Quad Cable Communication System Overview

Quad Cable Based Control Communication System

• Indian Railways uses optical fiber cable (OFC) and six quad jelly-filled cables on important routes. On less important routes, only quad cables are used.
• Control communication on OFC uses STM-1/IP-MPLS router and P.D.MUX equipment at stations. Block circuits, emergency sockets, and level crossing gates are communicated via quad cable.
• If OFC cable installation is pending, control and block communication relies solely on the quad cable.
• The Amplifier-Equaliser system allows communication at each station without needing to load the quad cable.
• Each station needs amplifier-equaliser equipment to compensate for signal losses across the VF band.
• The system includes cable termination, distribution, and monitoring panels, 'U' link panels, equaliser amplifiers, and VF transformer panels with decoder and other printed circuit boards (PCBs).

Electrical Parameters

• Input impedance for the VF amplifier is 470 ohms ±10%.
• Nominal gain at 1kHz is 20 dB ±1 dB.
• Frequency from 300 Hz to 3.4 kHz has a ±3 dB flat response.
• Input signal minimum is -20 dBm, and output is 0 dBm with amplifier gain.
• Cross-talk level between adjacent quads must be better than -60dB at 1kHz.
• Equaliser response must vary between 0 dB and 12 dB for 300 Hz to 3.4 kHz with no distortion (3%) at maximum gain.

Power Supply Requirements

• The Amplifier-Equaliser equipment typically operates at 230V AC, with a variation range of 160V to 270V.
• Systems can switch to solar power automatically.
• The power supply is duplicated, including batteries, with short-circuit protection and voltage protection.
• The system allows for by-passing of way station equipment if battery voltage drops below the required threshold level.
• Two low-maintenance 12V batteries with a capacity of 40Ah are required, sufficient for 72 hours of operation.

Intercom Facility

• Stations have 8-way intercom with dialing functionality.
• Separate cards are provided for 8-way intercom for each station.
• Extension up to 300 Ohms loop resistance is possible.
• Intercom circuit design allows for all subscribers to communicate without interrupting the controller.

Remote Monitoring Facility

• The system allows for remote monitoring and fault localization.
• Separate monitoring is provided for sectional, deputy and S&T control circuits.
• Remote monitoring allows functions such as disconnecting circuit cards or cutting buffers, changing battery, monitoring voltages, and status (e.g., AC fuse).
• The Remote Card automatically sends fuse failure alerts with its identity to the test room.
• Authorization codes, password, or keys are needed for disabling/enabling command codes to prevent unauthorized activity.

Earthing

• All non-current carrying metal parts of the amplifier/equaliser and the quad cable sheath are bonded together and grounded.

Maintenance Schedule

• A detailed schedule for equipment maintenance is provided, listing frequencies and responsibilities for various technicians like Telecom Technician, Junior Engineer, and Senior Section Engineers.
• This includes checking voltage, card positioning, circuit functioning, and line-up for the equipment and Batteries.