CTCSS (Continuous Tone-Coded Squelch System) Codes
*Some radios use 69.4 Hz instead, which better fits the harmonic sequence, and this tone is often omitted as a choice.
CTCSS codes are functions that reject undesired signals on your channel. You will hear a call only when you receive a signal that contains a matching CTCSS tone or DCS code. If a call containing a different tone or code is received, squelch will not open and you will not hear the call. Likewise, when transmitting using CTCSS or DCS, the receiving station must have a matching tone or code to hear your call.Be aware that other parties can still hear your calls if they set up their transceiver with the same tone or code.