Repeaters do just that- they REPEAT a signal recieved and RE-TRANSMIT (or repeat) a signal. IF this repeater is on a hill top, mountain top or a tall building, they are able to EXTEND the coverage of a mobile, handheld, or base (control station) radio.

To DO THIS, we have to use TWO frequencies: one that transmits to the "repeater" where it is processed, and then "REPEATED" out on another frequency. In the case of GMRS there are a few pairs of transmit and recieve frequencies available to use. Let's pick one pair for an example. 462.650/467.650 (Mhz).

In our example above, the REPEATER recieve frequency is 467.650 Mhz. When it recieves this frequency, it IMMEDIATLEY processes it and RE-TRANSMITS or repeats or transmits this audio out on the other frequency in the pair on 462.650 Mhz. MOST repeaters have high quality recievers that are able to "hear" low powered mobile, handheld, and base radio signals. They then retransmit at a higher power in an omni-directional pattern antenna pattern, to be heard by many others, sometimes in a large geographical area.

WORD OF CAUTION: Often when discussing "transmit" and "receive" folks confuse these two terms as they apply to REPEATERS and radio units in the field. They are opposite!
EXAMPLE (using the frequency pairs above):
Mobiles and handhelds TRANSMIT on 467.650 Mhz and RECIEVE on 462.650 Mhz
Repeaters TRANSMIT on 462.650 and RECIEVE on 467.650

(I'll try and post a few BASIC topics to help new GMRS users understand "how things work". I'm NO expert, but hoping to help!
Please feel free to post additional info you think might help!!)
Dave WRQU806