What Is an External Tuner?by Aaron Parson
In order to view a specific TV channel, your television or computer needs to tune into the channel, separating its signal from the data of all the other channels. This requires a TV tuner, which can either come built into a TV or computer -- an internal tuner -- or as a separate device, called an external tuner. Cable and satellite companies generally provide or rent external tuners for TVs, while computer tuners are often sold separately.
External Tuners for Television Sets
Many televisions have built-in tuners, allowing them to tune in to channels received through the antenna or, on some cable systems, basic cable channels. Other types of TV signals, including digital cable and satellite, require an external tuner, in the form of a set-top box. Standard definition tuners usually connect to TVs or home theater systems with coaxial cable, while high definition tuners require either an HDMI cable or a set of component cables. Some HD tuners also support a DVI connection, but this method carries only the video signal without audio.
External Computer TV Tuners
While regular TV tuners connect directly to a television or home theater system, you can also buy tuners that plug into a USB port, allowing you to watch and record TV on your computer. If your TV signal comes directly from a coaxial port in the wall or from a digital antenna, you can use a tuner with a coaxial port on one end and a USB plug on the other. If your cable or satellite service requires a set-top box, however, you need to connect the set-top box to a tuner with video input ports, just as you would connect it to a TV.