SBE: Drop NAD27 From Broadcast Databases

The Society of Broadcast Engineers is calling upon the FCC to drop its use of NAD27 coordinates in favor of the more accurate NAD83 datum.

Antenna structure registrations and microwave licenses use the NAD83 datum to specify location, as do most other FCC licenses. GPS receivers and mapping software usually default to the WGS84 datum, which is for all practical purposes the same as NAD83. Broadcast licenses, whether issued to AM stations 50 years ago or to DTV stations being built today are based on the older NAD27 datum.

This matters because different datums, which are used to map coordinates to the Earth’s surface, affect how coordinates map to specific locations. The datums allow locations on the Earth’s surface to be mapped into latitude and longitude. Because the Earth isn’t a sphere, this isn’t trivial. The newer datums, such as NAD83 and WGS84, are based on more accurate mathematical descriptions of the Earth’s shape. Use the wrong datum, and your transmitter site at the point of a narrow mountain peak could end up significantly lower. Interference and coverage calculations based on coordinates using the wrong datum could dramatically affect protected coverage areas and population.

One reason broadcast licenses still use NAD27 is that was the latest datum when most stations were originally licensed. While software is available to do the conversion between datums, it isn’t always used correctly. When licensing DTV facilities, I saw cases where stations licensed transmitter locations were not where the stations thought they where! Why not convert broadcast licenses to NAD83 coordinates, so they match current GPS and mapping software defaults and other FCC licenses? Now that data on FCC licenses is stored electronically, it would only take a few lines of code to link to a program that would do the datum conversion.

The Society of Broadcast Engineers (SBE) decided there was no reason for broadcast licenses to continue to use NAD27 coordinates. In a Petition for Rulemaking filed last week, the SBE asked the FCC to convert the Media Bureau’s Consolidated Data Base System (CDBS) to North American Datum 1983 (NAD83).

In the Petition, SBE cites several FCC actions supporting the use of NAD83. The Petition states, “In light of the fifteen years that have passed since the FAA converted to NAD83, and in light of the eight years that have passed since WTB converted to NAD83, SBE submits that the Media Bureau (MB) is past-due to convert the CDBS to NAD83. SBE further notes that the International Bureau uses only NAD83 coordinates, as does the Office of Engineering & Technology. The continued use of NAD27 coordinates by the Media Bureau causes nothing but confusion (i.e., ‘Are the provided coordinates NAD27 or NAD83?’) to persons filing with both the Media Bureau and the Wireless Telecommunication Bureau (e.g., with the Media Bureau for broadcast stations, but with the Wireless Telecommunications Bureau for Broadcast Auxiliary Service (BAS) stations and antenna structure registrations). To circumvent this confusion, the Media Bureau should embrace NAD83 and convert all existing NAD27 coordinates in the Media Bureau’s CDBS.”

SBE notes there is no need to re-issue all broadcast station licenses with NAD83 coordinates, stating, “it would be sufficient to simply reflect NAD83 coordinates on all newly-issued authorizations, with the datum clearly indicated.” It concludes, “The Media Bureau should immediately convert the CDBS to NAD83. ... Such conversion will simplify Media Bureau filings and reduce coordinate conversion errors that must now be made in connection with Media Bureau filings.”