DAS & LCX O&M

DAS & LCX O&M. JAIPUR METRO.

Distributed Antenna System. A Distributed Antenna System or DAS is a network of spatially separated antennas connected to a transport medium – typically coaxial or fiber-optic cable that provides wireless service within a building or structure. Distributed Antenna Systems are designed to amplify two way radio signals in buildings in a safe and efficient manner. DAS’s provide high quality signal, eliminating dropped calls, and also increase call capacity for wireless Telco carriers The DAS can be driven by a direct connection to a radio base station of an “off-air” repeater/signal booster.

Leaky Coaxial cable. used in confined spaces, such as tunnels, mines or large buildings, where natural propagation is inadequate A basic leaky feeder system for two-way communication comprises a base-station Tran receiver / Bi-Directional Amplifier connected to a leaky cable which provides communication to conventional mobile stations. By placing the base station at the centre of the cable the longitudinal range can be effectively doubled relative to an end-fed system.

Leaky Coaxial cable. The basic equation relating the parameters (in dB) of a leaky feeder system is: SYSTEM LOSS = LINE LOSS + COUPLING LOSS Where – SYSTEM LOSS is the ratio of the transmitter output power to the power at the receiver input terminal; LINE LOSS is the longitudinal attenuation of the line between the base station and the point on the line nearest the mobile set; COUPLING LOSS is the ratio of the power in the line at the point nearest the mobile set to the power at the antenna terminal of the mobile set.

System Architecture. the signal sources, Tetra BTS, Police BDA & Fire BDA are combined by 3:1 combiner and the combined signal is connected to the DAS / LCX system for extending the signal coverage Extra BDA‘s are planned at the source to have redundancy in case of any one of the equipment fails. The Output of the BDA’s are connected in parallel to a hybrid 2:1 combiner. The LCX cable and RF cable are used are of LSZH type cable to protect the system from fire..

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System Function. The text describes the communication system setup for TETRA, Police, and Fire services within an underground station or tunnel. Here's a summary of the key components and their functions: Base Transceiver Stations (BTS): These are the communication stations that transmit and receive signals for the TETRA, Police, and Fire systems. Donor Antennas: External antennas installed outside the underground station that receive signals from the BTS. These antennas are connected to the Bi-Directional Amplifiers (BDA) via coaxial feeder cables..

3 . Bi-Directional Amplifiers (BDA): Amplify the signals received from the BTS in both the downlink (signals transmitted from BTS to users) and uplink (signals transmitted from users to BTS). BDAs ensure the signals are boosted for better coverage. 4. Passive DAS / Leaky Coaxial Cable Network: In the downlink direction, the amplified signals from the BDAs are distributed uniformly using a passive Distributed Antenna System (DAS) or a leaky coaxial cable network. This helps extend the signal reach where it couldn't reach directly. 5. Mobile Stations (MS): These are the devices used by the police, fire services, or other authorized personnel to communicate within the system. The uplink signals from MS are received by the DAS/Leaky Cable network and connected to the BDAs via RF feeder cables..

6 . Interfacing RF Feeder Cable: The RF feeder cable connects the DAS/Leaky Cable network to the BDAs, allowing the received uplink signals from the MS to be amplified by the BDAs before transmitting them back to the BTS via donor antennas. 7 . Redundancy and Combining: Two BDAs are planned for each system (TETRA, Police, Fire) to provide redundancy. The outputs of the BDAs are combined using a 2:1 hybrid combiner. Then, the combined signals from the three systems are further combined using a frequency-specific 3:1 combiner (Triplexer). 8 . Surge Arrester and DC Blocks: Surge arresters and DC blocks are installed in the system to protect the BDAs and BTS from high surges or voltage spikes..

