Repeater Offsets and Splits

Every GMRS repeater uses two frequencies: one to receive your signal (the input) and one to retransmit it (the output). The difference between these two frequencies is called the offset. Understanding offsets is essential for programming repeaters into your radio.

Why two frequencies?

A repeater can't transmit and receive on the same frequency simultaneously - its own powerful transmission would drown out incoming signals. By listening on one frequency and transmitting on another, the repeater can receive and retransmit at the same time, giving you real-time communication through it.

The standard GMRS offset: +5 MHz

On GMRS, the input frequency is always 5 MHz above the output frequency. When you program a repeater, you enter the output frequency (what you listen to) and set your radio's offset to +5 MHz. Your radio then automatically transmits 5 MHz higher. The 5 MHz split was chosen by the FCC to provide enough frequency separation for a duplexer to achieve adequate isolation between the transmit and receive paths - with only a 5 MHz split, duplexers must be very high-quality. See Duplexers for more on that challenge.

GMRS repeater frequency pairs

Channel	Output (Listen)	Input (Transmit)	Offset
15R	462.5500 MHz	467.5500 MHz	+5 MHz
16R	462.5750 MHz	467.5750 MHz	+5 MHz
17R	462.6000 MHz	467.6000 MHz	+5 MHz
18R	462.6250 MHz	467.6250 MHz	+5 MHz
19R	462.6500 MHz	467.6500 MHz	+5 MHz
20R	462.6750 MHz	467.6750 MHz	+5 MHz
21R	462.7000 MHz	467.7000 MHz	+5 MHz
22R	462.7250 MHz	467.7250 MHz	+5 MHz

How your radio handles the offset

Most GMRS radios handle offsets one of two ways. Some have GMRS repeater channels pre-programmed from the factory - selecting "channel 15R" automatically sets the correct output frequency, offset, and direction without any manual configuration. Others require you to program each memory channel manually, entering the output frequency, duplex direction (+), and offset amount (5.000 MHz). When you key up on a properly programmed repeater channel, the radio automatically shifts its transmit frequency to the input without you doing anything. You always hear on the output; the radio does the math for transmitting.

How to program the offset

1. Enter the output frequency (e.g., 462.5500 for channel 15R)
2. Set the duplex mode to positive (+)
3. Set the offset to 5.000 MHz
4. Program the required CTCSS/DCS tone (see CTCSS & DCS Tones)
5. Save to a memory channel

In CHIRP, these fields are labeled "Frequency" (output), "Duplex" (+), "Offset" (5.000000), and "Tone" / "rToneFreq." See Programming with CHIRP for a walkthrough.

Common programming mistakes

• Wrong duplex direction: setting the offset to negative (-) instead of positive (+) causes your radio to transmit 5 MHz below the output frequency - outside the GMRS band entirely. The repeater will never hear you
• No offset at all (simplex mode): if duplex is set to "off" or "simplex," your radio transmits on the same frequency it's listening to. That's the output frequency - not the input the repeater is listening on. You'll never trigger the repeater
• Wrong offset amount: entering 0.600 MHz instead of 5.000 MHz (a common mistake when people confuse GMRS with VHF repeater conventions) sends your transmission to the wrong frequency
• Missing CTCSS tone: most repeaters require a tone to open the squelch. Even with a perfectly programmed offset, you'll hear the repeater but it won't key up without the correct tone
• Confusing input and output: entering the input frequency as the channel frequency and forgetting to set the offset results in monitoring the input (where nobody is listening) instead of the output

Simplex vs repeater channels

Channels 15-22 can be used in both simplex mode (direct radio-to-radio on a single frequency) and repeater mode (with the +5 MHz offset). When you see "15R" or "channel 15 repeater," it means the repeater pair. When you see just "channel 15," it typically means simplex on 462.5500. Make sure your radio is set to the correct mode for how you intend to use the channel.