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When two radios communicate directly with each other, this is known as Simplex. To achieve greater range, a radio repeater is often utilized. Each portable radio communicates with the repeater and the repeater rebroadcasts the signal for the other portable.
A Repeater is a device which will receive a signal on one frequency and re-transmits the signal with increased strength on another frequency simultaneously in a two-way radio communication. Transmissions are received from portable two way radios by the repeater and then are broadcast at a much higher wattage on a different frequency.
Repeater is nothing new to amateur radio (HAM) operators and they all know that it uses different transmitting and receiving frequencies. Setting up the radio to repeater-mode is no big deal but with FRS radios repeater-mode is not implemented at all.
In general, repeater systems are usually located in places of high elevation (on tall towers, on top of mountains or tall buildings) and are equipped with large and efficient antennas, extremely low loss feedlines, and a transmitter and receiver that is very durable, rated for continuous duty, and built to be as immune as possible to interference.
For a radio to be repeater capable, it must support having different transmit and receive frequencies for the same channel. Frequencies used for repeater communications are typically not standard built-in frequencies, so repeater capable radios are usually “fully programmable”.
As we all know, longer the distance a signal must travel, weaker it gets.
This phenomenon is called signal attenuation. Repeaters are very essential since it boosts the signal power and reduces signal attenuation drastically during radio communication.
A repeater “gets out” your signal and receives the station you are talking to with a far greater range and coverage area! Repeater systems are used to “transfer” your transmitted and received signals to much higher elevations electronically using large, very efficient antennas, low loss feedlines and a transmitter and receiver that is rated for heavy or continuous duty.
In order to listen and transmit at the same time, repeaters use two different frequencies. One is for transmitting frequency and another for receiving frequency. This is referred to as offset. Without having an offset between the transmit signal and the receive signal frequency, the repeater would simply hear itself when it was transmitting on the same frequency it was listening on!
Repeaters are used in cellular communication to handle the hand-off concept, when the user moves out of one cell to another cell. This helps the user to receive a proper signal by making sure that the signal level does not drop.
Radio repeaters are allowed on Amateur (HAM), GMRS (General Mobile Radio Service), and Business Band. Radio repeaters are not allowed on CB (Citizens Band), FRS (Family Radio Service), or MURS (Multi-Use Radio Service).