User's Manual Part 1
Release8PlanningGuide
Issue2,November2007 Draft5forRegulatoryReview 130
Tx
power
T
x antenna
gain
Tx
cable
loss
Rx antenna
gain
Rx
cable
loss
Rx
signal
level
Transmitter
or Amplifier
receiver
or amplifier
distance
free space signal
transmitter
or amplifier
Figure 31: Determinants in Rx signal level
Rx signal level is calculated as follows:
Rx signal level dB = Tx power − Tx cable loss + Tx antenna
gain
− free space path loss
+ Rx antenna gain − Rx cable loss
NOTE:
This Rx signal level calculation presumes that a clear line of sight is established
between the transmitter and receiver and that no objects encroach in the Fresnel
zone.
12.1.4 CalculatingFadeMargin
Free space path loss is a major determinant in Rx (received) signal level. Rx signal level,
in turn, is a major factor in the system operating margin (fade margin), which is calculated
as follows:
system operating margin (fade margin) dB =Rx signal level dB −
Rx sensitivity dB
Thus, fade margin is the difference between strength of the received signal and the
strength that the receiver requires for maintaining a reliable link. A higher fade margin is
characteristic of a more reliable link.