North American broadcast television frequencies
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The North American broadcast television frequencies are on designated television channels numbered 2 through 69, approximately between 54 and 806 MHz. Traditionally, the frequencies are divided into two sections, the very high frequency (VHF) band and the ultra high frequency (UHF) band. The VHF band is further subdivided into two more sections, VHF-Lo (band I) and VHF-Hi (band III). In between lies the FM broadcast band (band II) used for frequency-modulated radio transmissions and a VHF radio band typically used by civil service agencies, amateur radio and aircraft (often called the airband).
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On many FM radios, the audio for channel 6 can often be picked-up by turning the tuner dial below the lower FM band edge, at 87.75. The volume is low as the frequency deviation for TV audio is only ±25 kHz, versus ±75 kHz for FM broadcasting. WRGB attempted to keep this even after putting its digital signal on 6, but it caused destructive interference with the ATSC DTV signal, despite having opposite radio antenna polarizations. The lower sideband of HD Radio signals on 88.1 also overlap slightly from 87.9 to 88.0.
The FM audio carrier is always 4.5 MHz above the VSB video carrier, and the total channel bandwidth is 6 MHz. The video carrier is nominally 1.25 MHz above the lower channel edge. In some cases, analog TV stations are assigned carrier frequency "offsets" of +10 or −10 kHz to minimize interference with distant stations on the same channel (see NTSC for more details). Analog stations must be separated by at least one unused channel except for non-adjacent channel pairs 4 and 5, 6 and 7, and 13 and 14.
Wireless microphones and medical telemetry devices already share some of the TV bands, but transmit at a very low power.
[edit] Changes and variations
Channel 1 was removed early on as a community television reservation and given to amateur radio and other uses. Channels 70 through 83 were removed from the bandplan in the 1980s to make way for AMPS mobile phone service. These channels were mainly used in the U.S., and mainly for broadcast translators, some of which continued in operation if their frequencies were not used by cellular. Channel 37 is allocated to radio astronomy and may not be used by any station.
In the U.S.A., channels 52 through 69 are being reallocated for other purposes as the transition to digital television broadcasting is completed for low-power TV stations. All full-power analog broadcasts ended in June 2009, and all temporary full-power digital broadcasts moved back down to the lower channels. While most other countries abandoned VHF due to its poor suitability for TV broadcasting and allocation for Digital Audio Broadcasting, the FCC chose to cut high-UHF channels instead, because frequency-use rights could be auctioned for a greater price.
Channels 14 through 19 are used for two-way radio in major cities on a non-interference basis, although the transition to digital television (DTV) has caused problems in certain instances when a previously unused channel has begun to be used for DTV broadcasts. The same holds true for wireless microphones and medical telemetry devices in that band.
In most regions, new digital television stations are placed on UHF (14 to 51, except 37 and sometimes 14 and 20) or high-VHF channels (7-13), although others are used in some of the more crowded media markets. With virtual channel numbering, many digital televisions group digital channels with their corresponding analog broadcasts. For example, the first digital TV stream of a station that broadcasts analog TV on channel 4 will usually appear as 4-1 or 4.1 on a DTV receiver, even though the digital transmissions may be on channel 38. Several digital subchannels can be multiplexed together, so 4-1 through 4-5 might be used by one station. Subchannel 0 (e.g., 4-0) designates the analog broadcast. In the U.S., all channels from 7-36 and 38-51 are frequently used for digital TV broadcasts. However, VHF 2 - 6 are rarely used by DTV broadcasters due to ongoing problems with impulse noise, and channel 6 being an adjacent channel to the FM broadcast band.
The VHF bandplan was modified several times before 1948. The last change was the transfer of channel 1, originally intended as a low-power (less than 1,000 watts) LPTV community channel, to two-way land-mobile radio and the six-meter amateur radio band. [1] Amateur television (ATV) is used on four channels in the 420-450 MHz (70-centimeter) amateur band; UHF TV channel 14 starts at 470 MHz. These ATV channels are popular for repeater output and direct communications. ATV is also used on the other amateur bands above 450 MHz.
Note that some channels operate with a frequency offset of 10kHz on the analog video carrier wave, which helps avoid TV interference. Positive-offset station will therefore end in .26, while negative-offset stations will end in .24, and are usually denoted with a plus or minus sign immediately after the number (8+, 37-). While offsets are rare in digital TV, positive-offset stations end in .3380556 while non-offset stations end in .30944056 (rounded to .31).
[edit] VHF original bands (historical)
[edit] VHF bands
Note the upper edge of analog TV 6 slightly overlaps FM channel 200, 87.9MHz. That FM frequency is used by KSFH, various low power pirate stations, and broadcast translator station K200AA (the only USA repeater licensed to use that frequency).
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[edit] UHF band
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- Notes
- The frequencies used by UHF channels 70 through 83 were reallocated to Land Mobile Radio (Public Safety and Trunked Radio) and mobile phones in a CCIR international convention in 1982, and thus were never used for rabbitears digital TV.
- In certain metropolitan areas of the United States, Channels 14 through 20 have been allocated to Land Mobile Radio (LMR) use. [2]
- Channels 52 through 69 in the United States are in the process of being cleared in advance of a similar reallocation once conversion to digital TV has been accomplished.
- 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.
- Cable television frequency issues
- 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).
- Virtual channels 1, 37, and 70 to 99 can be assigned via PSIP even though there is no corresponding physical station on that channel.
[edit] See also
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[edit] External links
- ARRL - TV Channel, CATV and FM Broadcast Frequencies by Kevin K. Custer (W3KKC)
- What ever happened to Channel 1? - J. W. Reiser, based on a Radio-Electronics article of the same name by David A. Ferre.
- Post-transition U.S. digital TV channel assignments as of 1 August 2007
- U.S. cable television channel frequencies
- TVTower.com - Commercial Television Frequencies
