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North American broadcast television frequencies
In North America, terrestrial television is broadcast on designated channels numbered 2 through 69. Except for a few instances, consumer televisions and recorders come with these frequencies pre-programmed in, as opposed to what sometimes occurs in other places around the world. Traditionally, the frequencies are divided into two sections, the very high frequency (VHF) band and the ultra high frequency (UHF) band, but in reality, the VHF band is further subdivided into two more sections, VHF-Lo (band I) and VHF-Hi (band III). In between lies the FM 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).
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 quite low as the deviation or modulation for TV audio is only ±25 kHz, versus ±75kHz for FM broadcasting.
Channels 70 through 83 were removed from the bandplan in the 1970s to make way for AMPS cellular telephone service; these channels were mainly used in the U.S., and mainly for 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.
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 many regions, new digital TV channels are placed on channels 7-13, 15-19, 21-36 and 38-51, although others are used in some of the more crowded television 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.
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 the six-meter amateur radio band.  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.
The FM audio carrier is always 4.5 MHz above the VSB video carrier, and the total channel bandwidth is 6MHz. 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. Digital TV is much more resistant to interference than NTSC, so it can operate adjacent to any station. This permits much greater utilization of the TV broadcast spectrum, allowing the reallocation of many TV channels to other services.
Note that FM channel 200, 87.9MHz, overlaps TV 6. This is used only by KSFH and K200AA.
* Channel(s) no longer allocated to broadcast television
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "North_American_broadcast_television_frequencies". A list of authors is available in Wikipedia.|