Essentially a repeater is a radio that have been installed on a high point (Hill) that receives your transmission and re transmits your signal. Because the repeater is on a hill, it tends to increase your coverage and allows your transmission to be received by a far greater distance.

In reality a repeater actually is 2 radios, 1 radio to receive the incoming transmission and 1 radio to re-broadcast the transmission.

ALL REPEATERS must be carefully engineered and require full RSM licensing. These are engineered / licensed on a site by site situation.