Radio Basics: CTCSS

CTCSS (Continuous Tone-Coded Squelch System) is one type of in-band signaling designed to reduce annoyance of listening to other users who may be using the same frequency.

CTCSS works by adding a sub audible tone to voice transmissions. Users can typically select a tone between 67 Hz and 255 Hz.

Once a tone is selected the radio will only receive transmissions that also carry that tone.—CTCSS DOES NOT PROVIDE SECURITY— Use of CTCSS will not prevent others from receiving your traffic, it only prevents you from receiving unwanted signals.

To secure communications one need to employ scrambling* (low level privacy) or Digital mode encryption (high level security). We recommend the adoption of AES-256 encryption.

*Scrambled transmissions can be decoded in real time by anyone with basic knowledge and equipment. If you want to secure your transmissions you should employ encryption (preferably AES) not scrambling