A crucial factor in the success or failure of a communications system is how
much power from the transmitter actually reaches the receiver. Many different
ways that EM waves can be affected have been discussed, including reflection,
diffraction, and scattering. These different effects can be combined and
described by what are known as path loss calculations. Path loss calculations
determine how much power is lost along the communications path.
Free-space loss (FSL) is the signal attenuation that would result if all
absorbing, diffracting, obstructing, refracting, scattering, and reflecting
influences were sufficiently removed so as to have no effect on propagation.
The formula is as follows:

FSL (in dB) = 20 log10(f) + 20 log10(d) + 36.6
Every time the distance from the transmitter to the receiver is doubled, the
signal level is lowered (or increased) by 6 dB. Also, for each frequency, there
is a series of wavelengths, where energy will escape out of the transmission
line and enter the surrounding space. This is called the launch effect. The
launch effect typically occurs at multiples of half-wavelengths of the signal.
This is illustrated in Figure
.
Use the path loss calculator in the interactive activity to gain familiarity
with this calculation. Enter any two of the values and the third one will be
calculated. Then, use the simulator in the second interactive activity to see
how this can affect WLAN communications.