English 73
CTCSS and DCS are sub-audible tone signaling systems sometimes
referred to as PL or DPL (Motorola’s trademarked terms for Private Line
and Digital Private Line respectively). CTCSS and DCS are used only for
FM signals and are usually associated with both amateur and
commercial two-way frequencies. These systems make use of a special
sub-audible tone that accompanies a transmitted signal.
CTCSS and DCS are used for many purposes. In many cases, CTCSS
and DCS are used to restrict access to a commercial repeater, so that
only those units which transmit the correct tone along with their signal
can “talk” to the repeater.
CTCSS and DCS are also used in areas that receive interference where
there are several stations with output frequencies close to each other.
When this occurs, you might hear multiple communications on the same
frequency. The stations might even interfere with each other to the point
where it is impossible to clearly receive any of the stations. Your scanner
can code each received frequency with a specific sub-audible CTCSS
tone or DCS code. Then, when you receive multiple signals, you only
hear the transmission with the CTCSS tone or DCS code you
programmed. If you do not receive the correct tone with a signal, the
scanner’s squelch remains closed and you hear nothing.
Refer to the Reference section of this manual for tables showing the
available CTCSS tones and DCS codes.
Conventional Scanning
Conventional scanning is a relatively simple concept. Each group of
users in a conventional system is assigned a single frequency (for
simplex systems) or two frequencies (for repeater systems). Any time
one of them transmits, their transmission always goes out on the same
frequency. Up until the late 1980’s this was the primary way that radio
systems operated.
Even today, there are many 2-way radio users who operate using a
conventional system:
• Aircraft
• Amateur radio
• PMR users
• Many business radio users
