A ground receiver station is receiving a signal at (a) 6.0 MHz and (b) 110 MHz, transmitted from ground transmitter at a hight of 300 m located at a distance of 100 km. Identify whether it is coming via space wave or sky wave propagation or satellite transponder. Radius of earth `= 6.4 xx 10^6m`, maximum number density of electrons in ionosphere = ` 10^(12)m^(-3)`.

Explanation

Here, `h = 300 m, R = 6.4 xx 10^6m,`
`N_(max) = 10^(12) m^(-3)`
For space wave propagation, Maximum
distance covered by space wave communication
`d = sqrt (2Rh) = sqrt(2 xx 6.4 xx 10^6 xx 300)`
`= 61.96 xx 10^3 m ~~ 62 km`
Since the distance between transmitter and
receiver is 100 km, hence for the given frequency
signals of 6.0 MHz and 110 MHz, the propagation
is not possible via space wave propagation.
For sky wave propagation, the critical frequency,
`v_c = 9 (N_(max))^(1//2) = 9 xx (10^12)^(1//2) = 9 xx 10^6 Hz`
`= 9MHz`
Since the frequency of signal (a) i.e. 6.0 MHz
is less than `v_c`, so its propagation via sky wave is
possible. Since the frequency of signal (b) i.e., 110
MHz is greater than `v_c`, hence its propagation is
not possible via sky waves. For that, satellite
communication is used.