A high-definition television set has an aspect ratio of 16:9 which is the ratio of the width to the height. A standard TV has a 4:3. aspect ratio. HDTVs have higher resolution, meaning they have more pixels or dots of illumination on the screen. Video signals enter an HDTV in various digital or analog formats, but an HDTV creates the high-definition picture out of the signal it receives. Analog video signals travel on RCA cables.
RCA coaxial cables have a center conductor surrounded by an outer shield and can carry signals up to 100 MHz. Since audio and video signals fall withing this range, RCA cables carry them from various signal sources such as VCRs, DVD players, cable and satellite receivers, computers and cameras, to the input jacks on television sets and monitors. The quality of a video signal depends on the originating source. Signals with resolution high enough to be classified as high definition also fall within the range of frequencies that RCA cables can carry. But not all video formats produce these signals.
Analog Video Formats
RCA cables carry both composite and component video signal formats. Composite video mixes all signals for colors, intensity and synchronization onto a single cable, but does not produce signals with resolution high enough to be considered high-definition. Component video carries signals on three RCA cables, and because three cables carry more information than one, component video can send signals with resolution considered high-definition. But the signal source determines the resolution. Sources capable of analog high-definition signals must send them to a TV set in the component video format on three RCA cables.
Any television set is designed with a specific resolution, but an HDTV has either 1,280 x 720 pixels or 1,920 by 1,080. Video signals range from 640 x 480 pixels to 3,840 x 2,400. When an HDTV reads a signal that comes in at its designed resolution, it presents it directly to the screen. If it reads a lower resolution, it up-converts the signal to the designed resolution. If it reads a higher resolution, it down-converts it. Up-converting does not improve the quality of an input signal -- it only expands the signal enough to fill the empty dots on the screen.
HDMI, DVI and Broadcast HDTV
RCA cables carry only analog HDTV in the composite video format. RCA cables can't carry digital HDTV video signals. A digital output from video sources travels via either DVI or HDMI cables that use specialized, multipin connectors. When HDTV signals come from a broadcast station, a cable system or a satellite dish, they are at frequencies much higher than the 100 MHz that RCA cables can carry. These types of HDTV signals need higher-frequency coaxial cables with F type connectors. RCA cables can't carry HDTV signals from an antenna.
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