Digital Private Line (DPL)

DPL is a form of digital-coded squelch (DCS) that superimposes sub-audible (not able to be heard) digital data/codes onto the transmitted carrier so that the receiving radio will only receive calls from radios with specific DPL codes. This allows for more use and privacy on a frequency, thereby creating communications groups while operating in Conventional communications mode. Also known as Channel Guard, Quiet Call, and CTCSS.