Q.Explain the ionospheric propagation with specially mentioning the features of the different layers.

Ionospheric propagation relies on distinct ionized layers, each of which affects radio waves differently. …

[!TLDR]

Ionospheric propagation reflects HF sky waves off the D, E and F layers; the F (especially F2) layer is the most useful, present day and night.

Ionospheric propagation: Signals radiated into the upper atmosphere are refracted and reflected back to earth by the ionized layers of the ionosphere (about 50–400 km high), enabling long-distance HF communication. Whether a wave returns depends on the layer's charge density and on the wave's frequency and angle of incidence.

Features of the different layers:

1. D layer — average thickness about 10 km, at an altitude of about 70 km; weakly ionized; disappears at night; reflects VLF and LF waves and absorbs MF and HF waves.
2. E layer (Kennelly–Heaviside layer) — average thickness about 25 km, at an altitude of about 100 km; disappears at night; helps MF and partially HF wave propagation.
3. F layer (Appleton–Barnett layer) — begins around 150 km and extends up to 400 km; present both day and night; highly ionized and most effective on HF signals. During the day it splits into:
   • F1 layer — average altitude about 200 km; partially reflects HF waves.
   • F2 layer — average altitude about 300–400 km; the most useful layer for HF propagation; changes its altitude seasonally with the earth's revolution. …