A ground reciver is receiving a signal at (a) 5 MHz, and (b) 100 MHz, transmitted from a ground transmitter at a height 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^(6) m , N_(max)` of ionosphere `= 10^(12) m^(3)`]

Explanation

Maximum distance covered by space wave communication `= sqrt(2rh)=sqrt(2xx6.4xx10^(6)xx300)=62k`
Since receiver-transmitter distance is 100 km, this is ruled out both for 'a' and 'b'
Further,`f_(c)` for ionospheric propagation is `f_(c) = 9 (N_(max))^(1//2) = 9 xx (10^(12))^(1//2) = 9 MHz`
so the 'a' signal of 5 MHz `(lt f_(c))` comes via ionospheric mode while the 'b' signal of 100 MHz comes via the satellite mode.