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A repeater is a radio on a high place that hears weak signals and re-transmits them strong. It can't listen and talk on the same frequency at the same time - it would hear itself - so it uses two: an input it listens on and an output it transmits on. The distance between them is the offset.

By service

• GMRS: always +5.000 MHz. Output on 462.xxx, input on 467.xxx. No exceptions.
• 2 m ham: 600 kHz, plus or minus depending on where in the band the repeater sits.
• 70 cm ham: 5 MHz, usually plus, minus in some regions.
• 1.25 m: −1.6 MHz. 6 m: commonly −1 MHz or −500 kHz. 33 cm / 23 cm: varies, check the listing.

What your radio does

You tune the output (so you hear the repeater). You tell the radio the offset direction and amount. When you press PTT, it automatically shifts to the input, and shifts back when you release. That shift is called duplex operation; talking directly radio-to-radio on one frequency is simplex.

Listings on ChatterBack

A repeater page shows the output as the big number and the input underneath. Ham listings show the direction as a sign: 146.940−. GMRS listings just show the pair, because it's always +5.

If you can hear the repeater but it can't hear you, and the tone is right, flip the offset direction. That's the fix nine times out of ten.