3810-rwt.ib.rev1.doc
Page 3 of 11
17/10/2007
IRT Eurocard
RWT-3810 / RWR-3810
L BAND RF FIBRE OPTIC LINK
General description
The IRT RWT-3810 / RWR-3810 wide band RF fibre optic link is a modular system for transmitting a broadband
RF signal ranging from 900 MHz to 2050 MHz along an optical fibre. A system consists of two IRT Eurocard
modules, the RWT-3810 LASER transmitter module and the RWR-3810 photo-diode receiver module.
RWT-3810 Laser Transmitter.
The RWT-3810 LASER transmitter module consists of a wide bandwidth LASER diode, whose operating current is
set by a driver circuit controlled by feedback from the monitoring diode in the laser package. A wide band RF
amplifier is used to drive the LASER with the RF signal applied to the module input.
A RF gain control and RF monitor connector are provided on the front panel. The gain of the RF amplifier is
adjusted by the front panel control (RV1), which varies the bias on the attenuator circuit in the RF gain stage.
The gain is adjusted for best signal to noise and inter-modulation performance by setting the RF level at the front
panel RF monitor connector at –40dBm.
The laser internal monitoring diode output is connected to comparator circuits, which are used to provide optical
power indications. The circuits drive LD3 on the front panel for laser power ON and FAIL indication (green for
normal and red for failure), and after passing through a relay circuit, a LASER POWER ALARM is available as an
external connection. The adjustment and connection data for this circuit is given in the installation section of the
manual.
A 10.7 MHz pilot tone generator circuit is provided which with a detector circuit in the RWR-3810 receiver will
verify the RF signal path of the system. The pilot tone level from the generator is monitored by a detector circuit
whose output will be indicated by LD2 (green for normal and red for failure), and can, by closing LK2, operate the
alarm relay circuit if a failure occurs.
LNB DC power can be applied to the RF cable connection to the RWT-3810 by closing LK4 on the board and
applying the required DC voltage to SK3 on the rear panel.
SK3 pin 1 is the ground connection and pin 2 is the active connection. The circuit is not polarity sensitive.
The power supply comprises two bridge rectifiers whose rectified outputs are paralleled (positive and negative
respectively) to provide redundancy. The inputs to these rectifiers are two independent feeds of 28 Vac (centre tap
grounded). The rectified DC is regulated by three-terminal regulators. The DC indicator LED on the front panel is
wired in series with a zener diode b12 and -12 Volts. The zener is to ensure that the LED extinguishes if
any one of the regulators fails.
IRT
Communications
www.irtcommunications.com
