C band
C band ("compromise" band) is a portion of electromagnetic spectrum in the microwave range of frequencies ranging from 4 to 6 GHz. (For military use, by NATO designation, "C band" is the frequency range between 0.5 and 1 GHz.)
C band is primarily used for satellite communications, normally downlink 3.7 – 4.2 GHz, uplink 5.9 – 6.4 GHz, usually via 24 36-MHz transponders on board a satellite. Most C band satellites use linear polarization, while a handful (particularly older Intelsat satellites) use circular polarization.
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 middle 1990's , the number of homes using C band satellite systems in the United States for general reception has vastly declined 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 in Europe, where the Ku band has traditionally dominated. In many parts of the world, C band is often used to cover a very broad area, for example all of Africa or China. 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.
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 highly associated with TVRO satellite reception systems or "big dish" systems. Larger antennas and more expensive receivers, C band usually provides better video quality and is less affected by rain attenuation than the Ku band.
Military designation
The NATO C band is defined as frequency band between 0.5 and 1 GHz (0.3 and 0.6 m).
