Dealing With Adjacent Satellite Interference (ASI)

Adjacent Satellite Interference (ASI), GEO Ku, Ka or C-Band

Objective: Restore link quality when your antenna is picking up energy from one or more neighbour satellites in the arc.

Typical Symptoms

• Degraded C/(N+I) on specific downlink carriers, worst when:
  • Weather is clear (rules out rain fade)
  • Neighbour satellites are heavily loaded
• Problems concentrate on small dishes (45-65 cm) and mobile VSATs
• QoS drops when a new adjacent satellite enters service or turns on carriers in co-frequency, co-coverage, co-polarization

Immediate Actions (0-15 Min)

Confirm it's downlink ASI, not local noise:

• Compare multiple terminals on different satellites from the same site
• If only one orbital slot is affected, suspect ASI

Check dish pointing quickly:

• Use available pointing or quality metrics (modem Eb/N0, STB bar)
• If you can safely adjust, try fine azimuth or elevation tweaks of ±0.2-0.3° while watching C/N (don't over-rotate)

Escalate to satellite operator:

• Ask if there were recent activations or power changes on adjacent satellites

Investigation (15-120 Min)

Step 1: Characterize the interference

• Capture before and after spectra around the affected carrier
• Identify whether you see:
  • A clear adjacent carrier bleeding in
  • A broad noise skirt from a saturated carrier on a neighbour

Step 2: Dish and RF checks

Verify:

• Antenna size and feed type against link budget assumptions
• Mounting hardware (no loose clamps or bent mounts)
• RF chain losses and LNB config

For installations using sub-1 m dishes, note that beamwidth is wide enough that C/(N+I) is often dominated by ASI, especially with 2-3° orbital separation.

Step 3: Coordination with sat operator

Request:

• EIRP maps of your satellite and adjacent satellites
• Coordination limits and any known hot-spots in your region
• Confirmation whether you're operating near co-frequency, co-polarization beams from neighbours

Mitigation and Recovery

Tactical fixes:

• Slightly de-point the antenna toward the desired satellite to reduce gain toward the stronger interferer (as advised by the sat operator)
• If available, switch to a larger dish or higher-gain antenna, which improves on-axis versus off-axis discrimination and boosts C/(N+I)
• If you have dual-satellite options for the same service, move affected traffic to a less crowded orbital slot

Network-level actions:

Work with the sat operator to:

• Move sensitive carriers to different transponders or frequencies further from the neighbour's high-power carriers
• Adjust power and roll-off to meet coordination limits while maintaining service

Prevention

During network design and procurement:

• Include explicit ASI margin in link budgets for small dishes at 2-3° slot spacing
• Select antenna sizes and feed patterns based on documented C/(N+I) versus dish size and orbital separation tables or tools

Operationally:

• Maintain a database of adjacent satellite plans (current and future) in each coverage region and track changes
• Standardize installation best practices and post-install verification (spectrum analyzer or equivalent)