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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 specic 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.
Refer to the Reference section of this manual for tables showing
the available CTCSS frequencies 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
• FRS/GMRS users
• Many business radio users
