User Manual

Appendix B. Distance vs. Antenna Gain, Terrain, and Other Factors

The following table helps select a Path Type in the above “Distance vs. Path

Loss” table to best fit your situation.

TABLE B-8. Path Type vs. Path

Characteristics Selector

Path Type Path Characteristics

power Mountaintop to mountaintop

or Tall antenna towers

Line of sight

power Dominantly line of sight

Low antenna heights

Some trees

power At water’s edge (very reflective)

Across field of grain (reflective)

Lots of Trees (absorptive)

B.4 Examples

Some examples will help illustrate the trade-offs in a link analysis. These

examples will all use the RF401A-series 900 MHz radio at maximum

transmitter power, and will use –106 dBm as the required power level at the

radio receiver. This is 3 dB higher than the quoted sensitivity of –109 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

Solved for Lp:

Lp = Pt – Lt + Gt + Gr – Lr – Pr

Example #1

Antenex FG9023 antennas on each end, 20 ft of LMR195 cable on one end,

10 ft of LMR195 on the other end, antennas at 10 ft height, fairly open terrain

with a few trees. How far can I go?

Pt = 24 dBm

Lt = 20 ft • (11.1 dB/100 ft) = 2.22 dB

Gt = Gr = 3 dBd = 5.15 dBi

Lr = 10 ft • (11.1 dB/100 ft) = 1.11 dB

Use –106 dBm for Pr

Lp = 24 – 2.22+ 5.15 + 5.15 – 1.11– (–106) = 137 dB

Use the 3

to 4

power tables: Range from ~10 (4

power) to ~24 (3

power)

miles

B-7