Uniden UBCD996T - Manual (Page 22)

What is Scanning?
What is Searching?
What is CTCSS/DCS?
Unlike standard AM or FM radio stations, most two-way communications do not
transmit continuously. Your UBCD996T scans programmed channels until it finds an
active frequency, then stops on that frequency and remains on that channel as long
as the transmission continues. When the transmission ends, the scanning cycle
resumes until the scanner receives another transmission.
The UBCD996T can search each of its 9 service search ranges and up to 10 custom
search ranges to find active frequencies. This is different from scanning because
you are searching for frequencies that have not been programmed into the
scanner’s channels. You set the upper and the lower values of the range and then
the scanner searches for any active frequency within the limits you specify. When
the scanner finds an active frequency, it stops on that frequency as long as the
transmission lasts. If you think the frequency is interesting, you can program it into
the scanner’s memory. If not, you can continue to search.
Your scanner can monitor systems using a Continuous Tone Coded Squelch System
(CTCSS) and Digital Coded Squelch (DCS) system, which allow squelch to open
only when the tone you have programmed with a specific frequency is received
along with a transmission.
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. A scanner, such as your UBCD996T, equipped with CTCSS and
DCS, can code each received frequency with a specific sub-audible CTCSS or DCS
frequency or code. Then, when you receive multiple signals, you only hear the
transmission with the CTCSS or DCS tone you programmed. If you do not receive
the correct tone with a signal, the scanner’s squelch remains closed and you hear
nothing.
The tables showing the available CTCSS frequencies and DCS codes are found in
the Reference Section on Page 138 of this manual.
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