Digital channel election
Encyclopedia
A digital channel election was the process by which television station
s in the United States
chose which physical radio-frequency TV channel they would permanently use after the analog shutdown
in 2009. The process was managed and mandated by the Federal Communications Commission
for all full-power TV stations. low-powered television (LPTV) stations are going through a somewhat different process, and are also allowed to flash-cut
to digital.
did not have the first option, as the FCC and then the U.S. Congress revoked them from the bandplan
.
Many stations have chosen to keep their new channels permanently, after being forced to buy all new transmitter
s and television antenna
s. In some cases where the station's current analog tower could not handle the stress of the new digital antenna's weight and wind load, station owners had to construct entirely new broadcast towers in order to comply with the FCC's DTV mandate.
Most broadcasters were bitter at having to purchase digital equipment and broadcast a digital signal when very few homeowners had digital television set
s. The FCC allowed broadcasters the opportunity to petition the Federal Communications Commission
(FCC) for special temporary authority
(STA) to operate their digital facilities at low power, thereby allowing broadcasters additional time in which to purchase their full-power digital facilities. However, the FCC gave a stern July 2006 deadline for all full-power television stations to at least replicate 80% of their current analog coverage area, or run the risk of losing protection
from encroachment by other stations.
Most stations made an election in the first round, and most of those received their requested channels. Applicant conflicts with neighboring stations had to request a different channel in the second round. The third and final round occurred in May 2006.
Some stations requested that the FCC assign the best available channel.
of the radio spectrum
. These affect the radio propagation
of DTV just as with other signals.
The low VHF channels from 2 to 6, while requiring the lowest power (up to 100 kW analog video or 20 kW digital), are prone to electromagnetic interference
. The ATSC
digital TV system has severe problems with susceptibility to impulse noise
, bursts of interference which briefly render the entire channel unusable, due to its inability to instantaneously determine where in a video frame to resume display when the signal returns. The result is macroblock
ing and pixelation
of the entire signal whenever impulse noise sources (such as motors
, appliances or electrical storm
s) are active. They also are the lowest in frequency
and therefore the longest in wavelength
, requiring the largest antennas both to transmit
and receive. They are also prone to atmospheric ducting, especially at night
when the ground
(and the air near it) cools rapidly. Because of the antenna size (a properly-sized VHF TV 2 dipole
spans approximately eight feet) and the fact that there are only five channels in this band, most set-top antennas are designed to receive the higher TV bands.
Furthermore, channel 6 abuts the FM broadcast band
at 88 MHz, possibly causing and receiving interference
from adjacent channel
s. (The FCC refused to remove this band from the bandplan, because taking the high UHF channels instead would bring in more money at auction
. This also contradicts what has been done in every other country that has forced a DTV transition, all giving up the VHF bands.) A completely unaddressed issue is the use of HD Radio
on 88.1 FM
, where the lower sideband
overlaps the far upper sideband of digital TV channel 6.
The upper VHF (band III
), including channels 7 to 13, is better about the above problems, but still not as good as the UHF band. By keeping these for TV, it also prevents the use of the band for Digital Audio Broadcasting
, as is done with local radio station
s in Europe
.
The UHF band contains 55 channels from 14 to 69, which excludes channel 37
in the U.S. Channels 52 to 69 are unavailable for digital TV, on a permanent basis, leaving only 37 channels. Stations generally try to choose a lower frequency, which causes some crowding and therefore election conflicts on the lowest channels. Still, the UHF band has great advantages over VHF, in large part because of its propagation characteristics and lack of impulse noise
. The shorter wavelength also means that smaller antennas are needed, an advantage for both the broadcaster
and the viewer. Another advantage is that the great majority of stations use this band, requiring only one type of antenna (and sometimes amplifier
) to receive all of those stations. Key disadvantages of UHF operation include the need for greater transmitter power and the reduced coverage area; the edge diffraction
of signals around terrestrial obstacles degrades rapidly as frequency is increased.
numbering will keep stations appearing on their original analog channel numbers, except the times that a station has trouble transmitting PSIP metadata
.
