Long range radio transmission is possible when the radiowaves are reflected from the ionosphere. For this to happen the
frequency of the radiowaves must be in the range :
80 - 150 MHz
8 - 25 MHz
1 - 3 MHz
150 - 500 kHz
As we have learnt,
Value of critical frequency -
- wherein
Nmax is maximum electron density of the ionosphere in per m3 .
For reflection to happen from ionosphere frequency should be less than critical frequency
Frequency should be less than than 30 MHz
Option 1)
80 - 150 MHz
Option 2)
8 - 25 MHz
Option 3)
1 - 3 MHz
Option 4)
150 - 500 kHz
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