In amateur radio, a repeater utilizes a frequency offset to avoid interference between its transmitted and received signals. For a repeater operating on a designated output frequency such as 145.150 MHz, a standard input frequency is established. This input frequency is shifted by a specific amount, termed the offset, to allow radio operators to transmit to the repeater on one frequency while the repeater simultaneously retransmits on another. The offset is typically plus or minus 600 kHz in the 2-meter band. For 145.150 MHz, the standard offset is -600 kHz.
Employing an offset allows for full-duplex operation, where simultaneous transmission and reception occur. This is crucial for the functionality of a repeater, enabling it to receive weak signals from distant or low-powered stations and retransmit them at a higher power level, thereby extending communication range. Historically, coordinated frequency planning and standardization of these offsets facilitated efficient spectrum use and minimized interference between repeaters and other radio services.