However, most ATSC tuner
s must re-scan
for stations that change their RF channel. On some this is as simple as manually punching-in the new RF channel, at which point the decoder will read the PSIP data and re-map to the proper channel number. However, this may not delete the original mapping, leaving the original "dead" channels interleaved with the new ones (such as 5.1 old, 5.1 new, 5.2 old, 5.2 new), or possibly confusing the receiver (and the user). In many cases, a receiver will not automatically add the new mapping at all if an old one exists. Completely re-scanning will normally solve this, but may not pick-up stations that are weak or temporarily off-air during the scan, causing the need to manually enter them (if this is even possible with the given receiver).
Where stations are moving to a different frequency band (such as UHF to VHF), this will affect antenna
selection. Many antennas marketed for HDTV use are UHF-only or perform poorly on VHF, while many 82-channel VHF/UHF antennas are a compromise design strongly favoring VHF channels.
Television station
A television station is a business, organisation or other such as an amateur television operator that transmits content over terrestrial television. A television transmission can be by analog television signals or, more recently, by digital television. Broadcast television systems standards are...
s in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
chose which physical radio-frequency TV channel they would permanently use after the analog shutdown
DTV transition in the United States
The DTV transition in the United States was the switchover from analog to exclusively digital broadcasting of free over-the-air television programming...
in 2009. The process was managed and mandated by the Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
for all full-power TV stations. low-powered television (LPTV) stations are going through a somewhat different process, and are also allowed to flash-cut
Flash-cut
A flash-cut, also called flash-cutover, is an immediate change in a complex system, with no phase-in period.Some telephone area codes were split immediately, rather than being phased in with a permissive dialing period. An example is telephone area code 213, which was split into 213 and 714 all at...
to digital.
Process
Stations could choose to keep their initial digital TV channel allocation, do a flash-cut to their former analog TV channel, or attempt to select another channel, often an analog channel or pre-transition digital channel from another station that had been orphaned. Stations on channels 52 to 69Band V
Band V is the name of a radio frequency range within the ultra high frequency part of the electromagnetic spectrum. It is not to be confused with the V band in the extremely high frequency part of the spectrum....
did not have the first option, as the FCC and then the U.S. Congress revoked them from the bandplan
Bandplan
A bandplan or band plan is a plan for using a particular band of radio frequencies, that are a portion of the electromagnetic spectrum . Each bandplan defines the frequency range to be included, how channels are to be defined, and what will be carried on those channels...
.
Many stations have chosen to keep their new channels permanently, after being forced to buy all new transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
s and television antenna
Television antenna
A television antenna, or TV aerial, is an antenna specifically designed for the reception of over the air broadcast television signals, which are transmitted at frequencies from about 41 to 250 MHz in the VHF band, and 470 to 960 MHz in the UHF band in different countries...
s. In some cases where the station's current analog tower could not handle the stress of the new digital antenna's weight and wind load, station owners had to construct entirely new broadcast towers in order to comply with the FCC's DTV mandate.
Most broadcasters were bitter at having to purchase digital equipment and broadcast a digital signal when very few homeowners had digital television set
Television set
A television set is a device that combines a tuner, display, and speakers for the purpose of viewing television. Television sets became a popular consumer product after the Second World War, using vacuum tubes and cathode ray tube displays...
s. The FCC allowed broadcasters the opportunity to petition the Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
(FCC) for special temporary authority
Special temporary authority
In U.S. broadcast law, a special temporary authorization or special temporary authority is a type of broadcast license which temporarily allows a broadcast station to operate outside of its normal technical or legal parameters...
(STA) to operate their digital facilities at low power, thereby allowing broadcasters additional time in which to purchase their full-power digital facilities. However, the FCC gave a stern July 2006 deadline for all full-power television stations to at least replicate 80% of their current analog coverage area, or run the risk of losing protection
Service contour
In US broadcasting, service contour refers to the area in which the Federal Communications Commission predicts and allows coverage....
from encroachment by other stations.
