CANOGA PERKINS 2240 Fiber Optic Modem - Manual (Page 98)

98
Canoga Perkins
6.2 Loopback Test Diagnostic Procedure
Step Symptom Possible Cause(s) Action
1 No Sync Indication. Defective fiber optic Continue to the
modem(s), cable(s) to the next step.
or connectors. If the
modems are con-
figured for a tail circuit
(one is externally
locked and the other
is slave), verify that the
externally locked 2240
has a clock on its TT
(or equivalent) leads
that matches its rate
switch.
2 Verify the optical cable loss. Remove the Tx fiber from the modem. Use
the optical power meter and fiber optic jumper cable to determine the
optical launch power for this modem. Reconnect the Tx fiber to the
modem. Remove the Rx fiber from the modem and determine the optical
receive power into this modem. Reconnect the Rx fiber to the modem.
Repeat the above step for the modem at the other end and record both
optical power levels.
Perform the following optical loss calculation:
Near-end Receiver level minus far-end Transmit level = Near-end link
loss figure.
Far-end Receiver level minus near-end Transmit level = Far-end link loss
figure.
If the optical cable loss figure exceeds the optical link loss budget
specified for the modem, set the optical launch power for the modem(s)
to the high power setting and repeat the power measurements (refer to the
"Specifications" section for appropriate loss budget figures). If the actual
cable loss still exceeds the loss budget for the modem, go to Step 3. If
the cable loss is within the specified loss budget for the modem, go to
Step 5.