Uniden UBCD996T User Manual

Page 22

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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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