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VT-4R150 VHF Project 25 Digital Transmitter Instruction Manual
2-9
2.13.2.6
Audio Pre-emphasis
For analog channels, the standard 6 dB/octave pre-emphasis curve may be either disabled or
applied to the transmitted audio. Pre-emphasis is applied to audio from the Unbalanced Audio
Input, the microphone input, and the audio input on the CNTL BUS jack on the front panel.
2.13.2.7
Timeout Value
This option allows selection of one of four preset timeout timer values. Each of the four preset
values is set in the Transmitter Wide Settings panel, in the section called Timeout Options. If the
transmitter is keyed continuously for longer than the selected time, it will be de-keyed. To reset
the timeout timer, the applied PTT* signal or ANALOG_COR* or DIGITAL _COR* signal must
be removed for a period at least as long as the hang time.
2.13.2.8
Project 25 Squelch Settings: Network Access Code (NAC)
For P25 channels, the transmitted Network Access Code can be set here. The Network Access
Code (NAC) is a 12 bit field embedded within every P25 voice call.
NACs are primarily used for two purposes:
1) They allow a large system coverage area to be serviced by separate repeaters.
2) They allow multiple repeaters to service multiple systems with overlapping coverage areas.
NACs achieve these functions by minimizing co-channel interference. This is done by
keeping the receiver squelched unless a signal with a matching NAC arrives.
The NAC's 12 bit field ranges from 0 to 4095 (hexadecimal $0 to $FFF). The default value is
$293 and two values are defined for special functions.
1) When a receiver is set for NAC $F7E, it unsquelches on any incoming NAC.
2) If a repeater receiver is set for NAC $F7F, it also unsquelches on any incoming NAC.
When the P25 Compliant repeater is released, $F7F allows the repeater to repeat any
incoming NAC.
2.13.2.9
Project 25 Squelch Settings: Talk Group ID (TGID)
The transmitter’s Talk Group ID can be set here. This applies to Project 25 signals only
The Talk Group Identifier (TGID) is a 16 bit field embedded within every P25 voice call. The
purpose of a Talkgroup is to allow logical groupings of radio users into distinct organizations.
The TGID's 16 bit field ranges from 0 to 65,535 (hexadecimal $0 to $FFFF). Three of these
values are set up for special functions.
1) The default value of $1 should be used in systems where no other talkgroups are defined.
2) A value of $0 corresponds to "no-one" or a talk group with no users.
3) A value of $FFFF is reserved as a talk group which includes everyone.
2.13.2.10
Analog Signaling Settings: Signaling
This setting may be set to No Tone, CTCSS or DCS. When either CTCSS or DCS Squelch Type
is selected, additional combo boxes appear to allow selection of a particular tone or code.