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Critical frequency of ionospheric layer is 10 MHz what is the maximum launching angle from the horizon for which 20 MHz wave will be reflected by the layer?
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- 0
- 30º
- 45º
- 90º
Correct Option: B
Critical frequency 'fc' is the frequency at which wave could be reflected from the ionosphere and maximum usable frequency is that frequency at which the wave could be successfully used by receiver, so we get
fmuf = fc sec i
⇒ 20 MHz = 10 MHz sec i
sec i = 2 ⇒ i = 60º
however, the angle from horizontal, we get β = 30º (i.e. 90º – 60º = 30º)
