C band
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| NATO Radio bands |
| IEEE Radio bands |
C band is the label for three portions of the electromagnetic spectrum used in different ways. It is important to note the differences described in the rest of the article.
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[edit] NATO C band
NATO C band is defined as frequency band between 0.5 and 1 GHz (0.3 and 0.6 m). NATO C band is used in many countries' weather radar systems.
[edit] IEEE C band
IEEE C band ("compromise" band) is a portion of the electromagnetic spectrum in the microwave range of frequencies, ranging from 4 to 8 GHz. It is an electronic and electrical standard defined by the IEEE.
It is primarily used for satellite communications, normally downlink 3.7 – 4.2 GHz, (LOF 5.150 GHz, uplink 5.9 – 6.4 GHz), usually via twenty-four 36 MHz-wide transponders on board a satellite. Most C band satellites serving North America use linear polarization, while most of those serving other continents (particularly Intelsat satellites) use circular polarization since ionospheric Faraday Rotation affects C band frequencies, particularly in the tropics. The 802.11a wireless networking standard operates in the 5 GHz area, and some recent-model cordless telephones use frequencies in the 5.8 GHz vicinity.
The applications include full-time satellite TV networks or raw satellite feeds, although subscription programming also exists. There are over thirty C band satellites in Geosynchronous orbit serving North America, which provide more than 1,000 video channels and countless audio services. In the past, direct C band reception was the only satellite television option available to consumers. Since the introduction of high-powered direct broadcast satellite systems, which normally used small 18-inch (45-cm) stationary dishes (in contrast to the large dishes and motors required by C band systems) in the mid-1990s, the number of homes using C band satellite systems in the United States for general reception has declined precipitously while small-dish systems enjoyed unprecedented success. Despite this, C band satellites continue to be a key important distribution method for cable networks in the United States (to cable head-ends and mini-dish DBS services) and other network/broadcast users. For example, most satellite-distributed syndicated and network television shows are pre-aired for affiliate and Canadian pick-up by C band. Radio stations picking up satellite-fed programming also constitute an important American user of C band, with a major American radio "neighborhood" located on the AMC 8 satellite at the 139°W orbital position.
C band came into domination in the 1970s with the launch of Canada's Anik satellites, and Western Union's Westar and RCA's Satcom satellites.
Beginning in 1984, the major networks transitioned to full-time satellite delivery for television programs. ABC established a satellite home on the Telstar 301 satellite and later Telstar 302, and CBS launched two transponders on GTE's Comstar D4, later transitioning to Telstar 301 and Telstar 302. NBC maintained a C band feed for the east coast on RCA's Satcom 1R as part of its Skypath affiliate feed service for many years, but opted for Ku band delivery of West coast programming, and other affiliate feeds.
Typical antenna sizes on C band capable systems for home reception in North America range from 7.5 to 12 feet (2 to 3.5 m). In other regions of the world, such as Europe and parts of Asia, considerably smaller dishes can be used due to high-powered satellites in this band and more distance between satellites in the orbital arc (as opposed to the two-degree spacing common over North America).
C band usage is less common within Europe, where the Ku band has traditionally dominated. C band has been used for international communications between countries and for this purpose the satellite coverage beams have been made very large, typically covering many countries within a particular hemisphere or zone, for example all of Europe and Africa or Chinaand south east Asia. Indeed, many C band satellites have global beams with gigantic coverage areas. For example, the global beam of the Thaicom 3 satellite, positioned at the 78.5°E orbital slot (over the Indian Ocean) has a coverage range extending over most of Europe, Asia, Africa, and Australia. Similarly, a satellite over the Atlantic Ocean Region provides coverage, and interconnection, for North and South America plus Europe and Africa.
C band direct-to-home reception contrasts with the newer and now more common direct broadcast satellite, which is a completely closed system used to deliver subscription programming to small satellite dishes connected to proprietary receiving equipment.
C band is associated with both television receive-only (TVRO) satellite reception systems and "big dish" systems. Big, expensive, dish systems are used where the number of earth station sites is small and the objective is to reduce the satellite power used, and thus cost, per phone call to a minimum. Small ground antennas are inefficient since they need much more power from the satellite (inversely to their area) but small dishes are very appropriate in large networks where the aggregate total cost of very many dishes is the dominant factor.
C band is much less affected by rain attenuation than the Ku band and C band is therefore preferred for telecommunications services in heavy rainfall areas.
[edit] Optical communications C band
The C band in optical communications refers to near infrared wavelengths ranging from about 1525 nm to 1565 nm.
| The Electromagnetic Spectrum (Sorted by wavelength, short to long) |
|
| Gamma ray | X-ray | Ultraviolet | Visible spectrum | Infrared | Terahertz radiation | Microwave | Radio waves | |
| Visible (optical) spectrum: | Violet | Blue | Green | Yellow | Orange | Red |
|---|---|
| Microwave spectrum: | W band | V band | K band: Ka band, Ku band | X band | C band | S band | L band |
| Radio spectrum: | EHF | SHF | UHF | VHF | HF | MF | LF | VLF | ULF | SLF | ELF |
| Wavelength designations: | Microwave | Shortwave | Mediumwave | Longwave |
