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 10 of 114
3.3. Dual Fiber Optic Unit 60-228703
Dual Fiber Optic Unit 60-228703 is built into a 2U, 19” rack-mount case.
The Main Primary Downlink RF path from the BTS enters the Dual Fiber Optic Unit via the N type port
labeled “TX 1” (annotated “A” in section 3.3.4.) and 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
TX 1” (annotated “B” in section 3.3.4.) which provides a 20dB test/monitor port for the Main Primary
Downlink input.
The Main Primary 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 3.3.4.) and is transmitted to the Gallery Place
Station CRAS System via a fiber optic cable link.
The N type port labeled “TX 2” (annotated “D” in section 3.3.4..) is a Downlink input to a separate, parallel,
Standby Redundant Downlink path with its own Directional Coupler, test monitor port (annotated “E” in
section 3.3.4.) 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
3.3.4.)
Switching between the Main 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.
The Main Primary 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 3.3.4.) 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 3.3.4.) which provides a 20dB
test/monitor port for the Main Primary Uplink output. The Main Primary Uplink path then exits the Dual Fiber
Optic Unit for the BTS via the N type port labeled “RX 1” (annotated “H” in section 3.3.4.)
The SC/APC optical port 2 “RX” (annotated “J” in section 3.3.4.) 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 3.3.4.) The RF output from the standby Uplink path exits the Dual
Fiber Optic Unit for the BTS via the N type port labeled “RX 2” (annotated “K” in section 3.3.4.)
Switching between the Main 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.
Dual Fiber Optic Unit 60-228703 is powered by a 12V DC supply from Dual Redundant PSU 60-091705,
which powers 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 3.3.4.)