NEC PASOLINK, Training Course

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ROI-S04605
FUNCTIONAL OPERATION
2-3
2.2 Receiver Section
This part describes RF-to-IF conversion, IF-to-IF conversion and EOW
signal modulation.
An RF signal received from the antenna are filtered by the BPF and enters
the first MIX. The first MIX mixes the applied RF signal with an local
signal which is generated by a synthesized RF local oscillator to produce a
first IF signal. Then, the IF signal is fed to the second MIX through the
BPF which eliminates undesired components. The second MIX mixes the
1st IF signal with a local signal generated by a synthesized IF local
oscillator to produce a 70 MHz IF signal.
The 70 MHz IF signal passes a 70 MHz BPF which eliminates undesired
components. The filtered 70 MHz IF signal goes to the main IF amplifier
(MAIN IF AMP). The IF signal amplified by the MAIN IF AMP with
automatic gain control (AGC) passes through the MPX circuit.
The MPX circuit combines alarm, monitoring and response signals which
are processed at the CPU in the ODU and the EOW signal with the IF
signal. These signals are fed to the IDU from the MPX circuit.
2.3 Alarm and Control Section
Alarm and control functions of the ODU are described here. Fault
detection circuits are provided in the ODU. The detected alarm signals are
gathered into the CPU which processes the alarm signals to be sent to the
IDU. Here, the TX PWR ALM signal is produced by the T PWR MON
signal issued from the RF AMP circuit and the IF INPUT ALM signal is
produced by the TX IF LEV MON signal issued from the IF amplifier with
AGC AMP circuit. The RX LEV ALM is also produced by the RX IF
LEV MON signal issued from the MAIN IF AMP circuit. The initiated
alarm signals are sent to the IDU combined with the IF signal through the
MPX circuit. Fault in the ODU can be monitored with alarm indicators on
the IDU. The received RF signal level can be monitored at the RX LEV
MON jack of the ODU by connecting the OW/RX LEV Monitor (optional)
or digital voltmeter.
In addition, the following operating condition of the ODU are monitored at
the IDU by connecting the personal computer.
• Transmitter output power
• Received signal level
• DC voltage