Most stations made an election in the first round, and most of those received their requested channels. Applicant conflicts with neighboring stations had to request a different channel in the second round. The third and final round occurred in May 2006.
Some stations requested that the FCC assign the best available channel.
Considerations
Aside from the practical considerations above, there are also technical considerations which are based on the physicsPhysics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
of the radio spectrum
Radio spectrum
Radio spectrum refers to the part of the electromagnetic spectrum corresponding to radio frequencies – that is, frequencies lower than around 300 GHz ....
. These affect the radio propagation
Radio propagation
Radio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere...
of DTV just as with other signals.
The low VHF channels from 2 to 6, while requiring the lowest power (up to 100 kW analog video or 20 kW digital), are prone to electromagnetic interference
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
. The ATSC
ATSC
ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....
digital TV system has severe problems with susceptibility to impulse noise
Impulse noise
Impulse noise could mean:*impulse noise *Electromagnetic interference*Burst noise...
, bursts of interference which briefly render the entire channel unusable, due to its inability to instantaneously determine where in a video frame to resume display when the signal returns. The result is macroblock
Macroblock
Macroblock is an image compression component and technique based on discrete cosine transform used on still images and video frames. Macroblocks are usually composed of two or more blocks of pixels. In the JPEG standard macroblocks are called MCU blocks....
ing and pixelation
Pixelation
In computer graphics, pixelation is an effect caused by displaying a bitmap or a section of a bitmap at such a large size that individual pixels, small single-colored square display elements that comprise the bitmap, are visible to the eye...
of the entire signal whenever impulse noise sources (such as motors
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
, appliances or electrical storm
Electrical storm
Electrical storm may refer to:* A thunderstorm* A medical condition of chaotic electrical activity of the heart, usually manifested by ventricular tachycardia* "Electrical Storm" , song by U2...
s) are active. They also are the lowest in frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
and therefore the longest in wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
, requiring the largest antennas both to transmit
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
and receive. They are also prone to atmospheric ducting, especially at night
Night
Night or nighttime is the period of time when the sun is below the horizon. This occurs after dusk. The opposite of night is day...
when the ground
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
(and the air near it) cools rapidly. Because of the antenna size (a properly-sized VHF TV 2 dipole
Dipole
In physics, there are several kinds of dipoles:*An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some distance. A permanent electric dipole is called an electret.*A...
spans approximately eight feet) and the fact that there are only five channels in this band, most set-top antennas are designed to receive the higher TV bands.
Furthermore, channel 6 abuts the FM broadcast band
FM broadcast band
The FM broadcast band, used for FM broadcast radio by radio stations, differs between different parts of the world. In Europe and Africa , it spans from 87.5 to 108.0 megahertz , while in America it goes only from 88.0 to 108.0 MHz. The FM broadcast band in Japan uses 76.0 to 90 MHz...
at 88 MHz, possibly causing and receiving interference
Adjacent-channel interference
Adjacent-channel interference is interference caused by extraneous power from a signal in an adjacent channel. ACI may be caused by inadequate filtering , improper tuning or poor frequency control .ACI is distinguished from crosstalk.Broadcast...
from adjacent channel
Adjacent channel
In broadcasting an adjacent channel is an AM, FM, or TV channel that is next to another channel. First-adjacent is immediately next to another channel, second-adjacent is two channels away, and so forth. Information on adjacent channels is used in keeping stations from interfering with one...
s. (The FCC refused to remove this band from the bandplan, because taking the high UHF channels instead would bring in more money at auction
Auction
An auction is a process of buying and selling goods or services by offering them up for bid, taking bids, and then selling the item to the highest bidder...
