Problems Associated with Long Path Communication Links in Tropical Areas

Southern Railway have collected extensive data on microwave propagation over their 2000 KM net-work for over five years. The main problem of long path communication link is the occurrence of momentary deep fades of 10 to 40 dB for very short duration of 1 to 2 seconds. These dropouts. account for 80% of the total severe fading and about 60% of the total outage occur. in pre-summer months viz., February, March and April. The probability occurrence of deep fades increases very rapidly with distance and a computerised study indicate. that it is proportional to (Distance)10. Comparative study of Space Diversity and Frequency Diversity for long path indicates that Space Diversity reduces the outage time by 50% whereas Frequency Diversity wih even a small frequency separation of 1% reduces the outage by as much as 90%. Frequency Diversity, therefore, appears to be definitely more suited to tropical areas subjected to heavy momentary outages tban Space Diversity.