-MaheshwariDasMeghana BS

Wave propagation is any of the ways in which waves travel. With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transverse waves. For electromagnetic waves, propagation may occur in a vacuum as well as in a material medium.

Propagation of radio waves from a radiating transmitting antenna to the receiving antenna may take place in one of the following routes:

1. Ground wave propagation2. Sky wave propagation3. Space wave propagation

Sky-wave propagation

It is also called Ionosphere propagation

I this mode of propagation the EM eaves reaches the receiving point after reflection from the ionized region in the upper atmosphere called ionosphere.

Ionosphere is situated between 50km & 400km above the earth. It is divided into three basic layers (D, E & F) based on ionization density. F layer is further divided into F1 and F2 sub layers.

D & E layers are weekly ionized & exist only during day light hours. They tend to observe medium waves .

The primary effect of F layers is to cause refraction of Radio waves.

Ionosphere propagation permits extremely long distance communication 3MHz-30MHz range

Above 30MHz frequency signals are not reflected.

Most long-distance shortwave radio communication—between 3 and 30 MHz—is a result of sky wave propagation.

Since the early 1920s amateur radio operators , limited to lower transmitter power than broadcast stations, have taken advantage of sky wave for long distance communication.

The signal received are subjected to fading, in which signal strength varies with time.

The receiving point, a large number of waves follow a different number of paths

Short wave, AM radio broadcast.

Long distance, point to point communication.

Extremely long distance communication using multi-hope propagation.