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3CC08991ATAA TQ BJA 01
Issue 01 -- March 2004
2.2.1.3 -- IDU/ODU cable
A coaxial cable, only available in 50 ohm impedance version, with a maximum length of 300 meters (when of
standard type), connects the IDU to the ODU. This carries:
--
the digital data streams between the IDU and the ODU, comprising:
S
the aggregate obtained from tributary multiplexing,
S
the ODU control signals,
S
in the case of a classic IDU, the IDU/ODU telephone channel (connected to ESC N
_
2).
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the ODU’s primary DC power supply voltage.
2.2.1.4 -- OutDoor Unit (ODU) operation
The reference of the outdoor unit depends on the frequency band.
The cable interface handles:
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reception and transmission of the data streams,
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separation of the signals and the power supply voltage to feed the unit’s subsystems,
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the interface for the aggregate, for transmission or reception, with the modem.
The Modem (modulator/demodulator) function receives the aggregate from the cable interface and processes
the baseband signal for microwave transmission by 4QAM or 16QAM modulation, as follows:
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in transmission:
S
digital filtering and error correction coding (FEC),
S
digital/analogue conversion of bit streams I and Q from the encoding function;
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in reception:
S
a part of the automatic gain control (AGC) function,
S
analogue/digital conversion of the I and Q bit streams from the demodulation function.
It interfaces with the IF unit for the transmit and receive the I and Q bit streams.
The IF block handles modulation and demodulation of the aggregate, using the following functions:
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in transmission:
S
analogue filtering of the I and Q bit streams (two filters that can be switched according to capacity),
S
4QAM or 16QAM modulation of an IF carrier, according to the frequency plan adopted, generated
by a local internal oscillator,
S
level amplification and tuning (AGC), based on measurement of the rms power output from the
block;
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in reception:
S
amplification, with AGC, of the received signal, transposed via the receive system according to the
frequency plan adopted,
S
demodulation of the signal, so that the I and Q bit streams can be recovered,
S
amplification and analogue filtering of the bit streams (two filters that can be switched according
to capacity),
S
amplification, with AGC, before transmission of the I and Q bit streams to the Modem board.
The transmit mixer transposes the intermediate frequency to a microwave frequency. Frequency agility is
obtained by a synthesized local oscillator (LO).
The transmit RF signal is then transmitted to the power amplifier, monitored by an output power slaving device
and a circuit for cutting off carrier transmission if a fault is detected in the transmit circuits.
Summary of Contents for 9400 UX
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