User's Manual

MM102558V1 R1A
5.5.2 P25 Conventional Repeater Station Operation
In the P25 Repeater mode, the DSP Module uses the Delay PTT In line and the Remote PTT to
communicate with the System Module. After the DSP Module demodulates a four-level FM signal, it
asserts a Delay PTT In signal to the System Module, indicating a P25 call is being received. While the
Delay PTT In line is applied, the System Module keys the External PTT and disables the Channel Guard
circuitry, preventing further processing of the 455 kHz signal on the VOL-SQ HI line.
The four-level FM signal is passed onto the System Module on the EXT HSD line. The System Module
processes the signal and sends it to the TX Synthesizer Module on the TX Audio Hi line. The External
PTT also keys the transmitter and the signal is re-transmitted. The DSP module continues to assert the
Delay PTT In line until the P25 Terminating Data unit is transmitted.
While the External PTT is keyed, the DSP passes the demodulated analog audio to the System Module on
the MDM Line TXD. The System Module routes the audio to the landline interface for monitoring by the
Console.
5.5.3 P25 Conventional Station with Console
5.5.3.1 Console Transmit
The MASTR III P25 Conventional Base Station also supports analog remote control through the base
station’s 2- or 4- wire landline interface. When communication is initiated by a remote console, the
analog audio is routed through the Interface Card to the System Module. The System Module routes the
audio on MDM Line RXD to the DSP Module. The System Module also sends a Remote PTT signal to
the DSP Module, initiating the four-level FM modulation process.
The DSP Module asserts a Delay PTT In signal to the System Module, indicating a P25 is being sent.
The System Module executes an External PTT, this keys the transmitter and the signal is transmitted. The
modulated four-level FM signal is passed on to the System Module on the EXT HSD line. The System
Module processes the signal and sends it to the TX Synthesizer Module on the TX Audio Hi line. The
DSP module continues to assert the Delay PTT In line until the call is complete and the P25 Terminating
Data unit is transmitted.
5.5.3.2 Console Preempt
The Console Preempt feature allows a dispatcher’s call to preempt a radio call already in progress. This
means the dispatcher’s call is heard by all radios and the transmitting radio is still heard by the dispatcher.
The Console Preempt feature assumes a P25 call is in process (see section 4.2). When the console
initiates a call, the analog audio is routed through the Interface Card to the System Module. The System
Module routes the audio on MDM Line RXD to the DSP Module and sends a Remote PTT signal to the
DSP Module.
The DSP Module initiates the four-level FM modulation process of the console audio. It then switches
from sending the P25 call to sending the four-level FM modulated console audio to the System Module
on the EXT HSD line. The System Module processes the signal and sends it to the TX Synthesizer
Module on the TX Audio Hi line. The System Module continues executing an External PTT, keying the
transmitter and transmitting the console signal.
At the end of the console call, the DSP Module sends the P25 Terminating Data unit. If the P25 Repeat
call still exists, the DSP Module continues to assert the Delay PTT In line until the call is complete and
the P25 Terminating Data message is transmitted.
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