ComStream CM601, Installation And Operation Manual

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8-14 Fault Handling, Troubleshooting, and Maintenance
IF Loopback Test
The IF loopback tests the CM601 transmit and receive paths, including IF
modulation and demodulation, as illustrated in Figure 8-2. This loopback test also
uncovers timing problems between the DTE and the CM601.
Figure 8-2 IF Loopback
To place the CM601 in IF loopback testing mode:
1. Install the provided loopback cable between the modem’s Tx IF connector and
the Rx IF connector.
2. Set TS and RS to the same frequency.
3. Program all other CM601 receive parameters to match the transmit
parameters.
4. Enable the modulator by either issuing a remote
LB 1
command or the front
panel
Loopback IF
command.
If error-free data is not received by the DTE, verify:
Installation of the IF loopback cable
Clocking configurations for the DTE and CM601
A successful IF loopback test is performed when the DTE transmits and receives
its own data error free. This is indicated by:
A green Rx Sync LED
No fault messages received once the clear faults command is issued
If the CM601 is equipped with the optional BERT, it can be used instead of the
DTE to indicate a successful IF loopback test. For information on the CM601
BERT, refer to the appendix on internal BERT.
G629-01
DTE
CM601
Local Site
CM601
Remote Site
Satellite