User Manual

SGD-SB2025NT-TUM, Part 1
Jan 12 Page 36 TECHNICAL DESCRIPTION
This application receives packets from one or more NIs every 20 ms, votes the best quality signal
and presents it to a dispatcher either via a DFSI connection or as an analogue 4-wire using an
additional stand-alone Network Interface.
Outgoing analogue or P25 audio/data from analogue dispatcher, DFSI or voted call is time-
stamped and sent to all associated NIs for transmission. If multiple NIs are connected they can be
synchronised to create a simulcast channel.
The TM application stores the complete configuration for the channel on its internal compact flash
memory card. All the configurable settings on all the connected NIs are stored here and are kept
synchronised with the NIs over a control channel that is multiplexed into the 20 ms Ethernet packet
structure.
A number of conditions are monitored throughout the channel and alarms can be raised if
necessary. These can be displayed and acknowledged by the ET or by SNMP using a third party
Network Management System (NMS) using the supplied Management Information Base (MIB).
5.6 S OLAR N ETWORK I NTERFACE
The NI provides the connection between the Ethernet link and the radio base station hardware.
Traffic and control information is multiplexed into fixed length packets and sent to/from the TM
every 20 ms.
There are two CPUs in the NI. One, a PIC, manages the Ethernet interface, the control of the base
station (RSSI, PTT, alarms etc.), the PLL that is locked to the external 1PPS timing signal for
simulcast transmission, the serial ports for the ET and connection to the Micro Controller board,
and the handling of all the configuration data to/from the TM. The other, a DSP, manages all the
analogue signal processing including the C4FM modulation/demodulation, tone detection,
generation and synchronisation, deviation limiter, FM pre/de-emphasis, g.726 encoding/decoding
and in the case of a Central NI, AMBE +2 vocoding.
The Network Interface has two analogue ports. A duplex wide band unbalanced port connects
directly to the Rx’s discriminator output and the Tx’s wideband input. This has a flat frequency
response from virtually DC to over 3.2 kHz to enable P25 C4FM.
The other analogue port is duplex, 600R transformer coupled and is provided for when the NI is
used as an analogue dispatcher interface. This is not used in the SB2025.
There are two serial ports. One connects to the USB serial interface on the Aux PCB and allows
connection of the ET and MxTools applications. The other connects internally to the Micro
Controller PCB and passes information to control the operating condition of the base station,
channel, Tx power etc.
1PPS timing and optionally NMEA data is provided by the Aux PCB when a GPS Rx is connected
to the SB2025.
The 26 way Facilities connector carries the two analogue ports described above an analogue input
for an RSSI voltage from the receiver. Three relay change-over contacts and three opto-isolated
inputs are provided. One relay keys the Tx and two of the inputs are used for Rx mute indication
and alarm status. An RJ45 socket provides the 10BaseT Ethernet interface and is connected
internally to the Ethernet switch on the SBC Support PCB.
Power to the NI is 12 V DC and is supplied by the Aux PCB.