Campbell RF401A Series, Инструкция по эксплуатации

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Appendix B. Distance vs. Antenna Gain, Terrain, and Other Factors
B-7
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 –109 dBm as the required power level at the
radio receiver.
Here’s the equation we will use, from Appendix B.2.2 , Link Budget
(p. B-2)
:
Ptx – Ltx + Gtx – Lpath + Grx – Lrx = Prx
As previously stated, the amount by which Prx exceeds the receiver’s
sensitivity is the fade margin. Therefore, in this example:
Fade margin = Prx – (–109 dBm)
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?
Ptx = 24 dBm
Ltx = 20 ft • (11.1 dB/100 ft) = 2.22 dB
Gtx = Grx = 3 dBd = 5.15 dBi
Lrx = 10 ft • (11.1 dB/100 ft) = 1.11 dB
From Appendix B.3 , Real World Distance Estimates
(p. B-5)
, we know:
Lpath (2-Ray) = 120 – 20log (h
tx
• h
rx
) + 40Log (d) (h in met re s, d in km)
Lpath (2-Ray) = 120 – 20log (3.05 • 3.05) + 40Log (1.609 • d in mi)
Lpath (2-Ray) = 120 – 19.37 + 40Log (1.609 • d in mi)
Lpath (2-Ray) = 100.36 + 40Log (1.609 • d in mi)
Using the above equation to calculate Lpath at different distances, gives:
TABLE B-8. Lpath vs. Distance for 2-Ray Propagation Model in Example #1
Distance 2 mi. 4 mi. 6 mi. 8 mi. 10 mi. 14 mi. 18 mi. 22 mi. 26 mi. 30 mi.
Lpath 121 133 140 145 149 155 159 162 165 168
Now we will calculate the fade margin for each distance:
Fade margin = Prx – (–109 dBm)
Fade margin = Ptx – Ltx + Gtx – Lpath + Grx – Lrx + 109 dBM
Fade margin = 24 – 2.22 + 5.15 – Lpath +5.15 – 1.11 + 109
Fade margin = 140 – Lpath