Campbell RF401, Инструкция по эксплуатации, Страница: 90 / 130

Appendix H. Distance vs. Antenna Gain, Terrain, and Other Factors
H-4
CSI’s “COAX RPSMA-L” uses LMR-195 antenna cable. Cable loss is
proportional to length as the following table illustrates.
LMR-195 Cable Loss vs. Length @ 900 MHz
LENGTH
(ft.)
LOSS
(dB)
100 11.1
50 5.6
25 2.8
10 1.1
6 0.7
Antenna Gain
Antenna gain is specified either in dBi (decibels of gain relative to an isotropic
radiator) or in dBd (decibels of gain relative to a dipole). The relationship is:
dBi = dBd + 2.15
Some antennas that are FCC approved for use with the RF401 series are:
Mfg. Antenna Type Band Model CSI Item # dBd
Gain
dBi
Gain
Size
Astron Omni (1/2 wave) 900 MHz AXH900 RP SMA R 14204 0 2.15 6.75”
Antenex Collinear 900 MHz FG9023 14221 3 5.15 24”
MaxRad Yagi 900 MHz BMOY8905 14201 9 11.15 21.4”
LINX Omni (1/2 wave) 2.4 GHz ANT-2.4-CW-RCT-RP 16005 0 2.15 4.5”
MaxRad Enclosed Yagi 2.4 GHz WISP24015PTNF 16755 13 15.1 17”
Receiver Sensitivity
Receiver sensitivity is usually specified in dBm for a specific bit error rate
(BER). The transceiver module used in the RF401, RF411, RF430, or RF431
is specified at –110 dBm at ~10 -4 raw BER.
If the received signal strength is greater than the receiver sensitivity, a link can
be established. Any excess signal strength above the receiver sensitivity is
“link margin”, and is a very good thing; a minimum of 6 dB of link margin
should be sought.
Path Loss
We have combined in this section the normal “free space” path loss (only seen
in mountaintop to mountaintop scenarios) with loss due to ground reflections,
diffraction, leaf/forest absorption, etc. It is all loss!
A starting point is the “free space” path loss. Here are two equations for this:
Lp (dB) = 32.4 + 20 x log( f ) + 20 x log ( d ) dB (f in MHz, d in km)
Lp (dB) = 36.6 + 20 x log( f ) + 20 x log ( d ) dB (f in MHz, d in miles)