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Sign-off (or closedown) is the sequence of operations involved when a radio or television station shuts down its transmitters and goes off the air for a predetermined period; generally this occurs during the overnight hours. It is the opposite to a sign-on (or startup), which usually takes place at the start of the day. ==Overview== Sign-offs, like sign-ons, vary from country to country, from station to station, and from time to time; however, most follow a similar general pattern. Many stations follow the reverse process to their sign-on sequence at the start of the day. Sign-off messages can be initiated by a broadcast automation system just as for other television programming, and automatic transmission systems can cut off the carrier signal and trigger the actual shutdown of the transmitter by remote control. Generally, after the carrier signal is cut, the viewer only sees or hears static after an analog television station signs off. Digital stations will likely display a message after the sign off; however, they may simply cut to a black screen with no sound. Occasionally, the signal is cut off entirely, causing digital broadcast receivers (cable/satellite boxes, digital TVs/converter boxes) to display error messages. Both sign-offs and sign-ons have become less common with the increasing prevalence of twenty-four hours a day, seven days a week broadcasting. They are, however, still conducted by a number of stations around the world, often by stations catering to small-markets or those in less developed countries, or when stations need to shut down for transmitter maintenance. Another consideration for whether providers shutdown is power consumption; aerial signals, such as those for UHF analog TV transmissions, can require tens of thousands of watts of power, making electricity a major expense, while power consumption would usually be considerably lower for cable and satellite providers. In relation to costs, viewer numbers are also a consideration. Another consideration is the licence issued by the government which indicates when their transmitters can be operated. For broadcasters that do still close for a period each day, the station close most often takes place overnight or during the early hours of the morning. The daily sign-off typically occurs between around 11:00 p.m. and 2:00 a.m. and the station will remain closed until about 5:00 a.m. to 7:00 a.m., although in countries with limited broadcast coverage, sign-off may occur at earlier times, and sign-on later. Sign-off may also vary depending on the day of the week; for example some broadcasters may run for 24 hours on Saturday nights, but sign-off and close during the week when there are lower viewer numbers. Seasonality is also a consideration where some stations/networks stay open for 24 hours, while rarely few go off the air completely during peak times of religious observances. Many stations, while no longer conducting a sign-off and being off air for a period of time each day, instead run low cost programming during those times of low viewer numbers. This may include infomercials, movies, television shows, simple weather forecasts, low cost news or infotainment programming from other suppliers, or feeds of local cable TV companies' programming via a fiber optic line to the cable headend. Other broadcasters that are part of a radio or television network may run an unedited feed of the network's overnight programming from a central location, without local advertising. Some stations, after doing a sign-off, nonetheless continue to transmit throughout the off-air period on cable/satellite; this transmission may involve a test pattern or static image that is accompanied by music or a local weather radio service. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sign-off」の詳細全文を読む スポンサード リンク
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