A repeater receives a signal on one frequency and simultaneously retransmits (repeats) it on another frequency. The frequency it receives on is called the input frequency, and the frequency it transmits on is called the output frequency.
Sometime we may see the repeater downlink frequency and uplink frequency, what are they?
As usual, we say a repeater frequency is downlink frequency, it is repeater's output frequency. The uplink frequency is repeater's input frequency. The offset is uplink frequency minus downlink frequency.
For example, we say a repeater frequency is 439.9800, the offset is -5.0Mhz.
We can know that the repeater's downlink/output frequency is 439.9800. The uplink/input frequency = downlink frequency plus offset = 439.9800+(-5.0) = 434.9800Mhz.
Repeater frequency = Output frequency = Downlink frequency
Input frequency = Uplink frequency
Offset = Input frequency - Downlink frequency
After we know the repeater frequency, now we can learn the relationship between radio frequency and repeater frequency.
If you want to use the repeater, your radio must set the right frequency.
Your radio receive frequency is repeater output frequency. Your radio transmit frequency is repeater receive frequency.
For example, Repeater frequency is 439.9800MHz, the offset is -5.0MHz. How to set the radio?
Radio receive frequency is 439.9800Mhz, radio transmit frequency is 439.9800-5.0=434.9800Mhz.