It's a VHF/UHF Active HDTV antenna. The large loop is the VHF element. The gray plastic looking part is the UHF element(s) and preamp. They were installed to pick up the local TV channels prior to the satellite companies starting to carry them. Often they used the same coax as the satellite dish so fewer runs of coax was needed. At the TV, there was a splitter that split off the lower frequency local signals from the higher frequency satellite signals. You had to switch off your satellite box to watch the local channels unless you were able to feed your TV using audio/video connections, which allowed you to simply change the TV's input from "antenna" to "Video".