Critical frequencies are also called 3dB frequencies halfvol

Critical frequencies are also called: -3dB frequencies, half-voltage frequencies, none of the above, half-current points

Solution

Answer is opition 3 none of these.

The critical frequency is the highest magnitude of frequency above which the waves penetrates the ionosphere and below which the waves are reflected back from the ionosphere.it is denoteed by Fc.And its value is not fixed. its depends upon electron density of ionosphere.

** In signal processing the critical frequency is also called as Nyquist frequency.