MICROWAVE (MW) LINK DOWN – FULL GUIDE
[ MW LINK STRUCTURE ]
[ IDU ] ===== IF Cable ===== [ ODU ] )))) AIR (((([ ODU ] ===== IF Cable ===== [ IDU ]
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[ COMMON ALARMS ]
– LOS (Loss of Signal)
– LOF (Loss of Frame)
– RSL LOW
– HIGH BER
– LINK DOWN
– NO FAR END
– RF MUTED
– ODU NOT CONNECTED
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[ ROOT CAUSES OF MW LINK DOWN ]
1. WEATHER (RAIN FADE)
– Heavy rain absorbs RF signal
– High frequency (18/23 GHz) more affected
RESULT:
→ RSL drop
→ BER increase
→ Link Down
2. ALIGNMENT ISSUE
– Antenna moved by wind
– Loose mounting
– Fresnel zone disturbance
RESULT:
→ Sudden RSL drop
→ Unstable link
3. POWER FAILURE
– IDU power OFF
– ODU no DC supply
– Rectifier/battery problem
RESULT:
→ Complete link down
4. HARDWARE FAULT
– ODU damaged
– IDU modem/card faulty
– SFP/port issue
RESULT:
→ No signal transmission
5. IF / RF CABLE PROBLEM
– IF cable cut/loose
– Connector damaged
– Water inside cable
RESULT:
→ Signal loss / intermittent link
6. INTERFERENCE
– Same frequency nearby
– External RF noise
RESULT:
→ High BER
→ Link flapping
7. CONFIGURATION MISMATCH
– Frequency mismatch
– Polarization mismatch (V/H)
– Wrong bandwidth / modulation
RESULT:
→ No link establishment
8. LOS (LINE OF SIGHT) BLOCKED
– New building / tower
– Tree growth
RESULT:
→ Weak or no signal
9. SOFTWARE ISSUE
– System hang
– Firmware bug
RESULT:
→ Link freeze / down
10. DESIGN LIMITATION
– Long distance link
– No fade margin
– No protection (1+0)
RESULT:
→ Link fails in stress condition
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[ TROUBLESHOOTING FLOW ]
STEP 1: CHECK POWER
– IDU ON?
– ODU getting -48V DC?
STEP 2: CHECK ALARM
– LOS / LOF / RSL LOW?
– ODU disconnected?
STEP 3: CHECK RSL VALUE
– Normal? → ~(-30 to -50 dBm depending on design)
– Too low? → Alignment / Rain / Cable issue
STEP 4: CHECK WEATHER
– Heavy rain? → Wait & monitor
STEP 5: CHECK FAR END
– Reachable via NMS?
– If NO → Far end power down
STEP 6: CHECK CABLE
– IF cable tight?
– Connector OK?
STEP 7: CHECK ALIGNMENT
– Re-align antenna using RSL
– Tight all bolts
STEP 8: CHECK CONFIGURATION
– Frequency same both sides?
– Polarization correct?
STEP 9: CHECK INTERFERENCE
– Spectrum scan
– Change frequency if needed
STEP 10: RESTART
– Reboot IDU/ODU
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[ QUICK FIELD DIAGNOSIS ]
IF → NO POWER
→ Check rectifier / DC
IF → RSL = 0 / VERY LOW
→ Alignment / ODU / Cable
IF → HIGH BER
→ Interference / Rain
IF → NO FAR END
→ Far end down / Config mismatch
IF → LINK FLAPPING
→ Interference / Alignment
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[ BEST PRACTICE ]
✔ Maintain proper alignment
✔ Use good quality cable
✔ Ensure LOS clear
✔ Keep proper fade margin
✔ Use protection (1+1 link)
✔ Regular preventive maintenance
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==================== END OF MW LINK DOWN GUIDE ====================
