Base Tech IV P25 Base/Repeater Station
CTCSS or CDCSS signaling adds an additional condition to
carrier squelch operation. In addition to the signal having to
exceed the squelch threshold level, the received signal must also
have the correct CTCSS tone or CDCSS code before the audio
will be passed to the speaker. CTCSS or CDCSS signaling
allows multiple users on the same frequency to hear only signals
which have their correct CTCSS tone or CDCSS code. An on
frequency signal with the correct CTCSS or CDCSS signaling
will be indicated by a lit Busy indicator and speaker unmute
indicator. A Busy indicator with the speaker mute indicator
means that the channel is busy, but the correct CTCSS or
CDCSS signaling is not present.
CTCSS/CDCSS allows multiple users to share the same
frequency. However CTCSS/CDCSS is only useful to
avoid disturbing other users with messages not related to
them. If more than one radio is transmitting at the same
time, this will cause interference. Do not transmit if the
Busy indicator is lit. Wait until the channel is clear before
transmitting.
Digital Receive Operation
When a P25 digital transmission is received, it will be heard if the
required conditions are met. P25 digital signals have several
mechanisms to allow users to hear only conversations intended
for them. A received P25 digital signal will be indicated by lit
Busy and Digital indicators.
The primary condition the P25 digital signal must match is the
Network Access Code, or NAC. The NAC provides much the
same functionality as CTCSS/CDCSS do for an analog signal.
The received signal will only be heard if the NAC from the
received signal is matched to the channel parameters. There is a
special NAC, hexadecimal F7E, which indicates to the receiver
to allow signals received with any NAC to be heard. This
provides much the same functionality as an analog signal without
CTCSS/CDCSS.
The P25 digital signal may be further addressed to everyone, to
a specific talk group, or to an individual unit ID. If the receiver is
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2013, Midland Radio Corporation http://www.midlandradio.com
