7
Understanding Scanning
This section provides you with background on how scanning works. You don’t really need
to know all of this to use your scanner, but some background knowledge will help you get
the most from your BC898T.
Understanding Banks and Channels
The memory in your scanner is organized into 10 banks of 50 channels each. Each bank
can contain conventional channels as well as 1 trunking system. For each trunking system,
each bank can also store 10 groups of 10 talk group ID’s (100 per bank).
What is Scanning?
Unlike standard AM or FM radio stations, most two-way communications do not transmit
continuously. Your BC898T 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.
What is Searching?
The BC898T can search each of its 17 bands and up to ten bands together to find active
frequencies. This is different from scanning because you are searching for frequencies
that have not been programmed into the scanner. When you select frequency bands to
search, the scanner searches for any active frequency within the lower and upper 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
one of the banks. If not, you can continue to search.
What is CTCSS/DCS?
Your scanner can monitor systems using a Continuous Tone Control Squelch (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 subaudible tone signaling systems sometimes referred to as PL
(Motorola’s trademarked term for Private Line). CTCSS and DCS are used only for FM
signals and are usually associated with both amateur and commercial two-way repeaters.
These systems make use of a special subaudible 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 at the same time. The stations might even interfere with each
Understanding Scanning
