Description
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• power supply function.
It receives the + 12 V direct voltage from the converter and transmits it to the circutis of
the SP board, the RX1/RX2 receivers (for antenna diversity option) and the
TX transmitter. The presence of the power supply is indicated by the green "PWR" LED
on the front of the 3G PA-TRX module in the TRX box.
This function also resets the SP board at each power-up or when the "RESET"
push-button on the front panel of the module is pressed.
The SP board is based around a digital signal processor (SP).
TX transmitter
The TX transmitter is direct modulation type: it has no frequency conversion.
Its function is to supply from the I and Q modulation signals produced by the SP board in
base band, the GMSK modulated RF signal for transmission to the PA function.
Its principal components are a modulator and a synthesizer.
The modulator produces the GMSK modulated signal using the I and Q modulation
information from the SP board and the transmission frequency supplied by the synthesizer.
Modulator start-up is validated by the command TX-ON sent by the SP board.
The purpose of the synthesizer is to provide the modulator with the RF frequency of the
signal to be transmitted according to the programmed frequency contained in the signal
from the SP board. This assembly contains a slaving circuit for the RF signal (generated by
a VCO) on the 6.4 MHz reference supplied by the synchronisation board. In case of slaving
loop locking fault, the synthesizer sends an alarm to the SP board.
RX receiver
A linear, phase coherent, double frequency change RX receiver is used.
Its function is to supply, using the RF reception signal from the duplexer (LNA function), a
signal of frequency IF = 20 kHz to the SP board.
Its principal components are:
• two mixers whose function is to transpose the RF signal into high IF (21.4 MHz), then
into low IF (20 kHz),
• two local oscillator circuits LO1 and LO2 supplying the discreet frequencies to the
mixers, according to the programmed frequency contained in the signal from the
SP board.
These circuits include a synthesizer and a signal phase locking loop LO1 (generated by
a VCO) on the 6.4 MHz reference supplied by the UGR board.
In case of a locking fault, the synthesizer LO1 or LO2 sends an alarm to the SP board.
