Originally, ITFS stations were licensed to transmit only video signals from a single transmission site (typically a tower or building rooftop) to specific receive site locations. New stations were permitted to be licensed on the same channels or adjacent channels if they did not cause interference to the reception of an ITFS signal at any other station’s receive sites.
Under EBS rules adopted in 2005, stations were transitioned to geographic area licenses, with each station's Geographic Service Area (GSA) defined as a 35 mile radius from the license’s reference point (typically the old video transmission site). A geographic license authorizes operation of one or more transmitters at any location within the GSA, and a licensee is generally free to add new transmitters, relocate or remove transmitters, or change technical operating parameters of transmitters without FCC approval, as long as transmitters comply with technical requirements intended to protect nearby EBS stations from interference.
Many ITFS stations were originally licensed at transmitter sites that were less than 70 miles from other ITFS stations operating on the same channels, the 35-mile radius GSA circles established in 2005 would have resulted in overlapping GSAs. To avoid that problem, the FCC created exclusive GSAs by splitting the overlap areas between or among the overlapping stations using a process often referred to as “splitting the football.”
A list of the Views On Learning Geographic Service Areas is available here.