How do you define short wave, medium wave and long wave? What's the difference between FM and AM? What do they mean?

Short wave refers to radio waves with a frequency of 3 ~ 30 MHz. Short wave is short, the diffraction ability of ground wave propagating along the surface is poor and the effective propagation distance is short. When the short wave propagates in the form of sky wave, it is hardly absorbed in the ionosphere, which is beneficial to the reflection of the ionosphere. The jumping distance of 100 ~ 4000 km can be obtained after one reflection. After several consecutive reflections from the ionosphere and the earth, it will spread further. The frequency range of short wave (SW) in China's radio broadcasting is 2 ~ 24 MHz, and some radio stations divide the short wave frequency band into short wave 1(SW 1) and short wave 2(SW2).

Medium wave (MW: medium wave) adopts the method of amplitude modulation, and unconsciously, medium wave and medium wave are equated. In fact, microwave is just a kind of broadcast using amplitude modulation. For example, the modulation mode used in international short-wave broadcasting at high frequency (3-30MHz) is AM, even the aviation navigation communication with higher frequency than FM broadcasting (116-136 MHz) is AM, but what we call AM band everyday refers to medium-wave broadcasting (M).

English name of long wave: Long Wave. Long wave (including ultra-long wave) in electronics refers to radio wave with frequency below 300kHz and wavelength of 1000 ~ 10000. The long wave in meteorology refers to the fluctuation with the wavelength of 3000 ~ 8000 km in the atmospheric circulation of the westerlies in the upper and middle troposphere. Because the ionosphere in the atmosphere has a strong absorption effect on long waves, long waves mainly propagate along the earth's surface, with low propagation loss and strong diffraction ability. Ultra-long waves with frequencies below 30kHz can spread all over the world. When long wave propagates, it has the advantages of stable propagation and little influence by nuclear explosion and atmospheric disturbance. Spreading in seawater and soil, the absorption loss is also very small.

For the difference between FM and am, AM abbreviation = AM; AM (broadcast); High and low signal variability is expressed as a percentage (%). Fm abbreviation = Fequecy modulation frequency modulation; Frequency modulation (broadcasting); The modulation degree of signal frequency is expressed in (khz or mhz). Early technology was not developed. In the vacuum tube era, amplitude modulation is used, the receiving circuit is simple and the radio transmission frequency is low. Only in the transistor era below 1620khz, the electromechanical circuit of FM receiver is complex, the radio transmission frequency is high, and the sn characteristics and crosstalk characteristics are better than am.

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Specific:

Generally, there are AM and FM bands on radios or tape recorders, which I believe you are familiar with. These two bands are for you to listen to domestic broadcasts. If there is SW band on the radio, you can listen to radio programs from all over the world in addition to domestic short-wave radio stations. In order to make you better understand the use of radio, let's briefly explain what am, FM, short wave and long wave are.

In fact, AM and FM refer to two different modulation methods in radio science. AM: AM is called AM, FM: FM is called FM. It's just that the general medium wave (MW: MW) adopts the method of amplitude modulation (AM), and unconsciously, an equal sign is drawn between MW and AM. In fact, microwave is just a kind of broadcast using amplitude modulation. For example, the modulation mode used in international short-wave broadcasting at high frequency (3-30MHz) is AM, and even aviation navigation communication with higher frequency than FM broadcasting (116-136 MHz) uses AM, but the AM band we refer to in daily life refers to medium-wave broadcasting (MW).

What about FM? This is also similar to the fate of MW. We are used to referring to general FM broadcasting (76- 108MHz in China, 87.5- 108MHz in Japan and 76-90MHz in Japan). In fact, FM is also a modulation method. Even in the short wave range of 27-30 MHz, it is also used as the band of amateur radio, space and satellite communication.

And SW? In fact, it can be said to be a simple name for short wave, and the correct term should be HF (high frequency). How did the name shortwave come from? In terms of wavelength, the medium wave (MW) is between 200 and 600 meters, while the wavelength of HF is between 10 and 100 meters. Compared with the above wavelength, the wavelength of HF is indeed shorter, so HF is called short wave (SW).

Similarly, the frequency spectrum between 150 kHz and 284 kHz below MW is also used for broadcasting. As far as wavelength is concerned, it is about 1000 ~ 2000 meters (meters), which is obviously much longer than MW's 200-600 meters. Therefore, the broadcasting of this spectrum is called long wave. In fact, whether long wave (LW), medium wave (MW) or short wave (SW) are modulated by AM.

For ordinary radios (tape recorders), FM, MW and LW bands are used for you to listen to domestic broadcasts, but there is no LW radio station in China at present, and SW band is mainly used for you to listen to domestic/international long-distance broadcasts.

O(∩_∩)o is a bit long and thin, I hope I can help you-