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6.1 System Checkout
6.1.1 General
The system checkout Section is to be used as an aid in setting up a modem within the
earth station. There are tables for use in checking to see if the Eb/N0 is correct, typical
output spectrum, and typical eye pattern and constellation pictures.
6.1.2 Modulator Checkout
The modem supplies a QPSK modulated result of the DATA I/O connector to the IF
output connector (CP1). A typical output spectrum is shown in Figure 6-1. If the output
does not resemble this picture refer to the fault isolation in Section 6.2.1 to locate the
problem.
The first Step in turning up a carrier is to set the output frequency. This is done in the
"CONFIG" menu on the front panel (Sections 3.1.4. and 3.2.1). The "CONFIG" menu
also allows the operator to set the output level, turn the output ON or OFF, set the
scrambler, differential encoder, clock source, and gives access to the test modes for
system check out. Available test modes are RF loopback, BB loopback, and CW mode.
After the output frequency and level is set the output is to be turned ON.
6.1.3 Demodulator Checkout
The demodulator supplies baseband data to the DATA I/O connector that is a result of
the QPSK modulated signal input at the IF input connector (CP2). Clock and data are
recovered, decoded, and descrambled from the input RF signal by the demodulator and
decoder cards.
The input to the demodulator card must be set within the proper frequency and power
level for the demodulator to lock to the signal. Refer to Figure 6-2 and Table 6-1 to
check for proper Eb/N0 level. Figure 6-2 is an example of a 3/4 rate carrier operating at
MN/U-KST12000 Rev. 0
Chapter 6.
MAINTENANCE
6–1
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