The Answer

The Global Positioning System is a system using small consumer electronics units to determine your exact location. They do this using signals from military satellites. Basic units range from $100 to $500, depending on their accuracy and their features. Some come with interesting mapping features and CD databases of maps that can be loaded on to the unit from a PC. Differential GPS units use a supplementary signal from a network of coast guard buoys that allow even greater accuracy.

Simple GPS units are generally available off the shelf at large chain department stores, sporting goods outlets and electronics stores. With some of these, you can add a special cable and antenna which will make it into a more accurate differntial GPS unit. The antenna and cable is usually only available through boating supply stores and mail order. Some applicants have gone out and bought a GPS unit from a monster chain store, used it to get the co-ordinates for their site, and returned it the next day for their money backSÿ"I didn't like the color, etcSÿ"

The FCC website says that a regular GPS unit is not accurate enough for radio station allocations. Handheld GPS units are usually accurate to two or three seconds, The FCC wants the co-ordinates that you submit to them to be accurate to the nearest second. A second of latitude or longitude averages about 20 meters in the United States. The FCC says is that you should use a differential GPS, but those don't work unless you are within 100 miles or so of a coast guard station. I have a differential antenna that hooks into mine, but it only works in some regions.

The FCC continues to use the NAD 27 set of maps for its allocation studies. GPS units use the somewhat more recently revised NAD 83 maps. If you use a GPS, make sure that it is using NAD 83 co-ordinates. Then go to this website: www.fcc.gov/mmb/asd and click on the red box on the left side that says NAD 27 to NAD 83 (depending on your browser , you may have to scroll down to see this button). Convert the nad 83 to nad 27 co-ordinates so that the information is compatible with the FCC database. You could also look at your town hall surveying maps. Your local highway department often has extremely accurate maps at a scale that is useful for this work.

You should strive for accuracy in what you submit to the FCC. Realistically speaking, probably no one will ever know that it is off by a few seconds here or there- unless a spiteful commercial station sends an engineer out to check the site. While this is very unlikely, any inaccuracy on your part could be the basis of a Petition to Deny your application. It is unlikely that the petition to deny would be successful based on a few seconds inaccuracy, but it might end up having to be investigated and could hold your application up for many months. On the other hand, using a GPS for altitude is a more serious problem. Your altitude must be accurate to the nearest meter, and no standard GPS can do this. You should use an accurate topographic map to determine your altitude. A library or town hall is best for this, but you can also see them on line at www.topozone.com