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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.
What is CTCSS/DCS?
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 BCD996T, 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 of this manual.
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 1980s, 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
•
FRS/GMRS users
•
Broadcast AM/FM/TV stations
•
Many business radio users
When you want to store a conventional system, all you need to know is the frequencies they operate on. When you are scanning a
conventional system, the scanner stops very briefly on each channel to see if there is activity. If there isn't, the scanner quickly
moves to the next channel. If there is, then the scanner pauses on the transmission until it is over.
Simplex Operation
Simplex systems use a single frequency for both transmit and receive. Most radios using this type of operation are limited to line-of-
sight operation. This type of radio is frequently used at construction job sites, and with inexpensive consumer radios such as
GMRS/FRS radios. The range is typically 1-15 miles, depending upon the terrain and many other factors.
Repeater Operation
Repeater systems use two frequencies: one transmits from the radio to a central repeater; the other transmits from the repeater to
other radios in the system. With a repeater-based system, the repeater is located on top of a tall building or on a radio tower that
provides great visibility to the area of operation. When a user transmits (on an input frequency), the signal is picked up by the
repeater and retransmitted (on an output frequency). The user's radios always listen for activity on the output frequency and transmit
on the input frequency. Since the repeater is located very high, there is a very large line of sight.
Typical repeater systems provide coverage out to about a 25-mile radius from the repeater location.
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