CTCSS / DCS coded squelch selection

In general for narrowband FM two-way PTT radio systems including amateur radio, FRS, GMRS, MURS and CB radio, using CTCSS / DCS is a means to allow a group or subgroup to communicate while not bothering others on a different squelch code. Coded squelch has the side effects of slightly reducing communication range and adding a slight delay to unmuting audio at the beginning of a transmission while the receivers decode the squelch code.

Coded squelch does NOT make communications private, as anyone without coded squelch can hear the audio–the subaudible tone is added to the voice audio, but does not scramble the audio.

Unless there is a specific need, users should generally use CTCSS to avoid unmuting delays and range loss that are noticeably worse with DCS. DCS is for crowded areas where range loss isn’t important, and where the user wants to avoid CTCSS interference from other users. By default use CTCSS unless you are really having a problem with not enough tones to pick from. DCS is a last resort.

Historically, lower frequency CTCSS tones had a longer unmute delay, but modern radios minimize this impact. Avoid tones that are near harmonics of the AC mains frequency in the area (50 Hz or 60 Hz typically).

In particular, CB Radio use among family groups and convoys is dramatically improved by using CTCSS to avoid interference from other users and “skip” on the 27 MHz band from users hundreds or thousands of miles away. CTCSS also avoids nuisance opening of squelch from power lines, computers, etc.

Particular to CB radio, the receiver may have an RF gain control that can be used to reduce the sensitivity of the receiver to avoid interference from strong signals. With CTCSS, one might leave the RF Gain on “auto” or maximum (“off” on Anytone family of radios) and use auto noise squelch “ASQ” to maximum communication range while protected from noise by coded squelch.

Sub-$100 CB radios that have CTCSS include the Radioddity CB-500 and the Radioddity CS-27. Anyone buying CB radio for family, group, or convoy use should strongly consider a CB radio with CTCSS.

Reference: very detailed history of subaudible squelch by Repeater Builder.