Campbell Manufacturing RF400 Manual De Usuario
Appendix H. Distance vs. Antenna Gain, Terrain, and Other Factors
H-6
Here is a table which gives calculated path loss (Lp) values at 900 MHz for the
2
2
nd
, 3
rd
, and 4
th
powers of distance; the equations (for 915 MHz) are:
Lp (2
nd
power) = 95.8 + 20
× log ( d ) dB
(d in miles)
Lp (3
rd
power) = 95.8 + 30
× log ( d ) dB
(d in miles)
Lp (4
th
power) = 95.8 + 40
× log ( d ) dB
(d in miles)
Example calculated Lp values (in dB)
TABLE H-1. 900 MHz Distance vs. Path Loss (Lp in dB) per Three Path Types
Path Type
2 mi.
4 mi.
6 mi.
8 mi.
10 mi.
14 mi.
18 mi.
22 mi.
26 mi.
30 mi.
2
nd
power
102
108
111
114
116
119
121
123
124
125
3
rd
power
105
114
119
123
126
130
133
136
138
140
4
th
power
108
120
127
132
136
142
146
149
152
155
The following table helps select a Path Type in the above “Distance vs. Path
Loss” table to best fit your situation.
Loss” table to best fit your situation.
TABLE H-2. Path Type vs. Path
Characteristics Selector
Path Type
Path Characteristics
2
nd
power
Mountaintop to mountaintop
or Tall antenna towers
Line-of-sight
or Tall antenna towers
Line-of-sight
3
rd
power
Dominantly line-of-sight
Low antenna heights
Some trees
Low antenna heights
Some trees
4
th
power
At water’s edge (very reflective)
Across field of grain (reflective)
Lots of Trees (absorptive)
Across field of grain (reflective)
Lots of Trees (absorptive)
Examples
Some examples will help illustrate the tradeoffs in a link analysis. These
examples will all use the RF400 900 MHz radio, and will use –107 dBm as the
required power level at the radio receiver. This is 3 dB higher than the quoted
sensitivity of –110 dBm, which will give us a 3 dB margin.
examples will all use the RF400 900 MHz radio, and will use –107 dBm as the
required power level at the radio receiver. This is 3 dB higher than the quoted
sensitivity of –110 dBm, which will give us a 3 dB margin.
Here’s the equation we will use, from the first page:
Pt - Lt + Gt - Lp + Gr - Lr = Pr
Example #1
Antenex FG9023 antennas on each end, 20’ of LMR195 cable on one end, 10’
of LMR195 on the other end, antennas at 10’ height, fairly open terrain with a
few trees. How far can I go?
of LMR195 on the other end, antennas at 10’ height, fairly open terrain with a
few trees. How far can I go?
Pt = 20 dBm
Lt = 20’ x (11.1 dB/100 ft) = 2.22 dB
Gt = Gr = 3 dBd = 5.15 dBi
Lr = 10’ x (11.1 dB/100 ft) = 1.11 dB
Lt = 20’ x (11.1 dB/100 ft) = 2.22 dB
Gt = Gr = 3 dBd = 5.15 dBi
Lr = 10’ x (11.1 dB/100 ft) = 1.11 dB