User`s guide

Radio Signal Propagation
C-3
Figure C-2: Attenuation of an RF signal
P
in
is the incident power level before attenuation
P
out
is the output power level after attenuation
Attenuation is expressed in dB as follows:
P
dB
= -10 x Log
(P
out
/P
in
)
For example: If, due to attenuation, half the power
is lost (P
out
/P
in
= 1/2),
attenuation in dB is -10 x Log (1/2) = 3
dB
Path Loss
Loss of power of an RF signal traveling (propagating) through
space. It is expressed in dB. Path loss depends on:
♦ The distance between transmitting and receiving
antennas
♦ Line of sight clearance between the receiving and
transmitting antennas
♦ Antenna height
Free Space Loss
Attenuation of the electromagnetic wave while propagating
through space. This attenuation is calculated using the
following formula:
Free space loss = 32.4 + 20xLog(F
MHz
) + 20xLog(R
Km
)
F is the RF frequency expressed in MHz.