Designed to specifically monitor all modes of electronic transmissons - Electronic Intelligence (Elint) gathering.
Anything that produces any type of RF transmissions that can be captured....that is a lot of stuff - TV, CV radio, WiFi, military radio, cell phones, baby crib monitors - anything that is broadcast over the airwaves.
Rumor that a rombic antenna (huge ((acres of land)), diamond shape, highly directional) set up in Minnesota was listening to ground comm (hand held to hand held and hand held to base) in GW I.
No proof to give, but I am a licensed operator and understand the concept completely. Very much possible.
Found this - is this what it would look like?