Afar AR24027, Руководство оператора

Страница: 75 / 100

AR24027 Operator’s Manual
6-10
F = 2400 (frequency in MHz)
D = total path length in km (d1 + d2).
Add the “d” value to the height of each obstruction plotted on the graph.
8. Determine ideal antenna height by drawing a line on the graph between the sites and across the
top of the obstruction heights. Note the elevation at each antenna site.
6.4.2 Receive Signal Strength Calculation
This section shows how to calculate the RSS level expected at the radio and to determine the
theoretical link margin. The AFAR “RF Link Budget Calculator”, available in the CD or at the
website, that performs all of these computations.
1. Determine free-space path loss, using either the following formula or the graph of Figure 6.3.
−
L
=
C
+
20log(D)
+
20 log(F)
Where:
(for US units)
 -L = loss in dB
C = 36.6 for US units
D = path length in miles
F = 2400 (frequency in MHz)
(or for metric units)
 -L = loss in dB
C = 32.5 for metric units
D = path length in km
F = 2400 (frequency in MHz)
For example, for a distance of 10 miles
) 2400 log( 20 ) 10 log( 20 6 . 36
+ + = −
L
dB L 124
= −