The Association of Maximum Service Television (MSTV) commissioned a study by BIA Financial Network to analyze how DTV coverage is affected by DTV stations' current facilities and how some station's "lower power" operation could impact the DTV transition. When the study was conducted in October, 52.6 percent of the operational DTV facilities were operating pursuant to a Special Temporary Authorization (STA), many at lower power levels than authorized in the stations' construction permit or application. However, even at the current power levels, over 70 million households are reached by six or more over-the-air DTV signals, with existing DTV facilities reaching 92.7 percent of their replication area populations.
In the study, coverage for existing facilities is based on the noise-limited threshold determined using Longley-Rice and the FCC Bulletin FCC OET-69 parameters, the same method the FCC used to determine the DTV replication population used by the FCC in the allocation table.
According to the study, 517 stations are operating pursuant to an STA. This number does not agree with the number I extracted from the FCC TV Engineering Database, which lists over 800 STAs. This difference could be caused by confusion over the FCC's use of seven different descriptors for STA operation (BDSTA, BDTA, BMDSTA, DBSTA, DSTA, DTV, and STA) in the CDBS TV_dom_status field and possible duplication of some records. It is possible the study's 517 number did not include educational/non-commercial stations or my number includes stations shown in the CDBS as having an STA that are not on the air.
The study looked at coverage based on the percent of replication for the 517 stations identified as operating under an STA. Of the group, 97 (18.8 percent) are serving over 100 percent of their replication population and approximately 60 percent of the stations are providing coverage to 70 percent or more of their replication population. The average percent of replication population covered was over 90 percent in markets 1-75, over 84 percent in markets 76 to 125 and 72 percent in markets 151 and smaller. Markets ranked 126-150 had 59 percent of replication population covered.
These percentages do not consider that some stations have many more viewers than other stations. When this is considered, the study found over 80 percent of the viewing is to local stations that have operational DTV facilities. If New York City were removed from the list, this number would increase.
The BIA study concluded, "Based on the data presented, the number of stations operating at significantly lower power constitutes only a small group of operational DTV facilities. Even stations operating pursuant to an STA are providing sufficient signal strength to cover most of their replicated population coverage area. Many of the stations, even in the smaller markets, are reaching over three-quarters of their existing populations. Given the reach of many of the DTV facilities and the fact that the most popular stations are reaching their replication areas, one can only conclude that the viewing public has many choices of DTV stations to select. Clearly, local over-the-air television stations have invested in and continue to operate enough DTV facilities to 'jump start' the digital transition."
I had some concerns about the study and discussed them recently with MSTV President Dave Donovan. My main concern was that the study was based on the FCC noise-limited threshold and OET-69 Longley-Rice coverage, not the 7-dB higher FCC "city grade" signal level or the even higher signal levels many studies have found are necessary for practical DTV reception, particularly when indoor antennas are used. As I pointed out in my RF Technology column in TV Technology earlier this year, many, if not all, of the DTV receivers currently being sold do not meet the parameters used in the planning factors that are the basis of FCC coverage predictions. It is also well-known that Longley-Rice, as used in OET-69, over-predicts signal levels over most unobstructed paths. None of this invalidates the premise of the study, which compares current coverage to the coverage the FCC calculated in the DTV allocation table. With the possible exception of the use of the DTV "City Grade" signal level, there is no other widely accepted method for determining DTV coverage. While current DTV receiver performance can be estimated, the wide variations in performance make it difficult to specify what new planning factors should be used. Should the best DTV receivers be used, since they represent what most consumers will be buying, or should older receivers be included because they represent the installed base?
David agreed to look into the possibility of repeating the study, using the DTV "City Grade" levels rather than the noise-limited thresholds for both the allocated and existing conditions. I pointed out that this would understate actual DTV coverage if the default FCC OET-69 UHF elevation pattern were used. Most lower-power DTV stations are using low-gain antennas which, in some cases, can put more effective radiated power near the transmitter site than high-power stations using high-gain antennas that focus most of the energy closer to the horizon. I've heard of at least two cases in different markets where the signal strengths in the nearby population center from stations operating with lower-power and low-gain antennas was higher than the signal strengths from some stations operating at much higher power with high-gain, more directional antennas. In these cases, even if higher-signal levels were required to show coverage, most of the population would be able to receive even lower-power stations.
My own quick analysis of DTV power levels, based on data extracted from the FCC TV Engineering Data for Nov. 1, 2003 (download the spreadsheet from www.xmtr.com/fcc/dt031101.zip), indicates the FCC has granted 762 STAs (excluding file prefix BMDSTA) for UHF DTV stations. Of these, 511 (67 percent) of the STAs are for power levels of less than 50 kW and 174 (34 percent) are for power levels over 100 kW. Sixty-two stations (including those with the BMDSTA file prefix excluded earlier) have or are requesting STA modifications for operation at power levels equal to or greater than 500 kW. The database shows 409 UHF DTV stations with a tv_dom_status of "LIC" (not under STA) and of these, 101 (24.7 percent) have a power level less than 100 kW, meaning 75.3 percent are over 100 kW. Seventy-five stations are shown with power levels at the FCC maximum of 1,000 kW.
To learn more, read the complete study, Reaching the Audience: An Analysis of Digital Broadcast Power and Coverage.
