Andrew Wireless Innovations Group BCEL-FAST719 User Manual

Page 16  of 28

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

Figure 11  Remote Unit TFAF Block Diagram 

Low noise amplification: the low level signal coming from the antenna and duplexer is amplified 
and filtered.  
 
E/O Conversion: The RF signal modulates the intensity of an optical carrier through an electro-
optic device (laser).  

O/E Conversion: The modulated optical signal coming from the local units is detected and 
demodulated back to electrical signal. 
 
Amplification & AGC: Variable amplification is needed to compensate for the variable optical 
fibre loss, maintaining a good signal to noise ratio, to maintain a constant gain for each link. The 
resultant signal is amplified, filtered and is duplexed to feed the antenna. 

The remote unit is powered with  –48VDC supply, positive to GROUND, by means of composite 
copper wire and fibre cable.  

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: 

DC     DC                -48VDC 

PHOTODETECTO

 

Downlink 

AGC 

VARIABLE 
GAIN AMP. 

D 
A 
C 

A 

DD 

C 

µ

PROC

.  

Diff. AMP 

LASER module

MONITOR PHOTODET. 

LASER DIODE 

VOLTAGE 

CONTROLLED 

ATTENUATOR 

MATCHING 

NETWORK 

UL  ATTENUATOR CONTROL 

SWITCHES 

attenuator 
control 
voltage 

DL final amplifier stage 

current monitor

RF 
SMA  

RF SMA 

50 

Ω

 

Data link  

DC/DC 
converter 

Voltage 

Regulator  

RX optical power monitor 

 

Shut down 
control 

CURRENT 

GENERATOR 

LASER control 
module 

+12 V

-8 V

+5 V

Auxilliary External

alarms 

DC loop