Engineering Tutorials

Microwave RF communication is estimated for rain and frequency. Each maps the world into “rain climate regions”. Based on the region, microwave links can be engineered to support any desired availability. The intersection of the radio margin line and the rain zone line is the distance that can be achieved with 99.999% availability . Except in extreme conditions, attenuation (weakening of the signal) due to rain does not require serious consideration for frequencies up to the range of 6 or 8 GHz. When microwave frequencies are at 11 or 12 GHz or above, attenuation due to rain becomes much more of a concern, especially in areas where rainfall is of high density and long duration. If this is the case, shorter paths may be required .

The systems discussed in this guide operate at frequencies below 6 GHz, so rain is not a concern.

In most cases, the effects of fog are considered to be much the same as rain. However, fog can adversely affect the radio link when it is accompanied by atmospheric conditions such as temperature inversion, or very still air accompanied by stratification. Temperature inversion can negate clearances, and still air along with stratification can cause severe refractive or reflective conditions, with unpredictable results. Temperature inversions and stratification can also cause ducting, which may increase the potential for interference between systems that do not normally interfere with each other. Where these conditions exist, Cisco recommends shorter paths and adequate clearances .