Repeaters help with the problem of line of sight in conventional communications. If two way radios want to communicate with a hilltop in the way, then there is no line of sight. One way to overcome this is placing a repeater at the top of the hill. One radio communicates up to the repeater, this is called uplink, and then the repeater repeats that transmission down to the radio on the other side of the hill, this is called downlink.
However, repeaters are used even when there are no hills in the way as they are excellent for extending range. A repeater is an extremely powerful radio. Portable radios work in five watts, mobile radios work in 25 watts or more, and repeaters are even more powerful radios in the 50 to 100 watt range.
Commercial enterprises that operate across vast or congested regions, emergency services, public transportation, and amateur radio hobbyists employ radio repeater networks.
In addition, they are often utilized in big locations, such as a warehouse or hotel, when the structure of the building makes it difficult to cover. Several specific applications for radio repeaters are:
1, Radio repeaters increase coverage in systems that use frequencies that propagate in a line-of-sight manner. Without them, the range of these systems is limited due to the curvature of the Earth and the blocking impact of terrain or tall structures.
2, Radio repeaters may also translate one set of radio frequencies to another, allowing two distinct public service organizations to communicate with one another (say, police and fire services of a city or neighboring police departments).
3, They may also have connections to the public switched telephone network or a satellite network (BGAN, INMARSAT, MSAT) as a backup route from the source to the destination.