Private Line - CTCSS

CTCSS

In radio or wireless telephony, Private Line is a term trademarked by Motorola to describe their implementation of a Continuous Tone Coded Squelch System (CTCSS), a method of using low frequency subaudible tones to share a single radio channel among multiple users. Each user group would use a different low frequency tone. Motorola's trade name (especially the abbreviation PL) has become a genericized trademark for the method. General Electric used the term 'Channel Guard' to describe the same system and other manufacturers used other terms. A later digital version of Private Line is called Digital Private Line, or DPL.