Created Tuesday 27 December 2022
Continuous Tone Coded Squelch System (CTCSS) is a selective calling system for FM and ACSB radios that uses a continuous, low-frequency tone transmitted underneath the audio. The low frequency makes the tag tone easy to filter out of the audio before being presented to the user.
Like DCS, CTCSS can serve two purposes: to separate signals from one group of users on a channel from those signals from another group, and to prevent various forms of non-signal interference (such as electrical interference) from activating the receiver.
CTCSS is availble on a wide variety of equipment. It sometimes has some latency in activating, and so may cut off the first syllables of a transmission, if the person speaking is not aware of the need to pause a moment before speaking.