now we will study about the electromagnetic
wave propagation in space , here we can see
- this diagram shows a typical communication
system, in which the signal fed to the transmitter
is converted in to , a form , in which it
can be transmitted to space- that is high
frequency form as we have discussed.
that electromagnetic wave transmission in
space, must be only in high frequency because
at low frequencies there are 2 problems- one
is size of antenna other is the low radiation
power , so here when the transmitting antenna-
this is the transmitting antenna .
which , transmits electromagnetic waves in
space and – this is the receiving antenna
which receives the electromagnetic waves , and
finally receiver , receives- and supply the
signal to further amplifying and transducing
stages , now in this situation when we talk
about this space through which the electromagnetic
waves are broadcasted- or, transmitted or
propagated – from transmitting antenna to
the receiving antenna .
there are , 3 general ways.
in which.
electromagnetic wave propagation . 
take place, in space , we will study about
all these 3 waves one by one in detail . the
very first is , ground waves , which are-
generally at frequencies less than , 2 mega
hertz , the second is- sky waves , which are
frequencies in the range 3 mega hertz to approximately
30 mega hertz .
you must be, vigilant that there is no clear
demarcation of frequencies at which the ground
and sky waves can be used , even at 2 to 3
mega hertz , ground waves and sky waves both
can be used, so there is no clear demarcation.
the third one is space waves , which are at
generally more than . 40 mega hertz frequencies
which are used- about all these 3 kinds of
waves we will discuss one by one in detail
in coming sections , but these are the .
broad view about - the electromagnetic wave
propagation in space , whenever, from transmitting
antenna to the receiving antenna electromagnetic
waves are carrying - which are carrying the
signal are broadcasted , these are propagated
in either of these 3 forms , which we will
discuss 1 by 1 now .
