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CHAPTER 5: Troubleshooting and Diagnostics
Figure 5-5. Fiber Optic Modem BER System Test (Two-BERT Test).
5.4 (Local) Analog Loopback Test
This test checks the performance of the local modem, the local data terminal
equipment, and the cables between them. It runs separately at the local and
remote sites.
1. Press the ANA pushbutton on the front panel. (This test can also be activated
via the pin on the DTE interface.) The TEST LED should light. The Fiber
Optic Modem transmit output is now connected to its own receiver.
2. Verify that the data terminal equipment is operating properly and can be
used for the test. If it is faulty, call a technician to replace the unit.
3. Execute the test using one of the following methods:
• Use the DTE and check the echoed data stream.
• Use an external Bit Error Rate Tester (BERT) unit.
• Use the internal BERT. Press the PATT pushbutton on the front panel;
the TEST and RTS LEDs light constantly while the ERR LED lights briefly
to indicate that the lamp is functioning. If a bit error is encountered, the
LED blinks or remains lit.
4. Perform Step 3 at both ends.
Fiber Optic
Modem
Fiber Optic
Modem
PATT Pressed
(Disconnects
External DTE)
PATT Pressed
(Disconnects
External DTE)
