ComStream CM601, Installation And Operation Manual

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Installation 4-13
Step 7:
Validate the System
To validate the system and isolate system faults, the tests described in Table 4-5
can be performed using the modem loopback (MLB) command.
Remember to perform the series of loopback tests from both ends of the satellite
link. This will ensure that each modem is receiving the carrier from the satellite
with an acceptable E
b
/N
0
level within the anticipated link availability. Typical
levels range from 6 to 10 dB.
For detailed testing information and procedures, refer to the chapter on
troubleshooting and maintenance.
Table 4-5 CM601 System Tests
Test Description
Near data loopback Validates the connection between the DTE and the CM601.
IF loopback Validates IDU operation; can only be performed using an external
loopback cable.
Satellite loopback Validates the coaxial cabling between the CM601 and the RF equipment;
confirms the radio transmit and receive paths and the satellite receive and
transmit paths.
Far data loopback Validates the entire transmit and receive paths between the near-end DTE
and the far-end modem. The far-end modem must be in far data loopback
mode.
Long-term BER
measurement Indicates if the:
Satellite link is operational 24 hours a day, 7 days a week, with no
periodic interruptions along the way
Doppler effects of satellite motion on the circuit operation are
nonexistent, or at least within tolerance
This test should be performed for one week but at a minimum should be
conducted for at least 24 hours.
The one-week duration is optimum, as neighboring carriers on the satellite
may interfere only at certain times during the week.
This test can be run with an external DTE data integrity tester or the
internal, built-in, BERT available on certain modem cards.