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

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)

H-4

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