Propagation of Electromagnetic Waves II Video Lecture - Civil Engineering (CE)

the details of which are given in table
the degree of ionize
varies with the height the density of
atmosphere decreases with height at
great heights the solar radiation is
intense
but there are few molecules to be
ionized close to the earth even though
the molecular concentration is very high
the radiation intensity is low so that
the ionization is again low however at
some intermediate Heights there occurs a
peak of ionization density the INA
spheric layer acts as a reflector for a
certain range of frequencies three to
thirty megahertz electromagnetic waves
of frequencies higher than thirty
megahertz penetrate the I no sphere and
escape these phenomena are shown in the
figure the phenomenon of blending of e/m
waves so that they are diverted towards
the earth is similar to total internal
reflection in optics space wave another
mode of radio wave propagation is my
space waves a space wave travels in a
straight line from transmitting antenna
to the receiving antenna space waves are
used for line-of-sight hello s
communication as well as satellite
communication at frequencies about 40
megahertz communication is essentially
limited the line of sight paths at these
frequencies the antennas are relatively
similar and can be placed at heights of
many wavelengths about the ground
because of line-of-sight nature of
propagation direct waves get blocked at
some point by the curvature of the earth
as illustrated in Figure if the signal
is to be received beyond the horizon
then the receiving antenna must be high
enough to intercept the line-of-sight
waves
if the transmitting antenna is at a
height
Paige D then you can show that the
distance to the horizon DT is given as
DT equals to square root of 2 RH T where
R is the radius of the earth
approximately 6,400 kilometers DT is
also called the radio horizon of the
transmitting antenna with reference to
figure the maximum line of sight
distance D n between the two antennas
having Heights HD and HR above the earth
is given by DM equals to root 2 R HD
plus root 2 R H R where H R is a height
of receiving antenna television
broadcast microwave links and satellite
communication are some examples of
communication systems that use space
wave mode of propagation the above
figure summarizes the various modes of
wave propagation discussed so far