How do GMRS repeaters work

Understanding GMRS Repeater Pairs

GMRS (General Mobile Radio Service) repeaters work on pairs of frequencies that are 5.00 MHz apart. This means that there is a +5.000 MHz offset from the standard 50W GMRS frequencies, which are found on channels 15-22.

Frequency Offset and Repeater Output

The repeater outputs overlap with these GMRS frequencies, so anyone tuned into those channels will hear the repeater. This overlapping allows the repeater to capture signals from lower-power GMRS radios and re-transmit them at a higher power, extending the communication range significantly.

Preprogrammed Repeater Frequencies

One of the advantages of GMRS radios is that they typically come with repeater frequencies preprogrammed. This makes setting up communication via a repeater quite straightforward. The user just needs to add the appropriate TX (transmit) tone.

Dual Frequency Selection

In amateur radio (ham radio), you don’t just pick a single frequency; you pick two: one for listening and one for transmitting. Conventionally, these are spaced 5 MHz apart on the 70 cm band and 0.6 MHz apart on other bands. Many ham radios automatically apply these offsets.

Applying the Same Principle to GMRS

GMRS works in a similar way. When you use a GMRS radio on a repeater channel (15-22), the repeater transmits on the same frequency as simplex communication on that channel. However, your radio will switch to transmit at +5 MHz. This ensures that your transmission reaches the repeater, which then rebroadcasts it at a higher power.

For a detailed chart of GMRS channels and frequencies, you can refer to resources like Radio Reference or Buy Two Way Radios.

Conclusion

GMRS repeaters significantly enhance communication range by re-transmitting signals at higher power. With preprogrammed repeater frequencies and a straightforward setup process, GMRS radios offer a user-friendly solution for extended communication, especially useful in areas with large coverage needs.

By understanding the principles of frequency offset and dual frequency selection, you can effectively use GMRS repeaters to ensure clear and reliable communication.