Datum Conversion in REC Broadcast Tools
Over the years, geographers have developed different methods of representing a precise location on the earth using geographic coordinates. In North America, the two commonly most used ones are:
- NAD27 - North American Datum 1927. All FCC broadcast related records (in CDBS in its predecessor BAPS) use this datum for representting geographic location.
- NAD83 - North American Datum 1983. This datum is used by the FCC in more modern applications such as the Wireless Telecommunications Bureau's Universal Licensing System (ULS) and the Antenna Structure Registration system. NAD83 is also used by most major online mapping services including Google Maps and Yahoo Geocoding, which are used by REC.
For determining distances between stations for purposes of 73.807 compliance, the FCC uses NAD27 at both locations. If a location is entered using NAD83, there may be a slight difference in the actual distance separation since two different datums are used in the comparison.
REC has developed a method of doing "best effort" datum conversion between NAD27 and NAD83.
If the NAD27 geographic coordinates are entered, those coordinates will be used by the channel search engine to determine distance seperations. NAD27 is also automatically assumed when the location entry is performed in myLPFM when using the [Exiting Tower] option and entering either a broadcast call sign or facility ID. When NAD27 coordinates are entered, REC will make a best effort to convert the coordinates to NAD83 for the purpose of rendering locations on Google Maps. NAD83 coordinates are also used for measuring distances to airports.
If the NAD83 geographic coordinates are entered, these coordinates will be used for rendering locations in Google Maps as well as other functions such as airport searches. If the NAD83 coordinates are used, REC will make a best effort to convert the coordinates to NAD27 for the channel search engine.
Please note that myLPFM defaults to NAD83 entry when the following entry methods are used:
- Search by community name.
- Search by ZIP code.
- Address entry (Yahoo geocoding).
- Search by Antenna Structure Registration Number (ASRN).
- Clicking a location using Wide Area Search or Tower Search.
REC's conversion of NAD27 and NAD83 is not precision but is usually accurate to under 1 second. The FCC's tolerance on locations is one second. In other words, the geographic location that you enter on your Form 318 must be within 1 second latitude and longitude of your actual antenna location.
For the purpose of filing applications, if you only have the NAD83 coordinates, you can convert those to the precision NAD27 coordinates by visiting NOAA's NADCON website.
NAD27 and NAD83 are normally used only within the continental US. For Hawaii, Alaska, Puerto Rico and the Virgin Islands, REC uses NAD conversion to and from NAD83 which is considered as standard for those areas. Conversion services are not available at all for Guam, American Samoa or the CNMI.
REC is not liable for consequential damages caused by our conversions between NAD27 and NAD83 and vice versa.