The Advanced Television Systems Committee (ATSC) is the group that helped to develop the new digital television standard for the United States, also adopted by Canada, Mexico, and South Korea and being considered by other countries. It is intended to replace the NTSC system and produce wide screen 16:9 images up to 1920×1080 pixels in size—more than six times the display resolution of the earlier standard. However, a host of different image sizes are supported, so up to six standard-definition "virtual channels" can be carried in a single broadcast. ATSC also boasts "theater quality" audio because it uses the Dolby Digital (AC-3) format to provide "5.1" surround sound. Numerous auxiliary data services can also be provided.
ATSC coexists with the more widely used DVB standards, and ISDB being implemented in Japan. The system includes the capability to carry PAL- and SECAM-format video (576 displayable lines, 50 fields per second) along with NTSC (480 displayable lines, 60 fields per second) and film (24 frames per second). Broadcasters who use ATSC and must retain an analog signal have to broadcast on two separate channels, as the ATSC system requires use of an entire six megahertz channel. The system has been criticized as being complicated and expensive to implement and use. Many aspects of ATSC are patented, including the AC-3 audio coding, and the VSB modulation. The standards ATSC depends on are often ambiguous, one example would be the EIA-708 standard for closed captioning. 
The data format ATSC is nearly identical to that of Digicipher II, a digital video standard used in satellites (the StarChoice direct-to-home satellite service in Canada, for example).
ATSC "HDTV" Capture Card Questions
What are the differences between the various ATSC capture cards?
Here are the basic stats:
|AirStar (formerly BBTI)|
- F-inputs is the number of selectable F-type inputs (only works on HD-2000 and only with V4L ATSC drivers).
- 8-VSB is the standard for broadcasting ATSC over the air in Canada and the USA.
- QAM64/QAM256 are the two most popular cable tv modulation techniques used by North American cable operators for "Digital Cable"; MythTV can tune both true ATSC broadcasts and any unencrypted digital cable tv you get.
- *The Air2PC can demodulate QAM signals, but can not tune to the frequencies on which most digital cable channels are transmitted, so it is not very useful for digital cable reception.
The reception quality varies somewhat. But the only ones which are noticeably worse than the others are the original pcHDTV card (the HD-2000) and the original Air2PC card. The HD-2000 had noticably weaker reception than the cards made later by pcHDTV and other vendors, while the Air2PC could not reliably tune higher frequencies making it useless for digital cable. Both cards were discontinued when the pcHDTV HD-3000 and the Air2PC HD-5000 were released.
These cards are supported using the DVB drivers for the ATSC portions, and on the cards which support both the NTSC portion is supported by the V4L drivers. The pcHDTV cards have a third driver, a V4L driver for the ATSC portion. While MythTV does support this driver it is best to just forget that it exists, unless you have a HD-2000, since you must choose whether to use the DVB or V4L driver when you set up MythTV. With an HD-2000, you need this driver to support the alternate input.
Can any of these cards work with my satellite receiver?
No. None of the current crop of cards have microcode for decoding QPSK modulated signals, nor do they support DiSEqC signals for controlling your external satellite hardware.
What is all this talk of "use the DVB drivers" for ATSC?
There are two driver subsystems in the Linux kernel for video capture. The original Video4Linux API and the Nokia DVB API. Meanwhile, DVB is a set of European standards for encoding and decoding metadata for MPEG streams for Television, it is exactly equavalent to ATSC standards for encoding and decoding metadata for MPEG streams. Both ATSC and DVB are transmitted over a variety of frequencies, polarizations and modulations. Except for the original DVB driver and the original ATSC driver (which both implemented the V4L interface) all subsequent drivers have used the Nokia DVB API. While the name 'DVB' is very confusing for ATSC users, this does make sense. While the hardware does care about the frequency and modulation and in some cases about the MPEG lowest level packets, the hardware doesn't care a wit about the metadata encoding. So the Nokia DVB API works equally well for ATSC and DVB streams, only MythTV needs to figure out which one it is seeing.
To use the DVB drivers with MythTV, you need to be running a Linux kernel >= 2.6.12, but for some ATSC cards you will need an even newer kernel.
For more information regarding HD3000 DVB setup, including information on the kernel configuration, check out DVB with the pcHDTV HD3000. This article details getting the card to work standalone.