What is meant by critical frequency for sky wave propagation? Write an expression for the critical frequency in terms of the maximum electron density of the ionosphere. What is the range of variation of frequency for this critical frequency?      

Dear Student,

Please find below the solution to the asked query:
 

Critical frequency: 

In sky wave communication the critical frequency is the maximum frequency bellow which the signal can be transmitted from one point to another point via reflection from ionosphere. Above this frequency the signal will be transmitted through ionosphere. 

Relation with maximum electron density: 

$f_{critical}=9\sqrt{N}$, where N is the maximum electron density. 

Range of critical frequency: 

The range of critical density varies from 3 to 30 MHz. 

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