. This also contradicts what has been done in every other country that has forced a DTV transition, all giving up the VHF bands.) A completely unaddressed issue is the use of HD Radio
HD Radio
HD Radio, which originally stood for "Hybrid Digital", is the trademark for iBiquity's in-band on-channel digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their analog signals...
on 88.1 FM
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
, where the lower sideband
Sideband
In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, containing power as a result of the modulation process. The sidebands consist of all the Fourier components of the modulated signal except the carrier...
overlaps the far upper sideband of digital TV channel 6.
The upper VHF (band III
Band III
Band III is the name of a radio frequency range within the very high frequency part of the electromagnetic spectrum.Band III ranges from 174 to 230 MHz, and it is primarily used for radio and television broadcasting...
), including channels 7 to 13, is better about the above problems, but still not as good as the UHF band. By keeping these for TV, it also prevents the use of the band for Digital Audio Broadcasting
Digital audio broadcasting
Digital Audio Broadcasting is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format....
, as is done with local radio station
Radio station
Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...
s in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
.
The UHF band contains 55 channels from 14 to 69, which excludes channel 37
Channel 37
Channel 37 is an unused television channel in countries using the M and N broadcast television system standards. Channel 37 occupies a band of UHF frequencies from 608 to 614 MHz, frequencies that are particularly important to radio astronomy...
in the U.S. Channels 52 to 69 are unavailable for digital TV, on a permanent basis, leaving only 37 channels. Stations generally try to choose a lower frequency, which causes some crowding and therefore election conflicts on the lowest channels. Still, the UHF band has great advantages over VHF, in large part because of its propagation characteristics and lack of impulse noise
Impulse noise
Impulse noise could mean:*impulse noise *Electromagnetic interference*Burst noise...
. The shorter wavelength also means that smaller antennas are needed, an advantage for both the broadcaster
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
and the viewer. Another advantage is that the great majority of stations use this band, requiring only one type of antenna (and sometimes amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
) to receive all of those stations. Key disadvantages of UHF operation include the need for greater transmitter power and the reduced coverage area; the edge diffraction
Knife-edge effect
In electromagnetic wave propagation, the knife-edge effect or edge diffraction is a redirection by diffraction of a portion of the incident radiation that strikes a well-defined obstacle such as a mountain range or the edge of a building....
of signals around terrestrial obstacles degrades rapidly as frequency is increased.
Effects
Channel elections generally will not affect consumers in the long run, because virtual channelVirtual channel
In telecommunications, a logical channel number , also known as virtual channel, is a channel designation which differs from that of the actual radio channel on which the signal travels....
numbering will keep stations appearing on their original analog channel numbers, except the times that a station has trouble transmitting PSIP metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
.
However, most ATSC tuner
ATSC tuner
An ATSC tuner, often called an ATSC receiver or HDTV tuner is a type of television tuner that allows reception of digital television television channels transmitted by television stations in North America, parts of Central America and South Korea that use ATSC standards...
s must re-scan
Scan
Scan may refer to:Acronyms:*Schedules for Clinical Assessment in Neuropsychiatry , a psychiatric diagnostic tool developed by WHO*Shared Check Authorization Network , a database of bad check writers and collection agency for bad checks...
for stations that change their RF channel. On some this is as simple as manually punching-in the new RF channel, at which point the decoder will read the PSIP data and re-map to the proper channel number. However, this may not delete the original mapping, leaving the original "dead" channels interleaved with the new ones (such as 5.1 old, 5.1 new, 5.2 old, 5.2 new), or possibly confusing the receiver (and the user). In many cases, a receiver will not automatically add the new mapping at all if an old one exists. Completely re-scanning will normally solve this, but may not pick-up stations that are weak or temporarily off-air during the scan, causing the need to manually enter them (if this is even possible with the given receiver).
Where stations are moving to a different frequency band (such as UHF to VHF), this will affect antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
selection. Many antennas marketed for HDTV use are UHF-only or perform poorly on VHF, while many 82-channel VHF/UHF antennas are a compromise design strongly favoring VHF channels.