Doug Lung /
12.24.2008 12:00AM
FCC Maps Show Where DTV Coverage Doesn't Match Analog
One of the lessons learned in the Wilmington, N.C., analog shutdown was that digital coverage doesn't always replicate a stations' analog coverage, especially when the two transmitters are at different locations. As previously discussed in RF Report, Congress started an investigation into the problem and asked broadcasters to submit reports detailing any loss of analog coverage area post-transition. As most readers know, there are many ways to calculate coverage and the results won't match in most cases. The FCC conducted its own detailed study to answer the request from Congress. As you can imagine, the study is huge. The two zip files containing the reports and maps total about 175 MB!

To see how your TV viewing may be affected, see the FCC web page Map Book of All Full-Power Digital Stations Authorized by the FCC. On that page, you can download the entire report, look at coverage for the ABC, CBS, Fox, NBC and PBS stations for the entire U.S., or look at market specific maps. You may be disappointed, as I was, in the DTV versus analog coverage at your home. That's not to say there aren't improvements in coverage. Indeed, looking at the maps there are a lot of people in areas that are predicted to get DTV service that were not predicted to receive analog service.

Looking at the nationwide network coverage maps, it’s easy to identify stations with UHF analog channels and those with low VHF analog channels. The UHF analog stations usually have a green halo around them, indicating new coverage from the DTV signal. Low VHF stations, on the other hand, often have a yellow or orange halo around them, indicating the area where their analog viewers are not predicted to have DTV coverage.

In viewing these maps, keep in mind that they, like the ones on the TVFool Web site and antennaweb.org are based on the antenna data in the FCC database. As I've pointed out in my RF Technology column, this data is based on the horizontal plane azimuth pattern with the elevation pattern otherwise ignored in favor of a default pattern. In areas with mountaintop transmitter sites where mechanical beam tilt is used, such as Los Angeles, these patterns will not match reality. The results will be more accurate in “flat land” areas like Florida or areas with low mountains where stations are unlikely to use mechanical beam tilt on their antennas.

The recently passed rules allowing distributed transmission systems and the NPRM started this week for digital replacement translators provide some tools for matching digital and analog service areas.

Read more of Doug Lung's RF Report here.


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