What is CTCSS and CDCSS?
The term “Continuous-Tone-Controlled-Squelch-System”
(herein referred to as CTCSS) and “Continuous Digital-
Controlled-Squelch-System” (herein referred to as CDCSS)
shall define a system where the radio receiver (s) are
equipped with tone or data responsive devices which allow
audio signals to appear at the receiver audio output, select
voice processing such as scrambling, select between voice
or data, or control repeater functions, only when a carrier
modulated with a specific tone or data pattern is received.
CTCSS and CDCSS are used for many purposes. In many
cases, CTCSS and CDCSS 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.” You may also need to have your scanner
coded correctly to “hear” the repeater.
CTCSS and CDCSS are also used in areas of high
interference where there are several stations with output
frequencies in close proximity with one another. When this
occurs, you may hear multiple communications at the same
time. The stations could even interfere with each other to
the point where it is impossible to clearly receive either
one. When your receiver, in this case, a scanner, is
equipped for CTCSS and CDCSS, you can code each
received frequency with a specific CTCSS and CDCSS
frequency. Then, when multiple signals are broadcast, you
will only hear the transmission with the CTCSS tone or
CDCSS tone you have programmed. If you do not receive
the correct tone with a signal, the squelch of your scanner
remains closed and you will not hear anything.
Establishment of the CTCSS tone and CDCSS tone for
each transmitter (or repeater) is usually done through the
cooperative setting of standards by local frequency
allocation groups.
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