Digital television (DTV) is the transmission of television signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative advancement and represented the first significant evolution in television technology since color television in the 1950s. Modern digital television is transmitted in high-definition television (HDTV) with greater resolution than analog TV. It typically uses a widescreen aspect ratio in contrast to the narrower format (4:3) of analog TV. It makes more economical use of scarce radio spectrum space; it can transmit up to seven channels in the same bandwidth as a single analog channel, and provides many new features that analog television cannot. A transition from analog to digital broadcasting began around 2000. Different digital television broadcasting standards have been adopted in different parts of the world; below are the more widely used standards:
Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum, in a one-to-many model. Broadcasting began with AM radio, which came into popular use around 1920 with the spread of vacuum tube radio transmitters and receivers. Before this, most implementations of electronic communication were one-to-one, with the message intended for a single recipient. The term broadcasting evolved from its use as the agricultural method of sowing seeds in a field by casting them broadly about. It was later adopted for describing the widespread distribution of information by printed materials or by telegraph. Examples applying it to "one-to-many" radio transmissions of an individual station to multiple listeners appeared as early as 1898.
Terrestrial television or over-the-air television (OTA) is a type of television broadcasting in which the signal transmission occurs via radio waves from the terrestrial (Earth-based) transmitter of a TV station to a TV receiver having an antenna. The term terrestrial is more common in Europe and Latin America, while in Canada and the United States it is called over-the-air or simply broadcast. This type of TV broadcast is distinguished from newer technologies, such as satellite television, in which the signal is transmitted to the receiver from an overhead satellite; cable television, in which the signal is carried to the receiver through a cable; and Internet Protocol television, in which the signal is received over an Internet stream or on a network utilizing the Internet Protocol. Terrestrial television stations broadcast on television channels with frequencies between about 52 and 600 MHz in the VHF and UHF bands. Since radio waves in these bands travel by line of sight, reception is generally limited by the visual horizon to distances of 64–97 kilometres (40–60 mi), although under better conditions and with tropospheric ducting, signals can sometimes be received hundreds of kilometers distant.
Low-power broadcasting is broadcasting by a broadcast station at a low transmitter power output to a smaller service area than "full power" stations within the same region. It is often distinguished from "micropower broadcasting" and broadcast translators. LPAM, LPFM and LPTV are in various levels of use across the world, varying widely based on the laws and their enforcement.
A non-commercial educational station is a radio station or television station that does not accept on-air advertisements, as defined in the United States by the Federal Communications Commission (FCC) and was originally intended to offer educational programming as part, or whole, of its programming. NCE stations do not pay broadcast license fees for their non-profit uses of the radio spectrum. Stations which are almost always operated as NCE include public broadcasting, community radio, and college radio, as well as many religious broadcasting stations. Nearly all Non-Commercial radio stations derive their support from listener support, grants and endowments, such as the governmental entity Corporation for Public Broadcasting (CPB) that distributes supporting funds provided by the congress to support Public Radio.
Digital terrestrial television is a technology for terrestrial television where television stations broadcast television content in a digital format. DTTV is a major technological advance over analog television, and has largely replaced analog television broadcast, which had been in common use since the middle of the 20th century. Test broadcasts began in 1998 with the changeover to DTTV, also known as the Analog Switchoff (ASO) or Digital Switchover (DSO), which began in 2006 and is now complete in many countries. The advantages of digital terrestrial television are similar to those obtained by digitizing platforms such as cable TV, satellite, and telecommunications: more efficient use of radio spectrum bandwidth, provision of more television channels than analog, better quality images, and potentially lower operating costs for broadcasters.
The All-Channel Receiver Act of 1962 (ACRA), commonly known as the All-Channels Act, was passed by the United States Congress in 1961, to allow the Federal Communications Commission to require that all television set manufacturers must include UHF tuners, so that new UHF-band TV stations could be received by the public. This was a problem at the time since most affiliated stations of the Big Three television networks were well-established on VHF, while many local-only stations on UHF were struggling for survival.
A tuner is a subsystem that receives radio frequency (RF) transmissions, such as FM broadcasting, and converts the selected carrier frequency and its associated bandwidth into a fixed frequency that is suitable for further processing, usually because a lower frequency is used on the output. Broadcast FM/AM transmissions usually feed this intermediate frequency (IF) directly into a demodulator that converts the radio signal into audio-frequency signals that can be fed into an amplifier to drive a loudspeaker.
