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Official Documentation

Scenario 2 - Scheduled Maintenance

Duration: 20-30 min

Difficulty: Beginner

Mission Type: Tutorial

Learning Objectives

By the end of this scenario, you will be able to:

  • Execute a safe RF equipment shutdown sequence
  • Understand why sequence order matters for personnel safety
  • Command antenna positioning for maintenance access
  • Restore a satellite link following proper power-up procedures
  • Verify link acquisition using beacon signals

Mission Briefing

It’s your second day at North Atlantic Teleport Services. The maintenance crew needs to perform work on the TIDEMARK-1 antenna feed assembly - specifically replacing a waveguide flange gasket. This requires taking the link offline, moving the antenna to maintenance position for safe access, then restoring full service after the maintenance window completes.

This is your first time actually controlling the equipment. Charlie Brooks will provide all frequency values and configuration settings - you just need to execute the procedures in the correct sequence.

Critical Mission Context:

  • Maintenance Required: Waveguide flange gasket replacement on antenna feed
  • Safety Priority: RF radiation can harm personnel - proper shutdown sequence is mandatory
  • Service Impact: TIDEMARK-1 will be offline for approximately 15 minutes
  • Customer Notification: SeaLink has been notified of the maintenance window
  • Your Role: Execute power-down and recovery procedures under Charlie’s supervision

Who’s Supervising:

  • Charlie Brooks: Senior operator ensuring you follow proper procedures

RF Safety Brief

Hazard Overview

The transmit chain at VT-01 operates at power levels capable of causing serious injury. The High Power Amplifier (HPA) is capable of outputs up to several hundred watts of RF energy at C-band frequencies (5.85-6.725 GHz). At these power levels:

  • Thermal burns can occur from direct exposure to the antenna feed
  • RF radiation exposure can cause tissue heating, particularly dangerous to eyes and reproductive organs
  • Induced currents in metal objects near the feed can cause burns on contact

Exposure Limits

NATS follows OSHA and FCC RF exposure guidelines:

  • Occupational limit at C-band: 10 mW/cm² averaged over 6 minutes
  • Exclusion zone: No personnel within 3 meters of feed horn while transmitting
  • Time-weighted exposure: Even brief exposures at high power can exceed safe limits

Required Procedures

Before any personnel approach the antenna feed assembly:

  1. Transmit chain must be fully de-energized - HPA output disabled AND powered off
  2. BUC must be muted - Prevents any residual RF output
  3. Lockout/Tagout - Control room maintains positive control of transmit enable
  4. Verbal confirmation - Two-way radio confirmation that RF is secured before crew approaches

Your Responsibility

As the operator on console, you are the last line of defense. Never re-enable transmit equipment while maintenance personnel are in the exclusion zone. If in doubt, verify crew position before any transmit chain changes.

Background: The RF Signal Chain

Understanding the equipment you’re controlling helps you understand why sequence matters.

Modem → BUC → HPA → Antenna → Satellite
  • BUC (Block Upconverter): Converts the intermediate frequency (IF) signal from the modem to the RF frequency for transmission. Outputs milliwatts of power.
  • HPA (High Power Amplifier): Amplifies the RF signal to hundreds of watts for transmission to the satellite. This is the dangerous component.

The HPA is downstream from the BUC, so even if the BUC is muted, an enabled HPA could amplify noise or spurious signals. Always disable the HPA first when shutting down.

Satellite → Antenna → LNB → Receiver/Modem
  • LNB (Low Noise Block): Amplifies the weak satellite signal and converts it from RF to IF for the receiver. Contains sensitive electronics that need thermal stabilization.

The LNB doesn’t pose a safety hazard, but it needs time to thermally stabilize after power-up before measurements are accurate.

Why Sequence Matters

Shutdown sequence (HPA → BUC → LNB → Antenna):

  • Disable highest-power components first to eliminate hazard quickly
  • Keep antenna pointed at satellite until RF is secured (maintains link until last moment)
  • Move antenna only after all RF is off

Startup sequence (Antenna → LNB → verify → BUC → HPA):

  • Point antenna before powering receive chain (ensures signal path exists)
  • Verify beacon reception before enabling transmit (confirms pointing is correct)
  • Enable low-power stages before high-power (BUC before HPA)

Equipment Reference

Antenna Control Unit (ACU)

The ACU commands antenna position and tracking mode:

ModeDescription
Program TrackAntenna follows calculated satellite position based on orbital data
MaintenanceMoves antenna to stow position (Az 0°, El 5°) for safe access

The maintenance position (elevation 5°) tilts the dish low enough for crew access to the feed assembly while keeping it above horizon obstructions.

LNB Parameters for TIDEMARK-1

ParameterValuePurpose
LO Frequency5,250 MHzLocal oscillator for frequency conversion
Gain60 dBSignal amplification
Thermal Stabilization~60 secondsTime for electronics to reach stable operating temperature

IF Frequency Calculation: The spectrum analyzer displays IF (intermediate frequency), not RF. For C-band with a 5,250 MHz LO:

  • TIDEMARK-1 beacon transmits at 4,175.5 MHz RF
  • IF = LO - RF = 5,250 - 4,175.5 = 1,074.5 MHz IF

Antenna Position for TIDEMARK-1

ParameterValue
Azimuth161.8°
Elevation34.2°
Tracking ModeProgram Track

Procedure Overview

Pre-Maintenance Preparation

Before any equipment changes:

  1. Open Mission Brief - Review the maintenance documentation
  2. Safety Briefing - Acknowledge RF safety procedures

Power-Down Sequence

The correct order is critical for safety:

  1. Disable HPA Output - Stop RF output from the amplifier
  2. Power Off HPA - Completely power down the High Power Amplifier
  3. Mute BUC - Mute the Block Upconverter RF output
  4. Power Down LNB - Shutdown receive path
  5. Move Antenna to Maintenance Position - Command to Az 0°, El 5° for feed access

Power-Up Sequence

Reverse order with verification steps:

  1. Repoint Antenna - Return to operational position (Az 161.8°, El 34.2°) using program-track mode
  2. Restore LNB - Power on with LO 5,250 MHz, Gain 60 dB
  3. Wait for Thermal Stabilization - LNB indicator will turn green when ready
  4. Verify Beacon - Confirm TIDEMARK-1 beacon at 4,175.5 MHz RF (1,074.5 MHz IF)
  5. Unmute BUC - Enable RF path
  6. Power On HPA - Power up the High Power Amplifier
  7. Enable HPA Output - Enable output to restore full service

Success Criteria

  • All safety procedures followed in correct sequence
  • Equipment restored to operational status
  • Beacon visible on spectrum analyzer at 1,074.5 MHz IF
  • Link restored within authorized maintenance window