User's Manual

DMR repeater 18/02/2011 Versione 1.3
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Pag. 10 / 32
The amplifier is realized by three cascaded stages and RF output power regulation (between 1 and 25W) is
implemented by controlling the gates voltages of MOSFET amplifier stages. Power amplifier works in C class
and ensures a very high efficiency, lowering the needed power from supply system and lowering the thermal
dissipation inside the cabinet. Direct and reflected output power are measured by a directional coupler.
Power control circuit acts in a closed loop and keeps constant the total power at MOSFET drain. Inside the
module a thermal sensor is hosted and it is directly connected to the internal microcontroller which enables
the command for air forced cooling fan of the cabinet if the temperature rises over 85°C. Anyway, if reflected
power or mosfet temperature exceeds protection threshold, regulation circuit will lower output power up to
safe levels for transmitter.
The current flowing into final amplifier transistor is continuously monitored by microcontroller to verify the
correct functioning and to reveal an eventual efficiency degradation.
The module is equipped with an harmonic filter to lower spurious emissions under required levels by existing
regulations.
3
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I
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O
A
A
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N
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D
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S
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E
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R
V
V
I
I
C
C
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E
S
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M
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U
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I/O and Services module is a unit integrating different interfaces and functions, that for some applications can
be optional but for others become essential. For this reason the module can be differently equipped with its
different logical blocks, according to the particular application. The embedded block are the following:
Telephone line interface: 2/4W+E&M line interface to remote analogical audio and perform automatic
routing through telephonic line
Opto-isolated I/O: 2 input + 2 output contacts programmable (both N.O. or N.C.) for remote
monitoring local sensors and remote controlling local actuators
Opto-isolated alarms: two alarms output (1 warning + 1 fatal)
Analogical input: 2 not isolated inputs, 1 for voltage sensing (0..20V referred to ground) + 1 for current
sensing (4…20mA). These input can be connected the first in parallel and the latter in series with the
analogous ones of other similar equipments
GSM/GPRS modem: embedded communication module for remote control if the site is covered by
GSM or GPRS service. It requires only an external passive antenna
GPS receiver: embedded receiver for GPS service, with high precision Pulse Per Second (PPS) output
function in order to synchronize the station. Only an external active antenna is required
RS232 converter: 115.2Kbit/s serial interface for remote control
I/O and services module is equipped with 8 LEDs on the frontal panel to monitor the status of opto-isolated
I/O, the status of GPRS modem and the presence of PPS.
Modular unit is housed in a shielded, 4TE high box for 220mm Eurocards.