Propagation Degrades
Last updated
Last updated
Attenuation in free space: signal gets weaker as it travels over long distances.
Radio signal spreads out – free space loss.
Refraction and absorption in the atmosphere.
Frequency dependent!
Obstacles can weaken the signal through absorption or reflection.
Part of the signal is redirected.
Multi-path effects: multiple copies of the signal interfere with each other.
Mobility: moving the receiver causes another form of self interference.
Big change in signal strength.
Speed of EM signals depends on the density of the material.
Vacuum: 3 x 108m/sec.
Denser: slower.
Density is captured by refractive index.
Explains “bending” of signals in some environments.
E.g. sky wave propagation.
But also local, small scale differences in the air.
Caused by agitation of the electrons.
Function of temperature.
Affects electronic devices and transmission media.
Result of mixing signals.
Picking up other signals.
E.g. from other source-destination pairs.
Irregular pulses of high amplitude and short duration.
Harder to deal with.
Very serious at specific frequencies, e.g. water vapor (22 GHz) and oxygen (60 GHz).
Obviously objects also absorb energy.
