Question

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

• A. ~ 1.2 $\times$ ${10}^{12}{m}^{-3}$
• B. ~ ${10}^6{m}^{-3}$
• C. ~ ${10}^{14}{m}^{-3}$
• D. ~ ${10}^{22}{m}^{-3}$

Answer 1

The correct option is A ~ 1.2 $\times$ ${10}^{12}{m}^{-3}$

The critical frequency of a sky wave for reflection from a layer of atomsphere is given by
$f_c$ = 9 ${\left(N_{max}\right)}^{\frac{1}{2}}$
$\Rightarrow$ 10 $\times {10}^6=9{\left(N_{max}\right)}^{\frac{1}{2}}$
$\Rightarrow$$N_{max}$ = ($\frac{10\times {10}^6}{9}{)}^6$ $\approx$ 1.2 $\times$ ${10}^{12}{m}^{-3}$