1. Digital TV Seeks Parity With Analog TV In The Tuner Card World

As of July 1, 2006, the FCC has mandated that all new TVs with a 25" or larger display include a digital ATSC tuner for digital broadcasts, including HDTV signals. As of this year, the same mandate applies to all sets 13" or larger. This new tuner requirement anticipates the so-called "digital cutover" currently set for February 17, 2009, at which time all analog TV broadcasts must be abandoned in favor of digital broadcasts. Though this doesn’t affect cable or satellite companies, because they don’t broadcast their content over the air, this nevertheless presages a clear change in technology for how TV signals are represented, transmitted and received.

It also explains why we’ve seen a steady move from all the major TV tuner card vendors to add ATSC tuners and capabilities to their offerings, especially in the past 18 months. There has been an increasing number of so-called "combo card" offerings coming to market in the past six months. The combo card designation reflects a design that includes dual tuners, one for NTSC or old-fashioned analog TV signals, and another for ATSC or new-fangled digital TV signals, including HDTV. We take a look at three of them, after we take a brief technology detour to explain why those with digital cable TV service may find these products particularly appealing, especially those with high-definition TV sets or other forms of HDTV playback capability.

The Joy Of "Clear QAM"

QAM stands for quadrature amplitude modulation, and describes a signal transport scheme based on changing the amplitude of two related carrier waves. The two sinusoid carrier waves are kept 90 degrees out of phase with each others, which earns them the technical designation of quadrature carriers, and explains the name that adheres to the scheme.

QAM schemes use so-called constellation diagrams to represent specific signal patterns, where a number of data points that are radially symmetrical around a central axis map very nicely into Cartesian coordinates. For digital signals, in fact, QAM constellations fit into square grids with equal vertical and horizontal spacing, where the number of data points fits some binary number. Common digital QAM forms include 16-QAM, 64-QAM, 128-QAM, and 256-QAM, where 62-QAM and 256-QAM schemes are widely used for cable TV applications. Because HDTV requires higher bandwidth, it should be reasonably intuitive that it be associated with 256-QAM.

256-QAM earns the "clear QAM" designation when it applies to television signals sent unscrambled via cable TV broadband to subscribers ("in the clear," in other terms). Because 256-QAM and ATSC OTA tuners share many similar characteristics, a great many of the ATSC tuner chips also integrate 256-QAM capabilities as well. What this means to viewers is that those who subscribe to digital cable TV services can use an ATSC tuner with 256-QAM capabilities to pick up and decode digital cable TV channels, including HDTV channels, which are unscrambled without even requiring a cable box to process incoming signals.

That said, the reason this technology is called "clear QAM" is because it cannot handle scrambled or encrypted signals commonly associated with premium channels or pay-per-view programming that is also available from cable TV companies (satellite TV uses a different form of signaling called differential phase shift keying or DPSK, which is not compatible with QAM). To handle those kinds of signals, you must either have a special digital set-top box from your cable provider, or a CableCard and compatible devices. To make a long and occasionally depressing story incredibly short, a workable solution for TV capture cards and scrambled or encrypted HDTV signals has yet to be developed.

While there are those who argue that CableCard solutions offer a remedy, we hasten to point out that they require users to lease CableCard devices from some cable provider, and that CableCard socketing devices (and the licenses that go with them) are available only to OEMs for sale to end users in consumer hardware. There’s no such thing as "do-it-yourself" when it comes to capturing encrypted HDTV content for playback, recording, or both uses in a PC of your choosing. The only way to acquire such a capability is to purchase a PC, DVR or TV set already equipped with the necessary circuitry to accommodate one or more CableCards, and then to acquire those CableCards from a local service provider.

Furthermore, each CableCard is tied to a specific PC. This means you can’t simply cannibalize the hardware from one PC and move it to another, thanks to some clever and powerful hardware checks performed each time the CableCard circuitry is started up in some machine or playback device. Until and unless other options become available, CableCard products must be considered turnkey solutions, deliberately designed to foil system builders who’d rather put their own components together.

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