Question

For sky wave propagation of $10\, MHz$ signal, what should be the minimum electron density in ionosphere?

• A. $\sim1.2 \times 10^{12} m^{-3}$
• B. $\sim 10^{6} m^{-3}$
• C. $\sim 10^{14} m^{-3}$
• D. $\sim 10^{22} m^{-3}$

Answer 1

Answer: (A)

$\sim1.2 \times 10^{12} m^{-3}$

Answer 2

The critical frequency of sky wave undergoing reflection from a layer of atmosphere is $f_{c}=9 \sqrt{N_{\max }}$ where $N$ is electron density per $m ^{3}$. $\therefore N_{\max } =\frac{f_{c}^{2}}{81}=\frac{\left(10 \times 10^{6}\right)^{2}}{81}$ $=1.2 \times 10^{12} m ^{3}$