RADIUS
Product
Description
PDR 121
iom_pdr121_04_r02.doc
Rev 02
Page 39 (67)
11.2 Fade Margin
Fade Margin is an expression for how much margin - in dB - there is between the received signal
strength level and the receiver sensitivity of the radio.
The figure below describes the term fade margin. Site A is transmitting with 33dBm (2W) power.
After the distance to site B, the signal level has dropped to –100 dBm. This gives a margin of –10
dBm since the receiver sensitivity of the radio at site B is -110 dBm.
Figure 10. Fade Margin
In very noisy environments, the level of the noise floor can be higher than the receiver sensitivity.
(For example greater than -110 dBm in the above example). In this case, it does not help to
increase the receiver sensitivity or using a higher gain-receiving antenna. The only solution if the
source of the noise cannot be eliminated is then to increase the power of the transmission so that
signal strength at the receiving radio is higher than the noise. However, in some cases, moving the
receiving antenna can reduce the noise impact.
Site A
Site B
Fade Margin
(10dB)
-100
-110
Noise floor (average)
-130
0
33 (2W)
dBm
PDR121
Receiver sensitivity
Received Signal
Strength @ Site B
Transmitted Signal
Strength @ Site A
Distance