Repeaters take in a message and 'repeat' it back out. Here are the common requirements for repeaters by band.
In order to re-transmit radio signals, repeaters utilize two different frequencies - one it “listens” on (receives - the input frequency) and one it “talks” on (transmits - the output frequency). As a result, your radio must be configured to work on two frequencies as well. This is generally not a problem as almost all VHF/UHF radios have this functionality.
On most radios, you’ll program in the receive frequency (transmit on the repeater), along with an offset value. This offset is the difference between the transmit and receive frequencies and may be positive or negative depending on the frequencies used. There are conventions for typical offsets for the different bands, but it does vary by region, etc.:
| Band | Frequencies | Offset |
|---|---|---|
| 10m | All | - 0.1 MHz |
| 6m | All | - 0.5 MHz |
| 2m | Below 147.00 MHz | - 0.6 MHz |
| 2m | Above 147.00 MHz | + 0.6 MHz |
| 1.25m | All | - 1.6 MHz |
| 70cm | Below 446.00 MHz | - 5.0 MHz |
| 70cm | Above 446.00 MHz | + 5.0 MHz |
Let’s say you are accessing a repeater that’s labeled as 145.250-. This means that the repeater has an output frequency of 145.250 and needs a negative offset. As a result, you’d program your radio with 145.250 MHz as the receive frequency and an offset of -0.6 MHz (giving you a transmit frequency of 144.65 MHz).
In addition to the offset, most repeaters also require a “tone” to be set in order to allow access. This is a simple frequency that your radio sends along with your voice transmission to trigger the repeater to “open up” and is commonly called a CTCSS or PL tone.
In addition, many repeaters also send a tone when they transmit to trigger your radio that it’s the repeater transmitting, but this is optional on your end - you’ll hear it either way.
