A repeater is a device that receives a radio signal at a certain frequency and transmits it to another. Repeater comes from the Latin word translator, which translates as "carrier". In amateur jargon, the repeater is called the repeater.
An active repeater is a transmitting / receiving station that receives, amplifies and transmits further a radio signal. A passive repeater is a flat reflector, a communication satellite, a mirror antenna, a belt of needles, etc., which scatters or reflects radio waves. Repeater has the form of a bi-directional amplifier. Using a directional external antenna, the amplifier receives a radio signal from the base station and, amplifying, sends the signal to the subscriber. An antenna directed toward the base station is called a pre-normal. An antenna that operates in the direction of the subscriber station is called a service one.

Mobile telephone systems are divided according to their method of building into ordinary systems and using a repeater. In conventional systems, a direct connection is established between subscribers on one particular channel. Repeaters have been used for over 50 years, helping to receive and transmit radio signals in areas that are difficult to reach.

Repeaters are used in office and amateur communications. Service repeaters operate in the HF and VHF bands, and amateur repeaters operate in the range of 145 MHz. The power of the amateur transponder is typically 100 watts.

Repeaters increase the service area and coverage of wireless networks. They improve the performance of mobile phones in "dead" and hard-to-reach areas, such as underground garages, exhibition halls and other objects located at a sufficiently remote distance. When the subscribers are talking on a mobile phone, they switch to the use of frequency channels, and thus the radius of the service area decreases. The base station of the network transmits an insufficient signal level; as a result, places are formed where communication is either absent or extremely unstable. Generally, the barrier for radio signals is shading of tall buildings or uneven terrain. Inside the premises, walls and ceilings make the signal weaker or absorb it altogether. A repeater can solve many problems by receiving and transmitting radio signals.

In fact, the repeater is a kind of antenna amplifier, it is called an amplifier for a cell phone. The difference between the repeater and the antenna amplifier is that the amplifier is connected to the telephone via cable, and the repeater via radio. In the operating mode, external directional antennas and internal antennas are connected to the reception and transmission of signals. External antennas are mounted on walls and roofs of buildings, and internal directional antennas are installed inside buildings. The antennas that are located in the building relay radio signals from mobile phones, thereby creating a zone in which stable communication is maintained. Repeater provides multiple users simultaneously. The repeater operates in duplex mode, in which you can amplify and transmit signals from the first to the second line, and vice versa.

Repeaters are installed not only on land, but also on watercraft. They enable the crew of the ship to use mobile communications not only in seaports , but also throughout the coastal area.