Question
Thu January 10, 2013 By: Vidhi Mehta

What is the difference between attenuation and fading

Expert Reply
Fri January 11, 2013
Attenuation::
Attenuation (fading) of an RF signal is defined as follows:

Pin is the incident power level at the attenuator input
Pout is the output power level at the attenuator output
Attenuation is expressed in dB as follows:PdB = 10 x Log (Pout/Pin)
For example: If, due to attenuation, half the power is lost (Pout/Pin = 2),
Attenuation is caused by different factors.(one of them is fading) like:
1.Path Loss:
Path loss is the loss of power of an RF signal travelling (propagating) through space. It is expressed
in dB. Path loss depends on:
1.The distance between transmitting and receiving antennas.
2.Line of sight clearance between the receiving and transmitting antennas.
3.Antenna height.
2.Free Space Loss:
Attenuation of the electromagnetic wave while propagating through space.
3.Antenna Characteristics

4.System Characteristics
1.Receiver Sensitivity
The minimum RF signal power level required at the input of a receiver for certain performance (e.g.
BER).
2. EIRP (Effective Isotropic Radiated Power)
The antenna transmitted power. Equal to the transmitted output power minus cable loss plus the
transmitting antenna gain.
5.Signal Fading
Fading of the RF signal is caused by several factors:
1.Multipath
The transmitted signal arrives at the receiver from different directions, with different path lengths,
attenuation and delays. The summed signal at the receiver may result in an attenuated signal.

2.Bad Line of Sight
An optical line of sight exists if an imaginary straight line can connect the antennas on either side
of the link.
Radio wave clear line of sight exists if a certain area around the optical line of sight (Fresnel zone)
is clear of obstacles. A bad line of sight exists if the first Fresnel zone is obscured.
3.Link Budget Calculations
4.Weather conditions (Rain, wind, etc.)
eg,Wind may cause fading due to antenna motion.
5.Interference
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