Question
Maximum useable frequency $(MUF)$ in $F$ -region layer is $x$ , when the critical frequency is $60 \,MHz$ and the angle of incidence is $70°$. Then $x$ is.......$MHz$
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Answer
(c) $MUF = \frac{{{f_c}}}{{\cos \theta }} = \frac{{60}}{{\cos 70^\circ }} = 175\,MHz$
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