Composite Video Tutorial
Composite Video Explained
Composite video is the picture-only format of an analog television signal before it is combined with a sound signal and modulated onto an RF carrier. Composite video can easily be directed to any broadcast channel simply by modulating the proper RF carrier frequency with it. Most analog home video equipment records a signal in composite format. Laser Discs store a true composite signal, while VHS tapes use a slightly modified composite signal. These devices then give the user the option of outputting the raw signal, or modulating it on to a VHF or UHF frequency to appear on a selected TV channel.
In typical home applications, the composite video signal is typically connected using an RCA jack, normally yellow, and often accompanied with red and white for audio channels. BNC connectors and higher quality co-axial cable are often used in more professional applications.
Some devices that connect to a TV, such as VCRs, naturally output a composite signal. This may then be converted to RF with an external RF modulator that generates the proper carrier. The RF modulator is preferably left outside the console so the RF doesn't interfere with the components inside the machine. VCRs and similar devices already have to deal with RF signals in their tuners, so the modulator is located inside the box.
Modulating RF with the video signal introduces several losses. RF is also noisy due to other broadcasted video and radio signals. Ultimately, RF conversion adds interference to the signal as well. Therefore, it is better to use composite connections instead of RF connections if possible. Further, dot-crawl is an infamous defect that results from crosstalk due to the RF modulation process, and has led to a proliferation of component video systems such as S-Video and component video, which separate the signals.