TV tuner card
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A TV tuner card is a computer component that allows television signals to be received by a computer. Most TV tuners also function as video capture cards, allowing them to record television programs onto a hard drive.
While typically a PCI-bus expansion card, they can also be a USB device. Some video cards double as TV tuners, notably the ATI All-In-Wonder series. The card contains a receiver, tuner, demodulator, and a analog-to-digital converter for analog TV. Like TV sets, each version is designed for the radio frequencies and video formats used in each country. However, many TV tuners used in computers use DSP, so a firmware upgrade is often all that's necessary to change the supported video format. Many newer TV tuners have flash memory big enough to hold the firmwares for decoding several different video formats, making it possible to use the tuner in many countries without having to flash the firmware. In addition to the frequency tuner, many include a composite video input. Many TV tuners can function as FM radios: this is because the FM radio spectrum lies between television channels 6 and 7, and the DSP can be easily programmed to decode FM.
Some provide DVB reception for digital radio, television or data signals (either with or without hardware MPEG decoding capability); these may be used to receive satellite broadcasts but normally provide no analogue input capability.
Most internal tuners do all the low level demodulation needed to convert a radio signal into an on-screen image using a hardware DSP chip or ASIC; some also have hardware MPEG encoders and use DMA to bypass the CPU entirely. Some cheaper tuners don't have much in the way of onboard signal processing and rely on the system's CPU for that task. External tuners may convert the signal into either a video stream suitable for display on the screen, or to an intermediate format such as MPEG; in either case, the CPU is needed to direct the image onto the screen.
TV tuners supporting digital television broadcasts eventually became available; a tuner displaying an HDTV image on a computer monitor is typically much cheaper than a dedicated high-definition television system, but with a smaller physical screen. Broadcasts can also be digitally recorded by the computer for later replay, or distribution (illegal in many countries) to other computer users.
There is one more PCI card which will act as television receiver (a.k.a Set-top box) - This will be based on DVB and can deliver MPEG-1, MPEG-2, MPEG-4 or DivX content. This is also known as Digital television adapter
The hardware on television cards is often very generic radio receiving hardware. Because of this, cards based on the SAA7134 chip have successfully been used to receive FM broadcasts in the UHF region (such as from emergency services). For example, see this article.
Makers of TV tuner/capture cards
- ATI Technologies
- Formac - TV Tuners for Macintosh
- Micro-Star International (MSI)
- Pinnacle Systems
- Zurotech - TV Tuner for PCMCIA