User Manual

MN021-01
Page 10 of 28
demodulated back to an electrical signal. The data link associated with each remote unit is also
detected and routed to the microprocessor.
Amplification & AGC: Variable amplification is needed to compensate for the variable optical
fibre loss, maintaining a good signal to noise ratio, so that for each link a constant gain is
obtained.
RF Combining: Signals coming from all remotes are combined into a single RF path, filtered and
duplexed into the RF port.
5.4. Remote supply
The local unit provides connection and distribution for –48VDC supply to the remote units, by
means of composite cable, copper wires and optical fibre pairs. Each supply port is protected
against overloads, short and surge with a self-recovery fuse and surge protection. The power
switch will disconnect the remote supply in case of overcurrent.
5.5. Automatic Gain Control
Optical link losses are typically related to:
- Fibre length (0.2-0.4dB/Km @ 1300nm)
- Splices loss
- Optical connectors tolerances and aging
BriteCell™ Fast implements an automatic gain control (AGC) mechanism to maintain constant
RF link gain, regardless of the overall optical link losses. The allowed optical loss per link must
be in the range of 3dB. Losses outside this window will trigger alarms and warnings according
to the following table:
OPTICAL LOSS OPERATION ALARM SEVERITY
0 dB AGC working, constant RF gain none NONE
< 3dB AGC working, constant RF gain none NONE
< 5 dB AGC not working, RF gain
decreases according to 2dB
electrical per 1dB optical
AGC out of range:
red LED flashes
MINOR
> 5 dB
AGC not working, the optical
signal is too low, the receiver is
automatically switched off in
order to reduce the unwanted
noise to the system.
Optical power too
low: red LED
fixed, rela
ys
alarmed.
MAJOR
6. Alarms and settings
Local unit LEDs are fully managed by software according to different severity levels, and
reported as relay contact and visual alarms (LEDs). There are six LED’s on the Local unit.
Four are related to each optical link and remote unit, one is related to local unit, and one is for
power supply.
Figure 5 TFLF Local Unit Status LED’s