North American television frequencies are different for over-the-air (also called terrestrial) and cable television systems. Over-the-air television channels are divided into two bands: the VHF band which comprises channels 2 through 13 and occupies frequencies between 54 and 216 MHz, and the UHF band, which comprises channels 14 through 83 and occupies frequencies between 470 and 890 MHz. These bands are different enough in frequency that they often require separate antennas to receive (although many antennas cover both VHF and UHF), and separate tuning controls on the television set. The VHF band is further divided into two frequency ranges: VHF low band (Band I) between 54 and 88 MHz, containing channels 2 through 6, and VHF high band (Band III) between 174 and 216 MHz, containing channels 7 through 13. The wide spacing between these frequency bands is responsible for the complicated design of rooftop TV antennas. The UHF band has higher noise and greater attenuation, so higher gain antennas are often required for UHF.
Maps, Directions, and Place Reviews
Broadcast television
History
The VHF band plan was modified several times before 1948. The last of these changes was the deletion of channel 1, originally intended as a community channel. This allocation of the spectrum was given to two-way land-mobile radio.
UHF channels 70-83 in the United States were reallocated in 1983. As of 2016, channels 52-69 are not available for normal, high-power digital television broadcasting in the United States, but some channels are available for use as low-power or translator stations.
In March 2008, the FCC requested public comment on turning the bandwidth currently occupied by analog television channels 5 and 6 (76-88 MHz) over to extending 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.
700 MHz band
Wireless microphones and medical telemetry devices formerly shared some of the TV bands, but transmitted at a very low power. After the migration of digital television in 2009, the Federal Communications Commission (FCC) banned these from using the 700 MHz band in the U.S., effective June 12, 2010. The 700 MHz band is now used for public safety communications and wireless broadband providers.
600 MHz band
In 2015 the FCC has announced the possible auction of all remaining spectrum including and above channel 38. Such decision would require the reconfiguration of channel allotment (known in the broadcast TV industry as the channel "repack"), and would allow for higher gain small antennas. This could preclude the auction of some or all remaining VHF or UHF spectrum, a decision that would then allow further yet smaller high gain antennas. In April 2017, it has since been decided that channels 38 and above will be deleted, but channel 37 remains reserved.
Channel frequencies
VHF band
UHF band
The following table lists over-the-air television channels in the ultra high frequency band. Some entries have a colored background, indicating that the channels have been reallocated for other use. The notes below the table explain the re-allocations.
Notes
- Channel 37 is reserved for radio astronomy in the United States, Canada, Bermuda and the Bahamas, thus there are no television stations assigned to it. Mexico also informally observes a ban on transmitters using this channel.
- 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. Later that year (on December 16, 2011), Industry Canada and the CRTC followed suit in placing a moratorium on future television stations using Channel 51 for broadcast use for the same reason.
- Channels 52 through 69 in the United States have been reallocated now that conversion to digital TV was completed on June 12, 2009, although some low-power and translator stations may still be in use on these channels.
- The frequencies used by UHF channels 70 through 83 were reallocated to the Land Mobile Radio System (Public Safety and Trunked Radio) and mobile phones in a CCIR worldwide convention in 1983.
- With the advent of digital television in 2009, stations are allowed to identify themselves by a virtual channel that may not necessarily be the same as the station's RF channel. Virtual channels 1, 37, and 70 to 99 can be assigned via PSIP even though there is no corresponding physical station on that RF channel.
- UHF channels 14 to 43 translate to common cable-ready channels 65 to 94 (add 51).
- UHF channels 44 to 69 translate to rarely used cable TV channels 100 to 125 (add 56).
- Cable-ready channels 6, 95, 96, and 97 have audio carriers which overlap FM radio stations (87.7 ,95.7, 101.7 and 107.7).
Historical band plans
Tv Carriers In My Area Video
Cable television
Harmonically-related carriers (HRC) is a system for assigning television channel numbers to bands of frequencies over a cable TV network. William Grant, in his book, states:
"By harmonically relating the carrier frequencies themselves it is ... possible to improve system performance. This does not reduce the beats produced, but positions them within the system transmission spectrum, such that they are more tolerable. In effect, all signal carriers are spaced precisely at 6 MHz apart, and thus, all beats generated are at 6 MHz increments." "Since the television signals are vestigial sideband modulation, if the beat products can be manipulated to fall on or near the RF carriers themselves, they are much less offensive."
Incrementally-related carriers (IRC) is a system for assigning television channel numbers to bands of frequencies over a cable TV network. The IRC plan attempts to minimize distortion products by deriving all video carrier signals from a common source. The IRC system assigns channel frequencies (for the North American NTSC-M system) spaced 6 MHz apart. In an IRC system, the VHF channels are at their off-air frequencies except for channels 5 and 6, which will be 2 MHz higher than usual.
Channel frequencies
These frequencies are used for both NTSC-based analog television and QAM-based digital television. Band plans for North American cable television systems are standardized in EIA standard 542-B.
Channels 57 to 61, and 143 to 145, are used in amateur television.
Channel usage
Cable channels 98 and 99 (A2 and A1, 108-120 MHz), if used, have appeared as channel 00 and 01 respectively on some cable boxes.
Source of the article : Wikipedia
EmoticonEmoticon