Handbook

Axell Wireless Limited
Technical Literature
WMATA CRCS Redundant Antenna System
General Overview
Document Number 60-228701HBK Issue No. 3 Date 28/05/2010 Page 48 of 114
4.8. Dual Fiber Optic Unit 60-228703
Dual Fiber Optic Unit 60-228703 is built into a 2U, 19” rack-mount case.
Downlink RF from Splitter/Combiner Unit 60-228702 enters the Dual Fiber Optic Unit via the N type port
labeled “TX 1” (annotated “A” in section 4.8.4.) and passes through a 20dB Directional Coupler 90-852420
which couples off a small portion of the signal and feeds it to the N type port labeled “MON -20dB TX 1”
(annotated “B” in section 4.8.4.) which provides a 20dB test/monitor port for the Downlink input.
The main Downlink path then passes into a Fiber Optic Transmitter Module 20-005401 where the RF signal
is modulated onto a laser and the optical signal thus produced then exits the Dual Fiber Optic Unit via the
SC/APC optical port 1 “TX” (annotated “C” in section 4.8.4.) and is transmitted to the Gallery Place Station
CRAS System via a fiber optic cable link, this is the Main Redundant optical Downlink signal.
The N type port labeled “TX 2” (annotated “D” in section 4.8.4.) is a Downlink input to a separate, parallel,
Standby Redundant Downlink path with its own Directional Coupler, test monitor port (annotated “E” in
section 4.8.4.) and Fiber Optic Transmitter Module. The Optical output from the Standby Redundant
Downlink path exits the Dual Fiber Optic Unit via the SC/APC optical port 2 “TX” (annotated “F” in section
4.8.4.) Switching between the Main Redundant and Standby Redundant Downlink paths is accomplished
manually by disconnecting the Downlink RF input from the “TX 1” port and connecting it to the “TX 2” port,
and by disconnecting the optical Downlink output cable from the SC/APC optical port 1 “TX” and connecting
it to the SC/APC optical port 2 “TX”. N.B. The safety precautions noted in section 2 must be observed when
changing from Main to Standby Redundant.
The Main Redundant Uplink optical signal from the Gallery Place Station CRAS System enters the Dual
Fiber Optic Unit via the SC/APC optical port 1 “RX” (annotated “G” in section 4.8.4.) and passes into a Fiber
Optic Receiver Module 20-005501 which demodulates the Uplink signal to RF and the Uplink RF signal then
passes through a 20dB Directional Coupler 90-852420 which couples off a small portion of the signal and
feeds it to the N type port labeled “MON -20dB RX 1” (annotated “I” in section 4.8.4.) which provides a 20dB
test/monitor port for the Main Redundant Uplink output. The Main Redundant Uplink path then exits the Dual
Fiber Optic Unit for Splitter/Combiner Unit 60-228702 via the N type port labeled “RX 1” (annotated H” in
section 4.8.4.)
The SC/APC optical port 2 “RX” (annotated “J” in section 4.8.4.) is an Uplink input to a separate, parallel,
Standby Redundant Uplink path with its own Fiber Optic Receiver Module, Directional Coupler and
test/monitor port (annotated “L” in section 4.8.4.) The RF output from the Standby Redundant Uplink path
exits the Dual Fiber Optic Unit for Splitter/Combiner Unit 60-228702 via the N type port labeled “RX 2”
(annotated “K” in section 4.8.4.)
Switching between the Main Redundant and Standby Redundant Uplink paths is accomplished manually by
disconnecting the optical Uplink input cable from the SC/APC optical port 1 RX” and connecting it to the
SC/APC optical port 2 “RX”, and by disconnecting the Uplink RF output from the “RX 1” port and connecting
it to the “RX 2” port. N.B. The safety precautions noted in section 2 must be observed when changing from
Main to Standby Redundant.
Dual Fiber Optic Unit 60-228703 is powered by a 24V DC supply from one of the PSU Modules 96-300091
in PSU Housing Shelf 96-300090, The 24V DC supply powers two on-board DC/DC converters 96-200024
arranged in a parallel dual redundant configuration, the outputs of which are combined by power diodes to
provide a 12V DC supply for the fiber optic modules within the unit
An alarm system is fitted to Dual Fiber Optic Unit 60-228703, each of the fiber optic modules carries its own
voltage-free contact alarm relay output which are summed at the 15 way “D” panel plug labeled “ALARM”
(annotated “EE” in section 4.8.4.) which connects to the Krone terminal block located near the top of the
rack (see section 4.3.2.).