The climate factor used in the reliability calculation can be entered directly or computed from average annual temperature information.

Lenkurt suggests the following values:

• .5 for gulf coast or similar hot, humid areas.
• .25 for normal interior temperate or northern areas.
• .125 for mountainous or very dry areas.

In the legacy microwave reliability calculation, the climate factor can be computed using the formula (from Roelofs):

B = T/50 x 3/12

where:

• T is the average annual temperature in degrees Fahrenheit.

If you calculate the value as described above, the value will be marked “CALC” on printed output, and the temperature will be included. However, if you enter any value directly, the value will be marked “SPEC” (for specified).

In the two-way microwave link budget, this b term is included in the Undp calculation as the term (T_s / T_ref),

where:

• T_s is the number of seconds in the heavy fading season = 8 x 10⁶ x T/50
• T_ref is the number of seconds in a year.
• T is the average annual temperature, in degrees Fahrenheit; 35 < T < 75.

Thus, (T_s / T_ref) = (8 x 10⁶ x T/50) / (365.25 x 86400) = T/50 x 0.254.

References:

1. Engineering Considerations for Microwave Communications Systems, 1975, GTE Lenkurt Incorporated.
2. Roelofs, Stan, “Fade Margin Requirements for Microwave Systems”, Microwave Reference Guide, 1986, Motorola.
3. ANSI/TIA-10-A-2023. TIA Standard: Interference Criteria for Microwave Systems.  April 2023.