It is known as radio repeating. Radio stations use them to boost their signals into new territories. Cell towers too. Radio repeating: "[It's]...a combination

It is known as radio repeating. Radio stations use them to boost their signals into new territories. Cell towers too. Radio repeating: "[It's]...a combination of a radio receiver and a radio transmitter that receives a signal and retransmits it, so that two-way radio signals can cover longer distances. A repeater sited at a high elevation can allow two mobile stations, otherwise out of line-of-sight propagation range of each other, to communicate. Repeaters are found in professional, commercial, and government mobile radio systems and also in amateur radio. ..."