NEC PASOLINK, Training Course

Page: 30 / 110

FUNCTIONAL OPERATION
ROI-S04488
2-20
Fig. 2-3 PSK Modulation
2.3.3 Orderwire Signal Modulation
To facilitate an EOW between the IDU and ODU, the EOW signal is
amplitude-modulated with the 450 kHz carrier by the orderwire modulator
(EOW MOD) on the MOD section. The modulated EOW signal is filtered
to eliminate higher out-of-band noise, amplified up to the required level
and combined with the 850 MHz IF signal through a band-pass filter
(BPF). This eliminates lower out-of-band noise, receiving IF signal (70
MHz), and an arrester (ARSR) protecting the equipment from harmful
voltages caused by lightning.
2.4 Demodulation
This section describes the EOW and alarm signal demodulation, main
signal demodulation and differential decoding.
2.4.1 EOW and Alarm Signal Demodulation
The received (RX) signal from the ODU contains a 70 MHz IF signal, 468
kHz amplitude-modulated EOW signal and 10 MHz ASK-modulated
alarm (ALM) signal. The RX signal is branched into two separate signals;
One is sent to the DEM section through the BPF which eliminates the
transmitting IF, EOW and ALM signals, and the other goes through a BPF
which eliminates the 70 MHz IF signal. The orderwire demodulator (EOW
DEM) demodulates the 468 kHz amplitude-modulated EOW signal. The
demodulated 10 MHz ASK alarm signal is sent to the CPU for further
processing.
P
-L
Q
-L
+L
+L
π
π
/2
3
π
/2
0
STATUS P CHANNEL Q CHANNEL
1(0) -L -L
2(
π
/2) -L +L
3(
π
) +L +L
4(3
π
/2) +L -L