By now you’ve probably seen the articles about the Centris study that found a “major glitch in the DTV transition.”
David Klein, executive vice president of Centris, cautioned that DTV coverage might not live up to other claims.
“We predict that digital TV signal coverage will be more limited than currently anticipated,” Klein said. “An issue that, until now, has been completely overlooked by the FCC and governing bodies, and could have serious – and costly - implications for millions of consumers.”
A Centris Press Release says, “With less than one year—and counting—until the DTV transition takes place, the potential gaps in digital coverage present a huge problem for the TV industry, and an equally large opportunity for cable, satellite and telecom video service providers as well as for manufacturers and distributors of ‘smart’ television antennas.”
Similar problems were identified as having emerged in the United Kingdom’s digital transition, with recognition that better “more sophisticated” antennas would be necessary for DTV reception.
While I have not seen the actual study, examination of information about the study available to the public and the press indicates the study was done using the Consumer Electronics Association’s www.antennaweb.org Web site, entering zip codes at five-mile intervals from the TV towers in a 60 to 75 mile radius “corresponding to the FCC-identified service contours.”
Centris warned that, “Alarmingly, the results showed there was little continuous coverage beyond 35 miles.”
If this doesn’t sound right, it appears the Centris study focused on small outdoor and indoor antennas, since it notes its surveys revealed “75 percent or more of the over-the-air households have only set-top antennas.” If the focus were on indoor antennas, then it would make sense. However, at distances past 35 minutes indoor analog reception is likely to be poor as well. I’m sure many readers’ experience with indoor antennas matches mine—you might be able to receive analog stations with very weak signals, but the noise and snow makes them unwatchable. The Centris statement “with so many sets potentially at risk of going dark, network, local and public television, advertisers and agencies will likely be adversely affected” seems alarmist.
I’ve received many reports from readers of reliable DTV reception 60 miles or more from the transmitter sites. Of course, these readers were using outdoor antennas, but in locations that far from the transmitter site most viewers of off-air analog TV will have outdoor antennas that will work just fine for DTV.
The study criticizes the FCC for using service contours that extend 60 to 75 miles for determining coverage. That is a misinterpretation of the FCC analysis, as the FCC uses the same Longley-Rice propagation model to determine coverage that the antennaweb.org site uses for point-to-point calculations. The population numbers the FCC listed in the 1998 DTV Table of Allotments are based on Longley-Rice. The one difference, which the Centris researchers may not have realized, is that when the FCC says a DTV station will provide 99.5 or 100 percent coverage, that coverage is referenced to the population able to receive the analog signal from the same station using the same Longley-Rice propagation model, with the signals levels reduced to reflect the increased sensitivity of DTV receivers and the time variability increased from 50 percent for analog to 90 percent for DTV to compensate for the cliff edge effect of DTV. While the FCC model is based on reception with an antenna 30 feet high, the same antenna height is used for the analog coverage analysis.
In information made available to the press, Centris says the FCC model does not take into account multipath interference. That is correct, but misleading. Any modern DTV receiver can handle multipath that would make an analog picture unwatchable. Some ATSC demodulators can even take advantage of the multipath to decode a DTV signal where any individual signal without multipath would be unwatchable. My experience with indoor reception in Washington, D.C., Philadelphia, New York and similar urban areas is that multipath improves indoor reception. A simple whip antenna, with no orientation required, allows many stations to be received with no line-of-sight to the tower when there are buildings to reflect signals into the window. Of course, strong signal levels are required for this to work, but that’s likely to be the case in urban areas where most indoor set-top antennas will be used.
The Centris study makes one important point. Antennas have been overlooked in the discussions about DTV converter boxes and DTV tuners. Outside strong signal areas (that 35-mile distance the study mentions) antenna selection will be important. In some cases an indoor preamplified antenna like the Terk HDTVa will be enough. In other, more distant locations, an outdoor antenna will be needed. Consumers receiving good analog pictures now should have little to worry about, but cable TV and satellite subscribers without good off-air analog reception in rural areas that think they can hook an indoor antenna to their NTIA-approved set-top box and get all the network signals will probably be disappointed.
The Association for Maximum Service Television (MSTV) criticized the Centris study. David Donovan, president of MSTV, said, “Consumers needing outdoor antennas for digital reception will need to use the same type of outdoor antenna they now use for analog reception. It is simply wrong to suggest that DTV service will not be available in areas outside of 30 miles from a DTV broadcast tower.”
Does DTV work beyond 35 miles of the transmitter site?
I’ll leave it to the RF Report readers to answer that question. If you are receiving DTV signals from more than 35 miles away, drop me an e-mail. If possible, let me know what type of antenna you are using and whether or not you have a clear view towards the tower sites, but don’t worry if you don’t have time to send the details. I’m especially interested if you are using an indoor antenna for reception over a path greater than 35 miles. What’s the maximum distance over which you can reliably receive DTV?
If RF Report readers respond, we should know next week whether DTV works beyond 35 miles in the real world.
