The following figure shows you a block diagram of the components on the accessDTV PCI card:
The tuner receives the signal from the antenna and tunes in a single channel. The demodulator retrieves the 19.39-Mbps digital stream from the channel. The MPEG decoder decompresses the MPEG encoding and separates subchannels. The signal then goes to either the connectors on the board that connect to a DTV monitor, or to the computer's video card directly. MPEG signals and sound information can go through the PCI bus to the hard disk and sound card, respectively.
The two most important components on the accessDTV card are:
- The digital tuner
- The MPEG-2 decoding system
By connecting a standard UHF/VHF antenna to the accessDTV card, you can tune in any of the 69 DTV channels. (In a typical city, there will be from three to 10 DTV channels on the air.) The tuner pulls the 19.39-Mbps data stream off the channel you choose.
The MPEG-2 decoder circuit decodes this data stream and separates any sub-channels so that you can view them. This is the most important part of the card because it offloads all of the MPEG-2 decoding from your CPU.
The 19.39-Mbps stream is so complex that it would totally consume a Pentium 4 processor running at 1.5 gigahertz (GHz). The accessDTV card contains a custom processor specifically tuned for MPEG-2 decoding. With the accessDTV card handling decompression, only about 5 percent of your computer's CPU power is spent displaying the digital image on the screen. From your computer monitor, you can watch a DTV broadcast in one window and do anything you want in other windows without even knowing that the card is running.
The card also contains a cable-ready and NTSC off-the-air-ready analog tuner. You can connect the coax from your cable system or a standard TV antenna and receive analog channels 2 through 83 as you would on any normal TV. You can also view these channels in a window on your computer screen.