User's Manual

DMR repeater 24/01/2011 Versione 1.1
Documento Riservato - non divulgabile senza autorizzazione
Pag. 5 / 55
∞ Frequency self-tuning device
∞ Deviation self-calibration device
∞ Analogical and digital demodulation
∞ RF circuits testing
∞ Phase modulator calibration
∞ RF output power control
∞ Low frequency lines management
∞ DMR protocols management
∞ Digital signals processing
∞ Management, conditioning and routing of traffic and remote control signals from and towards
external world
Receiver can be supplied as single or double for space diversity reception. Main and diversity channels are
completely independent and coherent (sharing the same local oscillators) and they are designed according to
an heterodyne structure, with vectorial conversion to base-band.
Channel standard bandwidth is 12.5 KHz, but the receiver is prepared to accept also a settable channel
bandwidth of 25 KHz, 20 KHz, 10 KHz (with double funnel option) for special applications.
Receiver module is managed by a microcontroller unit whose program is hosted inside internal e2prom flash
memory to lower parasitic emissions. This FW can be loaded through serial connection. The microcontroller, in
addition to managing internal function of the unit, transfers measured parameters to the control unit through
115.2 Kb/s serial line.
The board is realized with surface mounting components (SMD) to maximally reduce dimensions.
On the frontal panel 2 LEDs are placed for monitoring internal PLLs lock status.
Transmitter module is realized with surface mounting components (SMD) and it is housed in a shielded, 8TE
box for 220mm Eurocards, with an heatsink mounted on side, with a thermal resistance of about 1.2°K/W. The
unit can be extracted from the front side of the rack. On the frontal panel two LEDs are placed to monitor the
transmitter status.
Base-band functions, equalizing, limiting, low-pass filtering end eventual emphasis functions are performed by
the DSP unit, which provides also for nominal and maximum deviation calibration by looping modulator with
receiver.
Modulator is digital vector, then the synthesized signal by local oscillator implements the frequency shifting of
the signal which has been directly modulated in base-band by DSP unit and transferred to transmitter through
its I and Q components.
The amplifier is realized by three cascaded stages and RF output power regulation (between 1 and 25W) is
implemented by controlling the 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.