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Interested in our radio transmitters? Check out our high and medium power radio transmitters. More information. Request information Do you have questions or need additional information? Get Information. A broadcaster may opt to use a standard-definition SDTV digital signal instead of an HDTV signal, because current convention allows the bandwidth of a DTV channel or " multiplex " to be subdivided into multiple digital subchannels , similar to what most FM radio stations offer with HD Radio , providing multiple feeds of entirely different television programming on the same channel.
This ability to provide either a single HDTV feed or multiple lower-resolution feeds is often referred to as distributing one's " bit budget " or multicasting. This can sometimes be arranged automatically, using a statistical multiplexer or "stat-mux". With some implementations, image resolution may be less directly limited by bandwidth; for example in DVB-T , broadcasters can choose from several different modulation schemes, giving them the option to reduce the transmission bit rate and make reception easier for more distant or mobile viewers.
There are several different ways to receive digital television. One of the oldest means of receiving DTV and TV in general is from terrestrial transmitters using an antenna known as an aerial in some countries. This way is known as Digital terrestrial television DTT. With DTT, viewers are limited to channels that have a terrestrial transmitter in range of their antenna. Other ways have been devised to receive digital television. Among the most familiar to people are digital cable and digital satellite. Finally, an alternative way is to receive digital TV signals via the open Internet Internet television , whether from a central streaming service or a P2P peer-to-peer system.
Some signals carry encryption and specify use conditions such as "may not be recorded" or "may not be viewed on displays larger than 1 m in diagonal measure" backed up with the force of law under the World Intellectual Property Organization Copyright Treaty WIPO Copyright Treaty and national legislation implementing it, such as the U. Digital Millennium Copyright Act. Digital television signals must not interfere with each other, and they must also coexist with analog television until it is phased out.
The following table gives allowable signal-to-noise and signal-to-interference ratios for various interference scenarios. This table is a crucial regulatory tool for controlling the placement and power levels of stations. Digital TV is more tolerant of interference than analog TV, and this is the reason a smaller range of channels can carry an all-digital set of television stations. People can interact with a DTV system in various ways. One can, for example, browse the electronic program guide. Modern DTV systems sometimes use a return path providing feedback from the end user to the broadcaster.
This is possible with a coaxial or fiber optic cable, a dialup modem, or Internet connection but is not possible with a standard antenna. Some of these systems support video on demand using a communication channel localized to a neighborhood rather than a city terrestrial or an even larger area satellite. Each channel is further divided into 13 segments.
The 12 segments of them are allocated for HDTV and remaining segment, the 13th, is used for narrow-band receivers such as mobile television or cell phone. DTV has several advantages over analog TV, the most significant being that digital channels take up less bandwidth, and the bandwidth needs are continuously variable, at a corresponding reduction in image quality depending on the level of compression as well as the resolution of the transmitted image. This means that digital broadcasters can provide more digital channels in the same space, provide high-definition television service, or provide other non-television services such as multimedia or interactivity.
DTV also permits special services such as multiplexing more than one program on the same channel , electronic program guides and additional languages spoken or subtitled. The sale of non-television services may provide an additional revenue source. Digital and analog signals react to interference differently. For example, common problems with analog television include ghosting of images, noise from weak signals, and many other potential problems which degrade the quality of the image and sound, although the program material may still be watchable.
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With digital television, the audio and video must be synchronized digitally, so reception of the digital signal must be very nearly complete; otherwise, neither audio nor video will be usable. Short of this complete failure, "blocky" video is seen when the digital signal experiences interference. Analog TV began with monophonic sound, and later developed multichannel television sound with two independent audio signal channels. DTV allows up to 5 audio signal channels plus a sub-woofer bass channel, with broadcasts similar in quality to movie theaters and DVDs.
DTV images have some picture defects that are not present on analog television or motion picture cinema, because of present-day limitations of bit rate and compression algorithms such as MPEG This defect is sometimes referred to as " mosquito noise ". Because of the way the human visual system works, defects in an image that are localized to particular features of the image or that come and go are more perceptible than defects that are uniform and constant. However, the DTV system is designed to take advantage of other limitations of the human visual system to help mask these flaws, e.
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Broadcast, cable, satellite, and Internet DTV operators control the picture quality of television signal encodes using sophisticated, neuroscience-based algorithms, such as the structural similarity SSIM video quality measurement tool, which was accorded each of its inventors a Primetime Emmy because of its global use.
Changes in signal reception from factors such as degrading antenna connections or changing weather conditions may gradually reduce the quality of analog TV.
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The nature of digital TV results in a perfectly decodable video initially, until the receiving equipment starts picking up interference that overpowers the desired signal or if the signal is too weak to decode. Some equipment will show a garbled picture with significant damage, while other devices may go directly from perfectly decodable video to no video at all or lock up. This phenomenon is known as the digital cliff effect. Block error may occur when transmission is done with compressed images.
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A block error in a single frame often results in black boxes in several subsequent frames, making viewing difficult. For remote locations, distant channels that, as analog signals, were previously usable in a snowy and degraded state may, as digital signals, be perfectly decodable or may become completely unavailable. The use of higher frequencies will add to these problems, especially in cases where a clear line-of-sight from the receiving antenna to the transmitter is not available. Television sets with only analog tuners cannot decode digital transmissions.
When analog broadcasting over the air ceases, users of sets with analog-only tuners may use other sources of programming e. In the United States, a government-sponsored coupon was available to offset the cost of an external converter box. Analog switch-off of full-power stations took place on December 11, in The Netherlands,  June 12, in the United States for full-power stations, and later for Class-A Stations on September 1, ,  July 24, in Japan,  August 31, in Canada,  February 13, in Arab states, May 1, in Germany, October 24, in the United Kingdom  and Ireland,  October 31, in selected Indian cities,  and December 10, in Australia.
Prior to the conversion to digital TV, analog television broadcast audio for TV channels on a separate FM carrier signal from the video signal.
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This FM audio signal could be heard using standard radios equipped with the appropriate tuning circuits. However, after the transition of many countries to digital TV , no portable radio manufacturer has yet developed an alternative method for portable radios to play just the audio signal of digital TV channels. DTV radio is not the same thing.
The adoption of a broadcast standard incompatible with existing analog receivers has created the problem of large numbers of analog receivers being discarded during digital television transition. Local restrictions on disposal of these materials vary widely; in some cases second-hand stores have refused to accept working color television receivers for resale due to the increasing costs of disposing of unsold TVs.
Those thrift stores which are still accepting donated TVs have reported significant increases in good-condition working used television receivers abandoned by viewers who often expect them not to work after digital transition. In Michigan in , one recycler estimated that as many as one household in four would dispose of or recycle a TV set in the following year. From Wikipedia, the free encyclopedia. Transmission of audio and video by digitally processed and multiplexed signal.
See also: Digital terrestrial television. This article needs additional citations for verification.
Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Main article: 1seg. Further information: Digital television transition. See also: Analog television.