When you file your online radio application with the FCC, you will be asked to fill in the exact latitude, longitude and elevation (in meters) of your proposed antenna. It’s easier than you think, and doesn’t require any specialized equipment. We’ll show you how get located with Google Maps and the USGS, Google Earth, a GPS or cellphone, and our very own RFree software.
But Which Coordinate System?
Over time, our knowledge of the shape of our planet, and our ability to measure locations and distances has improved. There are three different systems (references) for latitude and longitude, called geodetic datums. We care about three of them, NAD27 (North American Datum of 1927) and NAD83 which is often used interchangeably with WGS84. Luckily, we don’t have to worry about this very often these days since most everything is using NAD83/WGS84 now.
But… The FCC has required NAD27 for most of its existence, and only in the first part of the 2020’s started accepting NAD83 for (almost!!!) all broadcast applications. Forms in the FCC’s older CDBS online system use NAD27. Older paper maps, like USGS topographic maps, used NAD27, and some may remain today. If you ever need to convert, the FCC offers suggestions.
Google Maps and The USGS
(For the google methods to work, we need to know what reference datum Google uses, which seems to be WGS84 which for our purposes is as good as NAD83.)
- Starting at maps.google.com, navigate to your location and zoom in
- Switch to the satellite view and zoom in some more if needed
- Place your mouse at the desired location for your antenna, right-click and select What’s here? from the menu. –OR– left-click on the desired location.
- The pop-up at the bottom of the screen shows the coordinates of where you clicked, but they are not on the degrees-minutes-seconds form requested by FCC forms. Click on them.
- Now the coordinates are also shown in the location search box looking like this:
39.948273, -75.218727and a bit below that in degrees-minutes-seconds format like this:
- Save these numbers, in both formats! The FCC will need the latter format, and the USGS will need the former format!
But How High is It? What’s the Elevation.
Your FCC application requests the elevation at the location of your antenna. Google Earth is one way to determine the elevation (see the next section) and here’s how to get it from the USGS (U.S. Geological Survey).
- Go to the USGS Elevation Point Query Service
- Enter your LONGITUDE (like -75.218637) into the “X:” box, and do not forget the minus sign,
- Your LATITUDE from Google goes into the “Y:” box
- Select Units: Meters and Output: JSON
- Click [Get Elevation] (it can take a minute)
- You can pick out the elevation from JSON text on the next page. Look for the number after “value” like this….”value”:”30.994913101“….
This uses the downloaded Google Earth rather than the online version, which probably works just as well but we haven’t checked it out yet.
- Start Google Earth and navigate to where you want to put your antenna. You should zoom in pretty close so that you can be accurate to a foot or two.
- Click on the antenna spot
- Select the “push pin” to add a placemark.
- Copy the coordinates from the pop-up, which are already in the degrees-minutes-seconds form needed by the FCC.
- Before you close the pop-up, and with your mouse over the pop-up — not the map — note the height which is shown after the word “elev” on the bottom line of the map, for example “… elev 39 m eye alt …”
GPS or Cell Phone
This seems like the obvious method to find coordinates, but it can be less accurate than the methods above unless you use the same techniques as surveyors, which is beyond the scope of this document. GPS ok-ish for latitude and longitude, but the altitude is often pretty far off, and the US Department of Defense controls the latitude/longitude accuracy and can make it worse any time.
Most GPS units should display the WGS84 datum, so that part is fine. But be warned that some GPS units give latitude and longitude in an unusual format, like 36 11.234, -76 33.999 (degrees followed by minutes and decimal fraction of a minute), which will need to be converted to degrees, minutes, and seconds for FCC purposes.
RFree, Prometheus’ Radio-engineering Software
Using RFree, you put a marker on a map at your antenna location, and RFree determines the coordinates and elevation automatically, and provides coordinates in the different formats required by other systems and software. RFree’s primary purpose is to know which locations and frequencies satisfy FCC requirements, so you can be confident filing your FCC application.
A word about height
If you have a choice, put your antenna as much higher than the surroundings as possible. While it’s not optimal, perfectly adequate coverage can be had from a twenty or thirty foot antenna located on a residential rooftop, all other things being equal. Depending on the antenna you choose, it can look less obtrusive than even a standard TV reception aerial.
You can find out much more in our Transmission Toolkit.
A word about location
Also keep in mind: While it is best and cheapest to have your studio and transmitter at the same site, nothing needs to be at the transmitter site except for the transmitter, electric power, the antenna, and some sort of STL (studio-to-transmitter link) for audio from your studio.
Check out Sound Around Town for more.