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Frequency band is a word related to waves and communications.
In the mechanical wave, the frequency band refers to the sound frequency and wavelength, the human ear's feeling of the sound frequency is from the lowest 20Hz to the highest 20KHz, and the human voice frequency range is concentrated between 80Hz and 12kHz, and people's feelings of the sound in different frequency bands are different.
In the field of communication, the frequency band refers to the frequency range of electromagnetic waves, the unit is Hz, according to the size of the frequency, can be divided into:
Very low frequency (VLF) 3 kHz~30 kHz, corresponding to the wavelength of the electromagnetic wave is very long wave 100 km~10 km.
The low frequency (LF) is 30 kHz ~300 kHz, and the corresponding wavelength of electromagnetic wave is 10 km~1 km.
Intermediate frequency (MF) 300 kHz ~ 3000 kHz, corresponding to the wavelength of electromagnetic wave 1000 m~100 m.
High frequency (HF) 3 MHz ~ 30 MHz, corresponding to the wavelength of the electromagnetic wave is 100 m~10 m.
Very high frequency (VHF) 30 MHz~300 MHz, corresponding to the wavelength of electromagnetic wave 10 m~1 m.
Ultra-high frequency (UHF) 300 MHz ~ 3000 MHz, corresponding to the wavelength of electromagnetic wave 100cm~10 cm decimeter wave.
Ultra-high frequency (SHF) 3 GHz~30 GHz, corresponding to the wavelength of electromagnetic waves 10 cm~1 cm.
Extremely high frequency (EHF) 30 GHz~300 GHz, corresponding to the wavelength of electromagnetic wave 10 mm ~ 1 mm millimeter wave.
To the high frequency 300 GHz ~ 3000 GHz, the wavelength of the corresponding electromagnetic wave is 1 mm ~ 0.1 mm.
- Chinese name
- Frequency band
- Foreign name
- Frequency Band
The frequency band used in wireless communication is only a small part of the electromagnetic frequency band, which defines the frequency range of radio waves.
In order to make rational use of spectrum resources and ensure that various industries and services do not interfere with each other when using spectrum resources, the International Telecommunication Union Wireless Committee (ITU-R) has issued international radio regulations, which have unified frequency range provisions for the wireless frequency bands used by various services and communication systems.
The frequency range of these bands will be slightly different in the actual application of various countries and regions, but they must be within these ranges stipulated internationally.
In accordance with
International radio regulation
According to the provisions, existing radio communications are divided into aviation communications, maritime communications, land communications,
Satellite communication
Radio, television, radio navigation, positioning, telemetry, remote control, space exploration and other more than 50 different services, and a certain frequency band is specified for each service.
Various communication systems also have a selective and reasonable allocation of frequency bands for the use of channels, so as to rationally utilize and save spectrum resources as much as possible to meet the requirements of efficient and reliable transmission.
For wired channels, it is important to select different transmission media and channel frequency multiplexing for broadband media. Generally, according to the channel service requirements, the frequency band is determined by considering the performance characteristics of the aforementioned wired channel (constant parameter) required by each of them, such as loss, delay and phase shift characteristics, as well as the lowest and highest cut frequency.
Submarine communication is suitable for very low frequency band, so it has good transmission performance. Any baseband signal transmission uses the baseband signal bandwidth as the full low frequency band, analog voice low-frequency transmission only uses 300 to 3400Hz or high-quality sound (music) from 50Hz to 15kHz bandwidth.
The more complicated problem is that all kinds of wireless communication should choose and allocate the working frequency band appropriately according to the characteristics of space electromagnetic wave propagation. ITU-R has made specific rules for spectrum allocation, and all departments in each country have scientific and strict control over frequency use.
Electromagnetic waves are generally divided into three ways from transmission to reception: one is called "ground wave"; Second, it is called "space wave" that propagates in a straight line between two points in space; The third is to rely on the ionosphere above the Earth to reflect to the ground in a single or multi-hop mode of propagation, called "sky wave".
Ground waves propagating along the surface will be attenuated by the ground as a non-good conductor due to the induced current generated by the jump propagation of electromagnetic waves along the ground, and the higher the frequency, the greater the skin effect, the greater the loss. Therefore, ground waves are suitable for medium and medium waves (that is, hundreds of KHZ to several megahertz), such as civil broadcasting from 535kHz to 1605kHz frequency band (one program per 10kHz) is an example.
The short wave (high frequency band) of several megahertz to tens of megahertz is suitable for sky wave propagation, and the distance between sending and receiving is much larger than that of ground waves, which can reach hundreds to thousands of kilometers, depending on the size of the antenna incidence Angle. As mentioned above, the ionosphere will absorb and attenuate the reflected electromagnetic waves, and the greater the ionization concentration, the greater the loss, and the fluctuation attenuation of electromagnetic waves caused by random changes in the ionosphere is the fading phenomenon.
If the wavelength is shorter, that is, the higher frequency band, such as hundreds of megahertz to several gigahertz (109MHz) or more, it enters the microwave band. Electromagnetic waves in this band are rarely absorbed by the ionosphere and are no longer reflected back to the ground. Such as satellite communications, electromagnetic waves can travel through the ionosphere to the satellite. This kind of space wave propagation is similar to light, not only in straight line propagation, but also in electromagnetic wave diffraction (diffraction), which can bypass some local obstacles. For example, the microwave relay is transmitted in a straight line between the ground point and the point, in addition to being affected by the ground environment (swamps, mountains, forests, etc.), and the antenna is inconvenient to set up too high, so the relay (relay) section is only 40 or 50 kilometers, usually called "line-of-sight" communication.
