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C band

The C band is a name given to certain portions of the electromagnetic spectrum, including wavelengths of microwaves that are used for long-distance radio telecommunications. The IEEE C-band (4 GHz to 8 GHz) - and its slight variations - contains frequency ranges that are used for many satellite communications transmissions, some Wi-Fi devices, some cordless telephones, and some weather radar systems. For satellite communications, the microwave frequencies of the C-band perform better under adverse weather conditions in comparison with Ku band (11.2 GHz to 14.5 GHz) microwave frequencies, which are used by another large set of communication satellites.[1] The adverse weather conditions, collectively referred to as rain fade, all have to do with moisture in the air, including rain and snow.

Contents


The NATO C-band

The NATO C-band is that portion of the radio spectrum between 500 megahertz (MHz) and 1000 MHz, but this terminology is rarely used in the NATO members that are located in North America.

The IEEE C-band

C-band antennas of this type became widespread in the United States in the 1950s The IEEE C-band is a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 4.0 to 8.0 gigahertz (GHz),[2] but this definition is the one that is followed by radar manufacturers and users, but not necessarily by microwave radio telecommunications users.

The communications C-band was the first frequency band that was allocated for commercial telecommunications via satellites. The same frequencies were already in use for terrestrial microwave radio relay chains. Nearly all C-band communication satellites use the band of frequencies from 3.7 to 4.2 GHz for their downlinks, and the band of frequencies from 5.925 GHz to 6.425 GHz for their uplinks. Note that by using the band from 3.7 to 4.0 GHz, this C-band overlaps somewhat into the IEEE S-band for radars.

The C-band communication satellites typically have 24 radio transponders spaced 20 MHz apart, but with the adjacent transponders on opposite polarizations. http://www.lyngsat.com/america.html Hence, the transponders on the same polarization are always 40 MHz apart. Of this 40 MHz, each transponder utilizes about 36 MHz. (The unused 4.0 MHz between the pairs of transponders acts as "guard bands" for the likely case of imperfections in the microwave electronics.)

The C-band is primarily used for open satellite communications, whether for full-time satellite TV networks or raw satellite feeds, although subscription programming also exists. This use contrasts with direct broadcast satellite, which is a completely closed system used to deliver subscription programming to small satellite dishes that are connected with proprietary receiving equipment.

The satellite communications portion of the C-band is highly associated with television receive-only satellite reception systems, commonly called "big dish" systems, since small receiving antennas are not optimal for C-band systems. Typical antenna sizes on C-band capable systems ranges from 7.5 to 12 feet (2.5 to 3.5 meters) on consumer satellite dishes, although larger ones also can be used.

The C-band frequencies of 5.4 GHz band [5.15 to 5.35 GHz, or 5.47 to 5.725 GHz, or 5.725 to 5.875 GHz, depending on the region of the world] is used for IEEE 802.11a Wi-Fi and cordless telephone applications, leading to occasional interference with some weather radars that are also allocated to the C-band.

C-band variations

Slight variations in the assignments of C-band frequencies have been approved for use in various parts of the world, depending on their locations in the three International Telecommunications Union radio regions. Note that one region includes all of the Americas; a second includes all of Europe and Africa, plus all of Russia, and the third region includes all of Asia outside of Russia, plus Australia and New Zealand. This latter region is the most populous one, since it includes the People's Republic of China, India, Pakistan, Japan, and Southeast Asia.

C-Band Variations Around The World
Band Transmit Frequency
(GHz)
Receive Frequency
(GHz)
Standard C-Band 5.850 6.425 3.625 4.200
Extended C-Band 6.425 6.725 3.400 3.625
INSAT / Super-Extended C-Band 6.725 7.025 4.500 4.800
Russian C-Band 5.975 6.475 3.650 4.150
LMI C-Band 5.7250 6.025 3.700 4.000

Amateur radio

The Radio Regulations of the International Telecommunication Union allow amateur radio operations in the frequency range 5.650 to 5.925 GHz, and amateur satellite operations are allowed in the ranges 5.830 to 5.850 GHz for down-links and 5.650 to 5.670 GHz for up-links. This is known as the 5-centimeter band by amateurs and the C-band by AMSAT.

Other microwave bands

The microwave spectrum is usually defined as the electromagnetic spectrum that ranges from 1.0 GHz to 30 GHz in frequency, but some antiquated usages includes lower frequencies. Most common applications are within the 1.0 to 30 GHz range. Microwave frequency bands, as defined by the Radio Society of Great Britain (RSGB), are shown in the table below. Note that frequencies above 30 GHz are typically said to be in the "millimeter wave". because their wavelengths can be conveniently measured in millimeters (mm). The frequency of 30 GHz corresponds quite closely to a wavelength of 10 mm, or 1.0 centimeter.

L band 1 to 2 GHz
S band 2 to 4 GHz
C band 4 to 8 GHz
X band 8 to 12 GHz
Ku band 12 to 18 GHz
K band 18 to 26.5 GHz
Ka band 26.5 to 40 GHz
Q band 30 to 50 GHz
U band 40 to 60 GHz
V band 50 to 75 GHz
E band 60 to 90 GHz
W band 75 to 110 GHz
F band 90 to 140 GHz
D band 110 to 170 GHz

Footnote: "P-band" is sometimes incorrectly used for the Ku-band. "P" for "previous" was a radar band used in the United Kingdom that ranged from 250 to 500 MHz, which is now completely obsolete by the IEEE Standard 521, see http://www.radioing.com/eengineer/bands.html and http://www.microwaves101.com/encyclopedia/letterbands.cfm. For other definitions see Letter Designations of Microwave Bands

Fiber optic communications

In infrared optical communications, C-band refers to the wavelength range 1530 1565 nm, which corresponds to the amplification range of erbium doped fiber amplifiers (EDFAs).[3]

See also

  • Big ugly dish
  • Communications satellite
  • Satellite dish
  • Television receive-only
  • 4DTV

Notes

External links

ca:Banda C es:Banda C eu:C banda fa: fr:Bande C pl:Pasmo C pt:Banda C ru:C- vi:B ng t n C zh:C






Source: Wikipedia | The above article is available under the GNU FDL. | Edit this article



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