40
SYNC/ASYNC FIBER OPTIC MODEM
If BERT test equipment shows no fault, but the data terminal is faulty, follow the
manufacturer’s test procedures for the data terminal. Check the cable connecting
the DTE to the Fiber Optic Modem.
5. After completing the test (or when the fault has been corrected), reset the
ANA pushbutton to the OFF position (Up). Then perform the
Communication Link Tests (see
Section 5.5
).
L
OOPBACK
F
UNCTION
The Local Loopback command is activated by the DTE interface or by the
pushbutton on the front panel.
The Fiber Optic Modem sends “MARK” level or “OFF” state to the Transmit
LED when the command “LLB” is activated, but the signal is directed only to the
Receive input (see
Figure 5-6
). This is an internal test only, with no external
transmission. At the far end, the remote Fiber Optic Modem functions as if it is in
“Loss-of-Signal State,” which is DCD “OFF” and RX data “OFF” or “MARK.”
Figure 5-6. Local Analog Loopback.
Remote Fiber
Optic Modem
ANA
Pressed
