Mumbai University > Electronics Engineering > Sem 5 > Electromagnetic Engineering

Marks: 5 Marks

Year: Dec 2014

a) Critical frequency:

It is that highest frequency radio wave, which sent normally towards layer of ionosphere gets reflected back & returns to the earth.

$f α \sqrt{N} \\ f= g \sqrt{N} \\ f= g(N_{\max} )^{\frac{1}{2}}$

where, N → free electron density

b) Maximum usable frequency (MUF):

It is that highest frequency of radio waves which when sent at some angle towards ionosphere, gets reflected and returns to the surface of the earth.

$MUF=\dfrac{f_c}{\cos ⁡i} \\ MUF=f_c.\sec⁡(i) \\ Also, MUF=f_c \sqrt{1-\dfrac{D^2}{4h^2}}$

Where , $\text{D → skip distance} \\ \text{i → Angle between normal and direction of incident wave.}$

c) Optimum working frequency (OWF):

The frequency normally used for ionosphere transmission is known as optimum working frequency. Usually, it is taken as 15% of MVF.