question_answer

A ground receiver is receiving a signal at

(i) 5 MHz and

(ii) 100 MHz

transmitted from a ground transmitter at a height of 300 m located at a distance 100 km. Identify whether it is coming via space wave or sky wave propagation or satellite transponder. Radius of the earth \[\simeq 6.4\times {{10}^{6}}m,\] \[{{N}_{\max }}\] of the ionosphere \[={{10}^{12}}\,\,{{m}^{-3}}.\]

Answer:

Maximum distance covered by space wave communication \[=\sqrt{2{{R}_{e}}h}\] \[=\sqrt{2\times 6.4\times {{10}^{6}}\times 300}=62\,km\] Since, receiver transmitter distance is 100 km, this is ruled out both for (i) and (ii) further \[{{f}_{c}}\] for ionospheric propagation is, \[{{f}_{c}}=9{{({{N}_{\max }})}^{1/2}}=9\times {{({{10}^{12}})}^{1/2}}=9MHz\] So, the signal of 5 MHz \[(<{{f}_{c}})\] comes via ionospheric mode while signal of 100 MHz comes via satellite mode.