Motorola PM1200 User Manual page 27

Radio Firmware Features
DPL signal consists of a continuous sub-audible digital signal
transmitted simultaneously with a voice message. DPL is similar to
TPL except that a digital pattern is transmitted rather than a tone. The
radio will follow the standard for sub-audible Continuous Digital
Controlled Squelch System (CDCSS) that is covered in TIA/EIA-603.
Carrier Squelch operation does not require a sub-audible signal be
decoded in order to unmute the radio's speaker. Likewise, it does not
produce a sub-audible signal during transmission.
9.1 Carrier Squelch Operation (CSQ)
The radio unmutes when the carrier energy exceeds the radio-
designated carrier energy threshold.
When the energy is below the squelch threshold, carrier squelch
detection is not achieved and radio will remain mute.
If a conventional personality is configured via the CPS to transmit
CSQ only, no PL tones/codes will be transmitted.
If a conventional personality is configured via the CPS to receive
CSQ, no PL tones/codes will be checked. The radio will unmute upon
detection of carrier squelch.
9.2 PL Operation
PL is a Motorola term for CTCSS. PL is a sub-audible tone/code used
to create unique/private communication groups. There are two types
of PL, which in generic terms known as Tone Private Line (TPL) and
Digital Private Line (DPL).
9.2.1 Tone Private Line (TPL)
You can select TPL from the CPS for individual personality. Each
personality has different Squelch type to transmit and receive.
PM1200 Mobile Radio with Control Head 15