Digital television in the United States
In the United States, digital television broadcasts, or DTV, can be received via cable, via internet, via satellite, or via digital terrestrial television — much like analog television broadcasts have been. Full-power analog television broadcasts, however, were required by U.S. federal law to cease by June 12, 2009. Low-power, Class A, and TV Translator stations are not currently required to cease analog broadcasts. Also by law, digital broadcasts — when transmitted as over-the-air signals — must conform to ATSC standards. it is unclear whether satellite operators are free to use their own proprietary standards; and many standards exist for Internet television (most are proprietary).
The U.S. opted to adhere to ATSC standards for broadcast digital television. These standards define, among other things, format and transmission criteria that ensure consistency, accessibility, and fairness for consumers and equipment manufacturers alike in the U.S., as well as international compatibility.
The five main ATSC formats of DTV currently broadcast in the U.S. are:
- Standard definition—480i, to maintain compatibility with existing NTSC sets when a digital television broadcast is converted back to an analog one—either by a converter box or a cable/satellite operator's proprietary equipment
- Enhanced definition—480p, about the same quality as DVDs
- High definition—720p
- High definition—1080i
- High definition—1080p (only used by a few cable operators, currently no terrestrial stations broadcast in 1080p)
Most digital television sets sold in the U.S. use a display with a 16:9 aspect ratio to optimally display HDTV-formatted content. Lower-resolution sources like regular DVDs may be upscaled to the native resolution of the TV.
Most Americans get digital television broadcasts via cable or satellite. Digital cable television systems with an active channel capacity of 750 MHz or greater, are required by the FCC to follow ANSI/SCTE transmission standards with the exception of cable systems that only pass through 8 VSB modulated signals. Digital television sets (equipped with ATSC tuners) are often capable of viewing a baseline set of unencrypted digital programming, known as basic cable or low-tier channels, which typically include local network television affiliates. According to FCC regulations, the remaining encrypted channels must be viewable with a receiver equipped with a CableCARD.
Digital television transmissions over-the-air (OTA) are available in metropolitan areas in the U.S., often carrying both standard-definition and high-definition (HDTV) transmissions of the same stations. As of the analog shut-off date of June 12, 2009, all full power OTA stations in the U.S. by law either transmitted their broadcasts digitally, or shut down.
Many stations used the switch to digital transmission as an opportunity to transition from 480i broadcasts to digital HD OTA broadcasts (either in 720p or 1080i), though this change is voluntary.
Within a distance of 35 to 40 miles from the broadcast stations, it is possible that a simple antenna (such as "rabbit ears") may be adequate to receive a DTV broadcast signal OTA—at least some of the time for some of the channels. Any television equipped with an ATSC tuner may display DTV broadcasts properly. Some customers discovered that terrain, trees, rain, snow, wind, and movement of people around the room interfere with reception to one degree or another, from signals breaking up to total loss of signal. (Few modern ATSC-equipped televisions or converter boxes have internal antennas, in contrast to analog sets available in years past).
Broadcast TV signals in the United States are horizontally polarized.
Transition from analog to digital terrestrial broadcasts in 2009
It was estimated that as of April 2007, 28% of American households had an HDTV set, a total of 35 million sets, and that 86% of owners were highly satisfied with the HDTV programming All TV stations currently broadcast in both digital and analog and major networks broadcast in HD in most markets.
While many in the industry wanted a flexible or delayed deadline, the FCC forced the issue at the behest of Congress. Congress wanted to reclaim some of the spectrum used for analog and repurpose that for emergency services. They also wanted to auction off bandwidth between 76-88 MHz frequencies (channels 5 and 6) and old analog UHF channels 60 to 69, and channels 52 to 59 by mandating DTV tuners be phased into all new TV sets. Many transition dates were proposed, but Congress finally fixed February 17, 2009 (later extending it until June 12, 2009), in law as the maximum end date for analog television authorizations. Because this date comes after the NCAA's Bowl Championship Series and the NFL's Super Bowl XLIII, there will be less of a chance of an acute hardware shortage from people waiting until the last minute to purchase an ATSC tuner than there would have been with a January 1 cutoff.
In March 2008, the FCC requested public comment on turning over the bandwidth occupied by analog television channels 5 and 6 (76–88 MHz) to extend the FM broadcast band when the digital television transition was to be completed in February 2009 (ultimately delayed to June 2009). This proposed allocation would effectively assign frequencies corresponding to the existing Japanese FM radio service (which begins at 76 MHz) for use as an extension to the existing North American FM broadcast band.
Ultimately, VHF Channels 5 and 6 were retained for digital broadcast television use after the transition, though the FCC had continued researching the possibility of re-allocating the two channels to an expanded FM band.
On August 22, 2011, the United States' Federal Communications Commission announced a freeze on all future applications for broadcast stations requesting to use channel 51, to prevent adjacent-channel interference to the A-Block of the 700 MHz band. On December 16, 2011, Industry Canada and the CRTC followed suit in placing a moratorium on any future Channel 51 television station applications.
Early rollout of transition
On May 8, 2008, FCC Chairman Kevin J. Martin announced the agency would test run the transition to digital terrestrial television in Wilmington, North Carolina, beginning September 8, 2008. This test run was to work out problems that might have occurred before the complete transition.
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- 47 U.S.C. § 309(j)(14)(A) as amended by section 3002 of Pub.L. 109–171, S. 1932, 120 Stat. 21, enacted February 8, 2006 S. 1932
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Certain commenters have urged the Commission to give a "hard look" to a proposal that the Commission re-allocate TV Channels 5 and 6 for FM broadcasting73 FR 28400, 28403
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- "The Digital TV Transition: What You Need to Know About DTV" (FCC)
- DTV Transition (DTV Transition Coalition)
- AntennaWeb (local availability of OTA DTV broadcasts, including HD)