When a wireless carrier selects a candidate cell site it will usually conduct a 'drive test' to determine actual coverage. The drive test consists of elevating an antenna to a predetermined height. Inside the truck is a portable PCS transmitter powering the antenna. In a separate vehicle (call it a 'rover') the carrier will drive the streets around the test site out to a predetermined distance from the site. The received signal level and GPS location information are stored in a portable computer inside the rover.
After the test is concluded, the received signal strength and location information are plotted on a street map. That map then serves to guide the RF engineer to select a final candidate site, and to design the antenna system to cover the desired area without causing unreasonable interference to other cell sites on the same network.
Attached to the left of the antenna (and blowing in the breeze) is a measuring tape used to determine the height of the antenna.