Doug Lung /
11.14.2008 02:10 PM
House Commerce Committee Probes DTV Transition

The House Committee on Energy and Commerce is closely examining lessons learned from September's Wilmington, N.C. analog shutdown.

Many viewers of Wilmington-area TV stations found that even with a DTV converter box, they were unable to receive some stations' programming when analog broadcasting was shut down in that market on Sept. 8.

NBC affiliate WECT moved its Channel 44 UHF DTV antenna closer to Wilmington to provide better coverage for its community of license, but was unable to deliver a satisfactory DTV signal over the rural areas previously served by its Channel 6 analog transmitter.

Except for a few markets where transmitting antennas are located on high mountains, it's impossible to cover the same area on UHF DTV as was covered on analog VHF with one antenna. People will watch a weak and noisy analog signal, but with DTV that's not an option. As the DTV signal drops below the noise limited threshold of the tuner the picture will fill with artifacts or disappear completely.

The problem is not limited to Wilmington. RF Report has discussed and linked to articles describing DTV reception difficulties several times.

"The Wilmington test identified many problems related to the DTV transition, including matters concerning rescanning analog-to-digital converter boxes, adjusting or acquiring antennas and changes in the areas where stations' signals are available," committee Chairman John Dingell, D-Mich., and Ed. Markey, D-Mass., chairman of the Telecommunications and Internet Subcommittee, said in letters to the major broadcast networks and affiliate organizations, NAB, the National Telecommunications and Information Administration and the FCC. They also asked each stakeholder what steps it will take to avoid similar problems on Feb. 17, 2009.

The letters to the broadcasters asked stations with DTV coverage areas smaller than their analog coverage areas what they intend to do to alert fringe analog area viewers to the post-transition signal loss situation. The letters also asked what steps were being taken to make viewers aware that antenna reorientation or new antennas will be needed to continue receiving TV.

The problem is most serious for low-band VHF stations (Channels 2 through 6) that are moving to UHF channels that depend on tower height, rather than mountain height, for coverage. In some markets, such as Washington, D.C., increased tower height may not be an option.

Some years ago in my RF Technology column, I addressed the channel congestion in the northeast United States. Squeezing all of the stations into the core spectrum (essentially those operating on channels 7-51) would increase interference, making it difficult for some large market stations to up their power to match their low-band VHF coverage without causing excessive interference to stations in adjacent markets.

While the House Commerce Committee letters did discuss antenna issues, they did not specifically refer to what I expect to be one of the biggest problems on Feb. 18—the loss of stations vacating UHF channels and returning to their former VHF analog channels. In many markets, including New York and Los Angeles, all DTV stations have been broadcasting on UHF and many viewers installing antennas for DTV reception have purchased UHF-only models.

The analog "soft shutdowns" being conducted in many markets will help viewers identify problems with DTV reception, only to the extent that the stations remain on their current channel or, at least, stay in the same band on Feb. 18.

However, the news isn't all bad for UHF DTV stations migrating to VHF channels. While viewers closer to the transmitter may lose indoor reception, more distant viewers with outdoor VHF antennas may find they can receive a reliable DTV signal from the station's VHF channel when they couldn't receive it on UHF.

While the FCC may have underestimated the impact of white space devices on cable and off-air TV reception, they have adopted rules for the use of distributed transmission systems. Although this may not be a practical solution to reach everyone predicted to lose TV reception on Feb. 18, it does provide a way to reach heavily populated areas outside DTV service contours.

There's one other bit of good news. On a trip to the East Coast in October, I found I was able to get UHF DTV reception in Hagerstown, Md., of some Washington, D.C., analog VHF stations, with far better picture quality (low-band VHF analog was barely watchable), even though I was outside the predicted noise-limited DTV coverage contour. Fortunately, interference was not a problem. For the checks I used an Artec T19ARD USB receiver, an Artec AN-2A amplified indoor "post card" antenna in a third-floor room and with an outdoor antenna and preamp 30 feet up in a residential neighborhood.



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