WOCH-CD, virtual channel 41, was a low-power, Class A Charge!-affiliated television station licensed to Chicago, Illinois, United States. The station was owned by NRJ TV, LLC.
KOZK is a PBS member television station licensed to Springfield, Missouri, United States, owned by Missouri State University. The station's studios are located on the Missouri State University campus on National Avenue in southern Springfield, and its transmitter is located on Highway FF north of Fordland.
Mobile television is television watched on a small handheld or mobile device, typically developed for that purpose. It includes service delivered via mobile phone networks, received free-to-air via terrestrial television stations, or via satellite broadcast. Regular broadcast standards or special mobile TV transmission formats can be used. Additional features include downloading TV programs and podcasts from the Internet and storing programming for later viewing.
A digital television adapter (DTA), commonly known as a converter box or decoder box, is a television tuner that receives a digital television (DTV) transmission, and converts the digital signal into an analog signal that can be received and displayed on an analog television set. Some also have an HDMI output since some TVs with HDMI do not have a digital tuner. The input digital signal may be over-the-air terrestrial television signals received by a television antenna, or signals from a digital cable system. It normally does not refer to satellite TV, which has always required a set-top box either to operate the big satellite dish, or to be the integrated receiver/decoder (IRD) in the case of direct-broadcast satellites (DBS).
A coupon-eligible converter box (CECB) was a digital television adapter that met eligibility specifications for subsidy "coupons" from the United States government. The subsidy program was enacted to provide terrestrial television viewers with an affordable way to continue receiving free digital terrestrial television services after the nation's television service transitioned to digital transmission and analog transmissions ceased. The specification was developed by the National Telecommunications and Information Administration (NTIA), with input from the broadcast and consumer electronics industries as well as public interest groups.
In telecommunications, white spaces refer to radio frequencies allocated to a broadcasting service but not used locally. National and international bodies assign frequencies for specific uses and, in most cases, license the rights to broadcast over these frequencies. This frequency allocation process creates a bandplan which for technical reasons assigns white space between used radio bands or channels to avoid interference. In this case, while the frequencies are unused, they have been specifically assigned for a purpose, such as a guard band. Most commonly however, these white spaces exist naturally between used channels, since assigning nearby transmissions to immediately adjacent channels will cause destructive interference to both.
Digital television in the United States is available via digital terrestrial television (DTT), digital cable, satellite television, and IPTV providers.
The Code of Practices for Television Broadcasters, also known as the Television Code, was a set of ethical standards adopted by the National Association of Broadcasters (NAB) of the United States for television programming from 1952 to 1983. The code was created to self-regulate the industry in hopes of avoiding a proposed government Advisory Board and satisfying parental concerns over violence and other matters. Prior to the Television Code, the 1935 NAB Code of Ethics for radio was applied to television but fewer than half of television stations subscribed to it; when the Television Code was first issued, two-thirds of stations became subscribers.
Analog passthrough is a feature found on some digital-to-analog television converter boxes. Boxes without the analog passthrough feature only allow older, analog-only TVs to view digital TV. Those with analog passthrough allow both digital and analog television to be viewed on older TVs.
The digital transition in the United States was the switchover from analog to exclusively digital broadcasting of terrestrial television programming. According to David Rehr, then president and CEO of the National Association of Broadcasters, this transition represented "the most significant advancement of television technology since color TV was introduced." For full-power TV stations, the transition went into effect on June 12, 2009, with stations ending regular programming on their analog signals no later than 11:59 p.m. local time that day.
The Community Broadcasters Association (CBA) was a trade organization representing low-power broadcasting interests, including LPTV and Class A television stations, in the United States of America. It ceased operations in 2009.
The Short-term Analog Flash and Emergency Readiness Act, or SAFER Act, is a U.S. law that required the Federal Communications Commission (FCC) to allow the continuation of full-power analog TV transmissions in 2009 for an additional 30 days for the purpose of broadcasting public service announcements regarding the DTV transition in the United States and emergency information. It is also commonly known as the "DTV nightlight bill" or "analog nightlight", referring to a small nightlight that is left on after all of the other lights are out. Despite the analog shutoff deadline being extended to June 12, 2009 as part of the DTV Delay Act, stations that signed off before the deadline were still permitted to participate in the SAFER Act.
