Question

why day and night frequency are required for HF communication ?​

Answer 1

It is due to the ionosphere, during the day the ionization rate of neutral atoms is high due to the sun, however at night this ionization rate is low. Therefore, during the day the ionosphere moves downward toward the earth and at night moves upward

please rank me brainlist answer I need this please

Answer 2

Answer:

Because HF radio waves depend upon the ionosphere for reflection, their propagation is affected by changes in the ionosphere. ... A good rule of thumb for the time of day is that the higher frequencies are best during daylight (10 to 29.9999 MHz) and lower frequencies work best at night (2 to 10 Mhz).

Explanation:

hope it will help you