Digital Signal Squelch & Access Operation; Network Access Code (Nac) - Futurecom PDR8000 Manual

6.6.2 D S
IGITAL IGNAL
When evaluating a digital/P25 radio signal, PDR8000 is configured to process the received
signal based on having the Received Signal Strength (RSSI) surpass a configured threshold.
The RSSI threshold level can be set independently for each channel. A common setting (across
all channels in the active Deployment Profile) is used to determine the RSSI measurement
integration time (speed) and hysteresis value for RSSI un-detect.
Once PDR8000 determines that the received signal has met the configured Signal Strength
criteria, it next evaluates the signal content to determine whether it should further process the
signal. This content analysis is based on configuration of whether the PDR8000 should be
additionally dependent on receiving specific access codes in the digital bitstream. This
signalling comes in the form of a P25 NAC (Network Access Code). Sophisticated configuration
capability exists to set up the NAC criteria using Access Code Tables (see sections below).
When PDR8000 transmits a digital RF/CAI signal, it is configured to include a Network Access
Code to control which subscriber units receive/process the call. This is also configured through
the Access Code Tables explained below.
Note that another method also exists that may be used to selectively share/hide signals on P25
conventional channels in order to allow different user groups to cooperatively share an RF
channel; this is the concept of Conventional Talkgroups (further discussed in 6.21).
6.6.2.1 N
ETWORK
The Network Access Code or NAC is a feature of Project 25 digital radios that operates similarly
to PL/DPL codes for analog radios. NAC codes minimize co-channel interference and allow
repeater addressing by keeping the receiver squelched unless a signal with a matching NAC
arrives. NACs are programmed as a 3-digit hexadecimal code that is broadcast along with the
digital signal (Voice, Data, or Supplementary Data) being transmitted.
Since the NAC is 3-digit hexadecimal number (12 bits), it gives 4096 possible NACs for
programming.
Three of these NACs have special meaning:
$293 - the default NAC
$F7E - Receiver Monitor; a receiver set for this NAC will unsquelch on any NAC
received
$F7F - Community Repeater; a repeater receiver set for this NAC will allow all incoming
signals to be repeated with the NAC intact.
PDR8000 allows each of its digital-enabled channels to be configured with a desired behavior
for utilizing NACs. These behaviors are captured in Access Code Tables. Each configured
channel in the PDR8000 can point to one of the configured Access Code Tables. Each Access
Code Table can be used to define NAC operation for a specific channel, or may capture
behavior shared by multiple channels.
2021-11-15
S & A
QUELCH
A C (NAC)
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PDR8000® Portable Digital Repeater Product Planner
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CCESS PERATION
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