TV tuners are devices for your computer that allow you to decode television transmissions and process them in a digital manner on your computer ie. to watch or record.

There are three main methods for transmitting a television signal:

1. Terrestrial transmission uses wireless radio signals, usually in the VHF/UHF bands, which are received using an RF aerial.
2. Satellite transmission is also a wireless radio signals, which are received using a correctly positioned satellite dish.
3. Cable transmission is a direct wired connection.

There are two main types of television signal:

1. Analog encoding was, until recently, the most common method for transmitting TV. Various formats were used throughout the world, including NTSC, PAL and SECAM. It has been used on all transmission media, but primarily on terrestrial. It is susceptible to noise and interference.
2. Digital encoding is becoming the new standard for TV transmission. It is also called DVB - digital video broadcast. There are DVB formats for terrestrial (DVB-T and DVB-H), cable (DVB-C), satellite (DVB-S). It is more resilient to inteference and uses up less radio spectrum.

Analog tuners for your PC are usually in the form of a PCI/Cardbus card or USB device. They usually have an analog signal input (most commonly RF terrestrial) and maybe also some composite or s-video inputs for capturing analog recordings from a camera or VCR.

Digital (DVB) tuner devices are available as PCI/PCIe/Cardbus cards, or USB/USB2 devices. Different models exist to support the various DVB types, such as DVB-T, DVB-C and DVB-S.

Hybrid devices support both analog and digital signals. Some models share a physical tuner, and can not use the analog and digital parts at the same time. Other models have two tuners which allow both analog and digital to be used simultaneously.

There are now multiple tuner devices available, with up to 2, 4 or 8 physical tuners. These are available in different combinations of analog, DVB-T, DVB-C and DVB-S connections.

There are two main types of physical tuners:

1. Can tuners are the traditional physcial tuner used on TV cards. They can be identified as a large metallic shielded box on the device, near the signal input connector. Tuning to RF signals is a complicated process and miniaturising the components has proven difficult. These can tuners can get very hot when used continuously.
2. Silicon tuners are becoming much more common. New technologies have enabled RF tuning to be done on a silicon chip. This is much cheaper to produce and is smaller and runs cooler. There is still debate as to whether the quality of the resultant signal and tuning speed is as good as can tuners. If you have a small TV tuner, such as USB or PCMCIA, chances are that it is a new silicon tuner.
   

So when purchasing a tuner card it is important to identify whether you require analog, DVB-T, DVB-C, DVB-S, or a combination thereof.