The DTV transition: The low-down on analog pass-through

Most TV stations must stop broadcasting analog signals on February 17, 2009, but some stations don't have to switch completely to digital broadcasts. Low-power TV stations, TV translator stations, and so-called Class A stations can continue broadcasting analog TV signals well after the deadline. If you're in an area served by such a station, you'll want a DTV converter box that can handle both digital and analog signals. Of course, if you're not able to receive any digital stations, there's no rush to buy any converter box, and we anticipate there being a greater assortment of boxes with analog pass-through in the not-too-distant future.

Low-power TV was created in the early 1980s to provide locally oriented or specialized programming to smaller rural towns or small communities within urban areas. TV translator stations boost and re-broadcast the signals of full-power stations to communities that can't receive them either because they're too far away, or because mountains or uneven terrain inhibit reception. Class A stations are a class of low-power stations that are required to air a certain amount of locally produced programming each week.

The vast majority of TV broadcasts are from full-power stations that will switch to digital, but nearly 7,000 low-power and translator stations provide free over-the-air TV programming to viewers. Although they will one day, too, have to make the switch to digital, currently there's no firm timetable for that transition. Therefore, if you're in a market currently being served by such a station, we recommend you get a DTV converter box with "analog pass-though" capability. These boxes allow analog TV signals to pass through the box without being converted to digital so the TV's analog tuner can receive and display them. We recently ran preliminary tests on one of the early pass-through models, the Philco TB100HH9. We'll be posting that review here shortly.

There are a few ways to determine if you're being served by one of these types of stations. Most low-power stations typically have call letters that end in –LP (such as WAOH-LP); some have five characters starting with the letters K or W, followed by two numbers and two additional letters (W35AX, for example). A translator station uses a similar designation, with its channel number in the middle of its call letters. You're viewing a translator station if you're watching a full-power station but have to tune to another channel to watch it. And Class A stations can typically be identified by the use of a –CA suffix. The National Telecommunications and Information Administration (NTIA), the agency administering the DTV converter box coupon program, has online a complete list of low-power and translator stations.

According to the NTIA, there are currently six approved converter boxes with analog pass-through capability. They are:

• Digital Stream DX8700
• Digital Stream DSP7700T
• EchoStar TR-40
• Magnavox TB-100MG9
• Philco TB100HH9 (seen at right)
• Philco TB150HH9

The NTIA maintains a list of all approved converter boxes online. (Models with analog pass-through have an asterisk next to them. We've previously previewed three DTV converter boxes (without analog pass-through): the Magnavox TB100MW9, Insignia NS-DXA1, and Zenith DTT900 (seen above, left). For more information on what else you need for digital TV on your analog set, see our previous post, "How to use a converter box & antenna to get DTV."

If you've already purchased a DTV converter that doesn't have analog pass-through, you're not completely out of luck. You still may be able to get analog signals to your TV by using an antenna switch or 2-way splitter. Use a splitter if your TV has separate audio/video inputs. Just connect the antenna feed to the splitter, and run one cable from the splitter to the RF input on the TV and another from the splitter to the digital converter's RF input. Connect the converter's A/V output to the TV's A/V input.* You can watch the analog programs by changing channels using the TV's tuner. When you want to watch a digital channel, just switch to the video input.

For TVs that only have an antenna input connector (no separate video inputs), you'll need both an RF antenna splitter and an antenna A/B switch. The splitter should be connected between the antenna and converter box, with one cable connected to the DTV converter box's RF antenna input, and the other going to one of the inputs on the 2-way A/B switch (effectively bypassing the converter). Then run a cable from the converter box's RF output to the second input on the A/B switch. The A/B box's single output is then connected directly to the TV's RF (cable) antenna input. When the A/B switch is on the "digital" (A) side so it's receiving the converter box's signal, tune your TV to channel 3 or 4 to watch digital programs. When you click the switch to the "analog" (B) setting, you'll be able to view any available analog programs by changing channels on the TV. The downside is that you'll have to manually switch between the two inputs on the A/B switch every time you want to switch from an analog channel to a digital one.**

—James K. Willcox

* April 9, 2008 UPDATE: In a previous version of this post, we had inadvertently misplaced a line of text describing the correct procedure for using a converter box with analog pass through.—Ed.

** April 11, 2008 UPDATE: Additional information was added to help clarify how to use an A/B switch with a converter box.—Ed.
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