Continuous Tone Coded Squelch System

This is the AQA version closing after June 2019. Visit the the version for Eduqas instead .

To gain access to revision questions, please sign up and log in.

CTCSS

Some VHF transceivers use CTCSS.
This is a continuous tone below 300 Hz.
The receiver is only activated if the correct CTCSS tone is present.
This allows different organisations to share the same frequency without having to listen to each others' transmissions.
This technique allows better use to be made of the limited number of channels available.
The CTCSS tone is filtered out by the receiver and not passed to the loudspeaker.
The range of frequencies needed for voice communication is 300 to 3000 Hz.
Filtering out frequencies below 300 Hz has little effect on the audio quality.