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Appendix H. Distance vs. Antenna Gain, Terrain, and Other Factors
H-7
Use –107 dBm for Pr, solve for Lp: Lp = 135 dB
Use the 3
rd
to 4
th
power tables: Range from ~9 (4
th
power) to ~22 (3
rd
power)
miles
Example #2
Base has MaxRad BMOY8905 Yagi, with 50’ of LMR195 cable on a 30’
tower, also a lightening protection device with a VSWR of 1:1.75; remote also
has a MaxRad BMOY8905 Yagi with 5’ of LMR195 cable on a 4’ pole.
Terrain is mostly flat, with sagebrush. How far can I go?
Pt = 20 dBm
Lt = 50’ x (11.1 dB/100 ft) = 5.55 dB
Gt = 9 dBd = 11.15 dBi
Lr = 5’ x (11.1 dB/100 ft) = .55 dB
Gr = 9 dBd = 11.15 dBi
Need to include the loss from the surge arrestor: VSWR of 1:1.75 = .34 dB loss
Use –107 dBm for Pr, solve for Lp: Lp = 143 dB
Use the 3
rd
to 4
th
power tables: Range from ~14 (4
th
power) to 30+ (3
rd
power)
miles
Example #3
You need to run 125’ of cable for the transmitter:
How much loss if I use LMR195 cable? 125’ x (11.1 dB/100’) = 13.9 dB
How much loss if I use LMR400 cable? 125’ x (3.9 dB/100’) = 4.9 dB
If I am using path loss from the 2
nd
power table, and operating fine at 8 miles
with LMR195 cable, how much more range could I expect if I use LMR400
cable (assuming similar terrain)?
13.9 dB – 4.9 dB => 9 dB more link margin
Loss at 8 miles: 114 dB; could tolerate 114 + 9 dB = 123 dB loss =>>> 22
miles (14 miles more)