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If you've ever tuned to a GMRS channel and heard nothing — even though others say the repeater is active — you're probably missing a CTCSS or DCS tone. These are privacy codes that act as a filter on your radio's squelch, so it only opens for transmissions that include the matching tone.
CTCSS (Continuous Tone-Coded Squelch System) sends a low-frequency tone (67.0–254.1 Hz) underneath your voice the entire time you transmit. It's below the audible range, so you won't hear it, but other radios can detect it. If their CTCSS is set to the same frequency, their squelch opens. If not, they stay silent.
DCS (Digital-Coded Squelch) works the same way but sends a continuous digital code instead of an analog tone. There are 104 standard DCS codes. DCS is more resistant to false opens from noise or interference than CTCSS.
Important: CTCSS/DCS is not encryption. Everyone on the frequency can still hear you if their squelch is open or they're using a different tone setting. It only controls whether your radio plays the audio — it doesn't make your transmission private.
Your radio has two tone settings per channel:
For repeaters, both TX and RX are usually the same tone. Check the repeater listing on our repeater directory for the specific tone — it's listed alongside the frequency and offset.
While any tone can be used, these are some of the most commonly seen on GMRS repeaters:
Different radio brands label CTCSS tones by number (e.g., Midland "Code 22" = 141.3 Hz). Use our CTCSS/DCS tone lookup tool to convert between brand codes and actual frequencies.