9. Distributed Antenna System (DAS)/Leaky Cable: The combined signal (TETRA, Police, Fire) is connected to a passive DAS/Leaky Cable network. This network consists of interconnected antennas that distribute the radio signals throughout the tunnel or underground station, ensuring comprehensive and contiguous radio coverage for security communication services. 10. RF Slots and Cable Orientation: The LCX cable used in the system has RF slots cut on one side of the outer conductor, allowing the signal to be emitted mainly on that side. To ensure correct orientation, the non-signal side of the cable has an indicator strip, and installation should be done with the non-striped side facing the desired direction of signal propagation. To avoid interference, the non-signal side of the cable should be kept at least 10cm away from any wall or RF reflective surface. 11. Cable Clamps: Clamps are installed approximately 1 meter apart along the LCX cable to secure and support its installation..

Maintenance – Preventive. Preventive maintenance is scheduled maintenance performed to prevent equipment failure and extend its lifespan. It improves system reliability, decreases downtime, reduces replacement costs, and prevents deterioration through regular inspections and repairs. The ideal preventive maintenance program would prevent all equipment failure before it occurs. • Protect assets and prolong the useful life of production equipment • Improve system reliability • Decrease cost of replacement • Decreases system downtime • Reduce injury.

Maintenance – List of passive components. • Surge Arrestors • Combiners 2:1 & 3:1 • Power Splitters • Directional Couplers • RF coaxial cable/ Jumper cables • RF cable connectors • Indoor Omni Antenna • DC Block • Leaky Coaxial cable.

Preventive Maintenance for Passive DAS. • Regular inspection for Physical damage of Passive components • RF cable damage and excessive bending • Measurement of VSWR & return loss of the feeder system • Verify the connections , grounding and tapping of total DAS system • Check for the obstructions in front of the antennas • Check out for worn out labels and replace..

Preventive Maintenance for LCX Cable system. • Regular inspection for Physical damage of LCX cable • LCX cable damage and excessive bending • Measurement of VSWR & return loss of the feeder system • Verify the connections, DC Blocks, grounding, weather proofing of connectors, etc. • Check the condition of LCX supporting clamps and excessive sagging of cable • Check for the obstructions in front of the LCX cable • Check out for worn out labels and replace..

Maintenance – Corrective procedure. Corrective maintenance is performed to identify, isolate, and fix faults in equipment or systems, restoring them to operational condition. For DAS, standard RF components with minimal failure rates may require component replacement as the primary corrective action. Major faults, their causes, and corrective procedures are addressed to ensure proper functioning..

Common Faults in DAS. • Feeder and Connector damage • Splitter/Coupler faults • Combiner faults • Antenna damage or faults • Water leak in to the feeder.

Performance issues in DAS / LCX. • Poor or No coverage issues. • Call drop issues/bad quality • High drop calls/One way speech/Poor voice quality. • Call connectivity issues/Error in connection. • Data connectivity failure.

Troubleshooting. a) For poor or no coverage issues: Check connections, look for damage or malfunction in components, test VSWR, and verify power supply. Isolate problematic areas and troubleshoot combiners. b) Repeat the same steps as above for poor or no coverage issues, but also cross-check with the schematic and analyze back born power. c) For call drop/bad call quality: Check connections, isolate no coverage areas, analyze RF parameters, optimize as needed, and test VSWR. d) For voice breaking/one-way speech/poor voice quality: Follow the same steps as in (c) and also check for interference and address C/I, SNIR, and handover-related issues..

e) For call connectivity issues/error in connection: Check connections, isolate no coverage areas, analyze RF parameters, optimize as needed, and test VSWR. f) For data connectivity failure: Repeat the same steps as in (e) for call connectivity issues..

VSWR Test procedure. The recommended test equipment for VSWR testing is the Anritsu 331D Site Master along with its standard accessories. The VSWR test is performed to assess the quality and proper installation of passive components. If any branch or components fail to meet the prescribed standards, they should be replaced or rectified before commissioning. The Site Master/Site Analyzer is used for VSWR testing, and the test procedure involves calibration, connecting the cable, selecting SWR mode, locating faults using DTF mode, and ensuring proper termination and frequency selection. The equipment can also be used for RF power measurement. For testing DAS active equipment, EMS software and a power meter are utilized. Pre-commissioning sample test formats are provided for recording the test results..

VSWR Test Equipments. Test equipments: Site Master Calibration Tool Jumper cable.