Fiber Optics; Loss Budget; Initial Unit Testing - Canoga Perkins 2240 User Manual

Canoga Perkins

1.5.7 Fiber Optics

Each interface signal input to the modem is converted to logic level for use by the
modem circuit. The logic level signal is then multiplexed and encoded into a
biphase data stream, which in turn is converted to optical signal level for transmis-
sion over the fiber optic cable.

1.6 Loss Budget

The maximum possible transmission distance is dependent on the overall power
loss over the fiber optic link. This is called the link loss. The modem's loss
budget is determined by comparing the launch power at the modem with receiver
sensitivity at the other end of the link. The difference is the loss budget.
For reliable operation over a long term, i.e., several years, the link loss should be
at least 3 dB less than the modem's loss budget. This allows for minor increases
in link loss through terminations and any slight deterioration in optical power
output.
The connectors are clearly marked as to their function, either Transmit (Tx) or
Receive (Rx), on the back panel of the 2240 standalone units, and on the rear of
the 2201 Rack Chassis.
The 2240 modem can be used with most popular sizes of multimode and single
mode optic cable; including 50/125, 62.5/125 and 8-10/125.
NOTE: When using 85/125 or 100/140 micron fiber optic cable, an
in-line attenuator may need to be installed between the 2240 and the
Receive (Rx) fiber optic cable for proper modem operation.

1.7 Initial Unit Testing

The Remote and Local Sync indicators on the front panel constantly indicate link
integrity. The Local Sync indicator blinks off momentarily if an error has been
detected. The Loopback Test feature may be used to verify that the fiber optic
modem link and electrical interface are installed correctly.
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