User's Manual

P B L Tunnel Units 1 & 2
Maintenance Handbook
H/book Number:-60-056100HBKMFCC
Issue No:-2
Date:-04/01/2006
Page:-
22 of 63
5.1.2 AFL Fibre Optic Receiver & Transmitter (20-004001, Tx & 20-004101, Rx)
5.1.2.1 Description
The FO units consist of a receiver & transmitter, which modulates the RF signal onto a laser
carrier and transmits it via fibre/optic cable to a receiver unit some distance away where it is
demodulated back to the original RF signal with very small values of accrued attenuation.
Both transmitter and receiver modules have their own dedicated alarm outputs (volt-free
relay contacts) which are integrated/summed into the main alarm system. The alarms are
non-latching, so an alarm condition may revert to ‘good’ if the fault clears for any reason
(e.g. momentary DC power loss).
The AFL Fibre Optic transmitters and receivers both have two LED status indicators, one
on each module showing DC power and the other indicating ‘Laser On’ for the transmitter,
and ‘Carrier Being Received’ for the receiver.
Typically the input to transmitter units will be at a level of between –30 and –15 dBm. The
RF gain of a pair (Tx to Rx) units is factory set to give a 0dB gain, but this is with a short,
low loss fibre. In determining the performance of any link, the insertion loss of the fibre and
any power splitters fitted must be considered. A general rule of thumb figure would be
around 0.5 - 1.5dB loss per fibre Kilometre.
The fibre optic transmitter module (20-004001) takes two RF inputs, one containing signals
between 20- and 35 MHz (generally used by laser-modems for carrying alarm, and status
information between sites) and another containing signals between 70 MHz and 2.5 GHz
(the main RF carrier) and modulates them both onto to a fibre optic cable. The Laser Tx
module uses a Class IIIa Transmitting Laser Device, see laser safety precautions in section
1. The receiver module (20-004101) takes a fibre optic signal, and converts this into two RF
outputs, one containing signals between 20- and 35 MHz and another containing signals
between 70 MHz and 2.5 GHz.
5.1.2.2 Fibre Optic Units Technical Specification
PARAMETER SPECIFICATION
Fre
q
uenc
y
ran
g
e
(
Traffic
)
70-2500MHz
Fre
q
uenc
y
ran
g
e
(
‘Data’
)
20-35 MHz
Tx Max. O
p
tical Out
p
ut Power
+10dBm
6
1.5
Rx Alarm:
@
10dBm Fibre Loss
Gain
(
back-to-
b
ack connection
)
+10dB
Flatness 70-2500MHz +/-1.5dB
IP3
(
All conditions
)
>+30dB
m
Noise Fi
g
ure
(
back-
b
ack connector
)
: <40dB
Power Su
pp
l
y
: 12V DC –Ve GND
350mA
(
t
yp
ical
)
@
12V DC
(
Rx
)
Consumption:
100mA
(
t
yp
ical
)
@
12V DC
(
Tx
)