User manual

Appendix A: Path Evaluation Information A-9
Moseley SL9003Q 602-12016 Revision G
a (terrain factor)
= 4 for smooth terrain.
= 1 for average terrain.
= 1/4 for mountainous, very rough, or very dry terrain.
Q. Line 18. Enter the Climate Factor.
b (climate factor)
= 1/2 for Gulf coast or similar hot, humid areas.
= 1/4 for normal interior temperate or northern regions.
= 1/8 for mountainous or very dry areas.
R. Line 19. Enter the minimum Annual Outage (from Table A-6).
S. Line 20. Enter the Reliability percentage (from Table A-6).
A.2.4 Path Availability and Reliability
For a given path, the system reliability is generally worked out on methods based on the work of
Barnett and Vigants. The presentation here has now been superseded by CCIR 338-6 that
establishes a slightly different reliability model. The new model is more difficult to use and, for
most purposes, yields very similar results. For mathematical convenience, we will use fractional
probability (per unit) rather than percentage probability, and will deal with the unavailability or
outage parameter, designated by the symbol U. The availability parameter, for which we use
the symbol A, is given by (1-U). Reliability, in percent, as commonly used in the microwave
community, is given by 100A, or 100(1-U).
Non-Diversity Annual Outages
Let U
ndp
be the non-diversity annual outage probability for a given path. We start with a term r,
defined by Barnett as follows: