Full Duplex Operation
A repeater is an automatic radio-relay station, usually located on a mountain top, tall building, or radio tower. It allows communication between two or more bases, mobile or portable stations that are unable to communicate directly with each other due to distance or obstructions between them.
The repeater receives on one radio frequency (the "input" frequency), demodulates the signal, and simultaneously re-transmits the information on its "output" frequency. All stations using the repeater transmit on the repeater's input frequency and receive on its output frequency. Since the repeater is usually located at an elevation higher than the other radios using it, their range is greatly extended.
Because the transmitter and receiver are on at the same time, isolation must exist to keep the repeater's own transmitter from degrading the repeater receiver. If the repeater transmitter and receiver are not isolated well, the repeater's own transmitter desensitizes the repeater receiver. The problem is similar to being at a rock concert and not being able to hear the weak signal of a conversation over the much stronger signal of the band.
In general, isolating the receiver from the transmitter is made easier by maximizing, as much as possible, the separation between input and output frequencies.
Read more about this topic: Radio Repeater
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