Question

Suppose a ray is incident normally in the ionosphere region with electron density 25×10^10/cm^3,  then the Maximum usable frequency is _____

(a) 5GHz

(b) 45MHz

(c) 4.5MHz

(d) 125GHz

I had been asked this question by my college professor while I was bunking the class.

My doubt is from Maximum Usable Frequency in section Virtual Height, Critical Frequency and Muf of Antennas

Answer 1

Right choice is (c) 4.5MHz

To elaborate: \(f_c=9\sqrt{N \,max}\) where Nmax= electron density and angle of incidence is ἰ = 0 (given)

                    ∴ \(f_c = 9\sqrt{25×10^{10}} = 4.5MHz\)

⇨ And fMUF = fc secθi = fc = 4.5MHz