3085-rwt & 3085-rwr.ib.doc
Page 3 of 10
18-07-02
Description
The IRT RWT-3085 / RWR-3085 wide band RF fibre optic link is a modular system for transmitting a broadband
RF signal ranging from 20 MHz to 200 MHz along a single mode optical fibre. A system consists of two IRT
Eurocard modules, the RWT-3085 LASER transmitter module and the RWR-3085 photo-diode receiver module.
RWT-3085 Laser transmitter.
As shown on diagram 803950 the RWT-3085 Laser Transmitter module consists of a 1300 nm wide bandwidth laser
diode, whose operating current is set by a driver circuit controlled by feedback from the monitoring diode in the laser
package. Wide band amplifiers are used to drive the laser with the RF signal applied to the module input.
The monitoring diode output is also connected to comparator circuits which are used to provide optical power
alarms. The low power alarm drives a LED indicator on the front panel, and after passing through a relay, is also
available as an external connection. The adjustment and connection data for this circuit is given in the installation
section of the manual.
The power supply comprises two bridge rectifiers whose rectified outputs are paralleled (positive and negative
respectively) to provide redundancy. The input to these rectifiers are two independent feeds of 28 Vac (centre tap
grounded). The rectified DC outputs are regulated by three-terminal regulators. The DC indicator LED on the front
panel is wired in series with a zener diode and a resistor b12 and -12 Volts. The zener is to ensure that the
LED extinguishes if either of the power supplies fails.
RWR-3085 Photo-diode receiver.
As shown on diagram 803955 the RWR-3085 Photo-diode Receiver module consists of a 1300 nm optical detector
diode circuit with integral pre- amplifier followed by an attenuator circuit and signal output amplifier. An optical
input level indicator circuit is provided to indicate the loss of input signal to the module.
The optical detector circuit consists of a photo-diode, biased from a +6V supply, followed by an internal amplifier
operating from -5V. The output of the amplifier is connected to a FET amplifier whose gain is controlled by its bias
which is set by a front panel control. A further amplifier is used to bring the output level up to the level applied to the
input of the RWT-3085 Laser Transmitter.
The bias current to the photo-diode is a measure of the optical signal level received and this current is monitored by
a comparator circuit which provides an alarm when the signal drops below a preset threshold. The low signal alarm
circuit drives a LED indicator on the front panel, and after passing through a relay, is also available as an external
connection. The adjustment and connection data for this circuit is given in the installation section of the manual.
The power supply comprises two bridge rectifiers whose rectified outputs are paralleled (positive and negative
respectively) to provide redundancy. The input to these rectifiers are two independent feeds of 28 Vac (centre tap
grounded). The rectified DC outputs are regulated by three-terminal regulators. The DC indicator LED on the front
panel is wired in series with a zener diode and a resistor b12 and –5.2 Volts. The zener is to ensure that the
LED extinguishes if either of the power supplies fails.
IRT
Communications
www.irtcommunications.com