Wireless communication requires transceiver antenna length and wavelength λ to match the antenna size of 1/4·λ, so the radio antenna using omnidirectional antenna for civil broadcasting cannot be stably erected more than 100 meters. The GSM mobile phone antenna in the 900MHz band can be as short as a few centimeters long, which brings great convenience for the miniaturization and portability of mobile phones.
All wireless communications are transmitted through free space, in order to make reasonable use of frequency bands, and various communications in various regions do not interfere with each other, ITU scientifically allocates the frequency bands applicable to various communication systems, and each frequency band frequency corresponds to its wavelength and its name
International Telecommunication union
The Wireless Committee (ITU-R) promulgated that each country, region and city has a corresponding radio management committee, which is responsible for the reasonable coordination of wireless frequency points in the country and the region.
The third generation mobile communication System (3G) is IMT-2000, which is the name of the future Public Land Mobile Communication System (FPLMTS) proposed by the International Telecommunication Union (ITU) in 1985. The International Mobile Communication System (IMT-2000) will be commercially available in the 2000MHz band around the year 2000.
In 1992, the World Radio Administration Conference (WARC) allocated 230MHz bandwidth to IMT-2000 based on ITU-R estimates of the traffic volume and spectrum required for IMT-2000. The 1885-2025mhz and 2110-2200mhz bands are available for IMT-2000 services on a global basis; 1980 ~ 2010MHz and 2170 ~ 2200MHz are 60MHz for satellite mobile service bands. The remaining 170MHz is the land mobile service frequency band, in which the symmetric frequency band is 2 × 60MHz and the asymmetric frequency band is 50MHz.
After the issuance of 3G licenses, the relevant state departments have issued 3G frequency bands to the three major operators, of which TD-SCDMA has obtained a total of 35M frequency band spectrum resources, while WCDMA and CDMA have obtained 30M frequency band, which shows that the country is still tilted in spectrum resources to TD-SCDMA.
For example, GSM has two bands: the 900 MHz band and the 1800 MHz band. Among them, the transmission and reception frequency ranges of China's GSM900 MHz band are:
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China Mobile: 935 MHz~954 MHz, 890 MHz~909 MHz;
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China Unicom: 954 MHz~960 MHz, 909 MHz~915 MHz.
The transmitting and receiving frequency ranges of China's GSM1800 MHz band are:
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China Mobile: 1805 MHz~1815 MHz, 1710 MHz~1720 MHz;
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China Unicom: 1840 MHz~1850 MHz, 1745 MHz~1755 MHz.
Taking 4G standard LTE as an example, LTE has a very large number of frequency bands, LTE FDD has a total of 22 frequency bands, labeled 1~22, in which the frequency range is not defined except the frequency band labeled 15 and 16 as the reserved frequency band, and the other frequency bands have a frequency range. LTE TDD has a total of 9 bands, labeled 33~41, in China, LTE is currently divided into four bands: Band A, band D, band E and band F, their frequency range is 2010 MHz~ 2025 MHz, 2570 MHz~2620 MHz, 2320 MHz~ 2370 MHz (2300 MHz~ 2400 MHz), 1880 MHz~ 1920 MHz, respectively. Corresponding to the international label 34, 38, 40 and 39 frequency bands.
1. 20Hz- 60Hz part. This lift gives the music a powerful feeling, a very loud feeling, like thunder. If the elevation is too high, it will bang the head, deafening, resulting in poor hearing, especially the low frequency response is poor and the low frequency is too much sound equipment.
2. 60Hz- 250Hz part. This is the low-frequency structure of the music, which contains the basic notes of the rhythm section, including the base note and the tonic note of the rhythm note. Its proportion to the high tone constitutes the balanced property of the timbre structure. Lifting this segment will plump the sound, over-lifting will produce a rumble, and attenuating this band and the high segment will make the sound thin.
3. 250Hz--4KHz part. This section contains the low-frequency harmonics of most Musical Instruments, which also affects the reduction of voices and Musical Instruments, and should be adjusted to match the setting of the front bass, otherwise the sound quality will become very poor. If raised too much it will sound like a telephone; For example, excessive elevation of 400Hz and 600Hz will make the sound like the sound of a car horn; If the 3KHz is raised too much, it will mask the identification sound of speech, that is, the speech is unclear, and the lip sound "m, b, v" is difficult to distinguish; If the 1kHz and 3kHz are raised too much, the sound will have a cold feeling.
4. 4kHz--5KHz part. This is the frequency band that affects air inspiration. Raising this frequency band makes people feel ethereal, the distance between the sound source and the listener appears to be slightly farther away, and the attenuation will make the sense of distance of the sound closer.
5. 6kHz- 16kHz part. This band controls the coolness, detail and air of the tone. Generally speaking, lifting this part makes the sound cool and ethereal, but it can also cause excessive dental sound; This part of the attenuation makes the sound warm, but the sound quality is slightly not delicate. This frequency band is suitable for restoring human voice.
POP: Pop music, it requires both vocal and instrumental music, the combination is relatively average, so the EQ curve is not very volatile.
ROCK: Rock music, its high and low ends are greatly enhanced, the bass makes the music powerful, the rhythm is very strong, and the low frequency part is powerful and even jarring.
JAZZ: Compared with POP, it raises the part of 250~750Hz to enhance the sense of presence.
Classical: Classical music, which promotes both the high and low parts, mainly highlighting the performance of the instrument.
The frequency range of the sound emitted by the human throat is relatively narrow, mainly concentrated in the mid-frequency part.
Everyone feels different for different frequencies of sound, the frequency response of audio playback equipment is different, and the listening curve of people is only drawn according to statistical data, so the sound that sounds natural to others may feel uncomfortable, and the adjustment of the equalizer needs to be personalized according to their own listening characteristics and the playback equipment used.
