Exalt Communications, Inc.
r-series
Installation and Management Manual
5000007 (ETSI)
74
2007-02-12 (draft)
Insufficient Link Margin
Ideally, the link was designed with enough link margin (fade margin) to allow for multipath
propagation and atmospheric fading and still remain reliable. In some cases, link margin is
compromised by economic factors, such as using low-cost RF cabling or lower-cost antennas
that have less gain or deficient performance compared to higher cost transmission system
components. In some cases, there may be antenna size restrictions that forced the design to not
have the desired amount of link margin.
If the link was designed with poor link margin, there are likely many cases of bit errors and
outages. The antenna system and transmission line can be upgraded to help reduce this. If the
link design was installed with sufficient margin, but RSL is reduced, the remaining link margin
may no longer be enough to maintain a reliable link. The causes of RSL reduction were
previously described, but are usually due to new path obstruction(s) or antenna misalignment due
to wind or mechanical factors. The antenna height or location can be changed to overcome new
obstructions. Realignment of the antenna, and/or improvement to mechanical structures can help
overcome antenna misalignment.
Moisture in the Transmission System
If the connectors on cables and antennas and egress junctions are not properly weatherproofed,
moisture can get into the transmission system and cause significant error conditions and erratic
performance. In many cases, the transmission system must be replaced. A VSWR meter is one
means to identify such issues. Physical inspection can be helpful, and if changes to the
weatherproofing occur (such as cracks), the weatherproofing must be replaced before it leaks.