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Each television channel occupies a range within the radio spectrum.
This range is specified by a set of frequencies.
The frequency ranges of standard TV channels are 54 Mhz to 216 Mhz for VHF, and 470 Mhz to 806 Mhz for UHF.
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The range for UHF includes channels 2 to 13, and VHF includes channels 14 to 69.
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Standard TVs use channels 2 through 69, HDTVs will use channels 7 through 51.
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The amount of space the channel takes within one of the two ranges (UHF or VHF), is its bandwidth.
Each channel occupies 6 Mhz of bandwidth.
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On a standard TV, this bandwidth allows for 525 scan lines.
The two HDTV formats are interlaced, at 1080 scan lines, and progressive, at 720 scan lines.
An HDTV operating in the 1080 mode can display transmissions broadcast in the 720 mode.
The image will fill the screen, but the pixels will be larger.
An HDTV operating in the 720 mode can display transmissions broadcast in the 1080 mode.
To show these images, the set drops every third line from the screen, as well as a small amount from each side.
The relationship between the width of a scan line and the number of scan lines is refered to as the aspect ratio.
Standard TV uses 4:3 (read 4 by 3), where as HDTV uses 16:9.
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Each line of an HDTV contains 1920 horizontal pixels compared to the 720 horizontal pixels in standard TV.
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A pixel on a standard TV is rectangular, being taller than it is wide.
On an HDTV screen, the pixels are smaller and sqaure.
This means that it takes four and a half HDTV pixels to make one standard TV pixel.
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In Japan, HDTV uses 20 Mhz, in the US, it occupies the same 6 Mhz as analog.
This is accomplished thru MPEG-2 data compression.
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The FCC has mandated that all analog TV transmissions must end in 2006.
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TV Stations broadcasting in digital.
