User's Manual

Operation DMH Series VHF Radio
Page 3-6 BK RADIO
3.6.2 APCO PROJECT 25 SQUELCH CONTROL
Network Access Codes (NACs) provide the digital equivalent of analog sub-audible
signaling (CTCSS/CDCSS) allowing a group of radios to be selectively called within a
system.
Users in the same area (using the same NAC) can be further divided into Talk
Groups, with each group having its own Talk Group ID (TGID). Group Calls are
made by designating both the users’ NAC and TGID.
Each radio also has an individual P25 unit ID. A Unit-to-Unit call contains the
addressee’s NAC, and uses the addressee’s P25 unit ID instead of the TGID.
When operating in Digital Mode, each channel can be programmed to use either
Normal squelch or Selective squelch.
A. Normal Squelch
Normal squelch is used to mimic analog operation. Signals are only qualified
with the programmed NAC. TGIDs and P25 Unit IDs are ignored. Each digital
channel is programmed with a receive NAC and a transmit NAC. When an
incoming signal’s NAC matches the channel’s programmed receive NAC, the
radio unmutes. The default NAC is 659 ($293 hex). The digital equivalent of
carrier squelch is achieved by programming the receive NAC = 3966($F7E hex)
the radio will unmute when a digital signal with any NAC is detected. The 3966
($F7E hex) NAC is reserved for receivers and is not allowed as a transmit NAC.
B. Selective Squelch
Selective squelch is used for processing ‘Group Calls’ and ‘Unit-to-Unit Calls’.
TGIDs are assigned on a per-channel basis. Users can be separated into Talk
Groups with each group having its own TGID. Then, on channels programmed
for Selective squelch, the incoming signal’s NAC and TGID must match the
channels programmed receive NAC and TGID for the radio to unmute. The
default TGID is 1. The TGID value 65535 ($FFFF hex) is used to effect an “All
Call”. If the radio receives a signal with a matching NAC and the TGID = 65535
($FFFF hex), it will unmute. Also, if the radio’s programmed TGID is 65535
($FFFF hex), it will open on any signal with a matching NAC, ignoring the
incoming TGID. A TGID = 0 means “no one”. If the radio is programmed with the
TGID = 0, it will accept incoming group calls containing the “All Call” TGID, and
correctly addressed Unit-to-Unit calls.
3.6.3 CHANNEL GUARD RECEIVE
Turn power on by pushing and releasing the Volume knob. The radio will beep,
indicating that it has passed its self test and is operational.
Set volume by pressing the [MON] button to hear squelch noise. Turn the Volume
knob to set a comfortable volume level. Press the [MON] button again to stop
squelch noise.
Select a channel group (if applicable) by pressing the [GRP] button and turning the
Channel Selector knob. Press the [GRP] button again to return to Channel Select
mode.