What is a repeater?

A repeater is a bidirectional amplifier designed firstly to amplify the signals from the base station (relay) to the mobile and secondly to amplify the signals from the mobile towards the base station. Direction "base station to relay" is described as downlink (downlink in English), the other direction (mobile to relay broadcast) is called uplink (uplink in English). Uplink and downlink frequencies are generally differentiated and the difference between these two frequencies is called "duplex spacing".