bands on general radios or cassette recorders. I believe you are all familiar with these bands. These two bands are used for listening to domestic radio. If there is a SW band on the radio, then in addition to the domestic shortwave radio, You can also listen to radio programs from all over the world. To give you a better understanding of radio usage, here's a simple explanation of what AM,FM,SW,LW is.
In fact, AM and FM refer to two different modulation modes in wireless electricity:. AM: Amplitude Modulation is called amplitude modulation, and FM: Frequency Modulation is called frequency modulation. Only in general the medium wave broadcast (MW: Medium Wave) uses the amplitude modulation (AM) method, unconsciously, the MW and the AM draw the equal sign. In fact, MW is just a lot of broadcasts using AM modulation, such as the modulation mode used in international short-wave broadcasting in high frequency (3-30MHz) is also A M, even 116-136MHz, which has a higher frequency than FM broadcasting, uses AM, but what we call the AM band is the medium wave broadcast (MW).
What about FM? It is similar to the fate of MW. We are used to using FM to refer to general FM broadcasting (76-108MHz, 87.5-108MHz in China, 76-90MHz in Japan). In fact, FM is also a modulation, even in the short wave range between 27-30MHz, as an amateur radio station, in space. Artificial satellite communication applications of the band, also using FM (FM) mode.
And SW? In fact, can be said to be a simple term for short-wave, the correct saying should be high-frequency (HF:High Frequency) more appropriate. And how did the name shortwave come from? In terms of wavelength, the medium wave (MW) is between 200 and 600 meters (meters), while the HF wavelength is between 10 and 100 meters, so compared with the above wavelength, the HF wavelength is indeed shorter. So HF is called shortwave (SW: Short Wave).
Similarly, this section of the spectrum between 150KHz-284KHz, which has a lower frequency than the medium-wave MW, is used for broadcasting, and at wavelengths it is about 1,000 to 2,000 metres (meters), which is obviously "longer" than the 200-600 meters of MW. So the broadcast of this spectrum is called a long wave (LW: Long Wave). In fact, both medium wave (MW) and short wave (SW) of long wave (LW), are modulated by AM.
For the general receiver, the FM,MW,LW band is for you to listen to the domestic radio, but at present there is no LW radio station in our country, and the SW band is mainly for you to listen to the domestic / international long distance broadcasting.