Do you need a box for digital cable?

— -- Question: Comcast is converting my cable TV to all-digital. They say I'll need to get a cable box, but what if I only want to watch the local stations?

Answer: Like many other cable operators, Comcast has been upgrading its local systems from analog to digital over the past few years. This transition — unrelated to the switch to digital over-the-air broadcasts that we finally made in 2009— should free up an enormous amount of bandwidth on its systems for faster Internet access and a wider range of channels.

The "cable-ready" tuners on some analog TVs can't read the stream of ones and zeroes that make up a digital cable feed. If you've been using one to watch standard cable fare like ESPN or the Weather Channel without a box, you'll need a digital-cable adapter— a much smaller add-on than a regular cable box, in many cases free from Comcast— for that set.

But if you own a digital TV and only want to watch local broadcast stations (or public, educational and government channels, but not anything else), you don't need a box or an adapter.

Your DTV should almost certainly include a QAM (" quadrature amplitude modulation") tuner that will allow it to receive those minimum-service channels just by plugging your TV into the nearest cable jack.

Getting entry-level cable this way can be a chore, as I've found. Without the benefit of the usual program-guide interface, those channels can appear in a long, apparently randomly-sorted list — and then, as readers have reported, they may also move around on that list. You also can't get anything beyond those basic channels, because cable operators usually scramble everything else.

Yet QAM tuning does work, even if the occasional service rep may tell you otherwise.

That's not guaranteed to be the case in the future. Following a successful trial by Time Warner Cable in New York, the cable industry has been lobbying the Federal Communications Commission for permission to encrypt these channels as they do the rest of their lineup. QAM tuners, unlike digital-cable adapters or boxes, can't decode scrambled transmissions; in return, cable operators say they could activate service remotely instead of sending a truck to a new subscriber's house.

( Disclosures: One of my freelance clients, the Consumer Electronics Association, has qualms about this proposal. Another, Discovery Communications, owns a few cable channels.)

One possible outcome to this debate, as I noted in a post for CEA, would be to trade QAM encryption for a commitment to support an FCC proposal for box-free TV tuning, called AllVid, that would work with cable and satellite systems alike. That would be terrific. But it would also be years away.

For now, if you want to watch a full set of cable channels without a box — and don't want to have to worry about future QAM encryption or its current hassles — you have basically one option. That's to get a TiVo digital video recorder or one of the handful of other devices to support CableCard reception.

Tip: Don't watch SD versions of your HD channels

If you've paid for an HDTV and a high-def TV package, why put up with a standard-definition version of a channel you already get in much better quality? But that can easily happen when cable or satellite program guides list an SD copy of a channel first, with its HD flavor somewhere up in the 300s, 400s or 800s on the guide.

Some TV providers have realized this problem. Cablevision's HD boxes, for example, tune in HD versions of network channels even if you select the single-digit numbers traditionally reserved for their SD identities. DirecTV provides a " hide SD duplicates" setting among its program-guide options. And Comcast's latest guide features a "Watch in HD" button that should alert you when a program is available in high-def on another channel.

In other cases, you'll have to hide SD channels from your program guide (such as on AT&T's U-Verse) or set up a favorites list of HD channels that excludes their low-resolution siblings (for instance, on Verizon's Fios TV).

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Rob Pegoraro is a tech writer based in Washington, D.C. To submit a tech question, e-mail Rob at rob@robpegoraro.com. Follow him on Twitter at twitter.com/robpegoraro.