TROPOSPHERIC PROPAGATION

TROPOSPHERE

• The lowest layer of Earth’s atmosphere.• Starts at Earths surface and goes up to a

height of 7-12Km above sea level.• Almost all weather occurs in this layer.• Is heated from below and the top of the

troposphere is cold.

3 MODES OF PROPAGATION

Tropospheric scattering Tropospheric bending Trophosperic ducting

TROPOSPHERIC SCATTERING

Commonly used to propagate around 800Km path lengths.

Used on frequencies above 500Mhz. Ideal for remote telemetry, or other links where low to

medium rate data needs to be carried.

HOW IT PROPAGATES

A transmitter launches a high power signal that passes through the atmosphere into outer space.

Small amount is scattered when passes through troposphere and passes back to earth.

Refractive index of the atmosphere varies according to a variety of factors. (temperature, atmospheric pressure, and water vapor pressure)

ADVANTAGES Reliable regardless of the prevailing tropospheric

conditions Can propagate in large distances Can propagate greater than the line of sight Cheaper than using satellites Used in medium speed data transmission

DISADVANTAGES

Requires high power transmitters, sensitive receivers and high gain antennas

Prone to blurring effect Not suitable for high speed data transmission

TROPOSPHERIC BENDING Under such condition radio propagation can travel

greater distances over 2000Km or more. This form of “Lift” is less pronounced on the lower

portions of the VHF spectrum, but more apparent on some higher frequencies.

These extended distance result from much greater change in refractive index over the signal of path.

This enables the signal to achieve a greater degree of bending and follows the curvature of the earth

TROPOSPHERIC DUCTING

Cause by change in refractive index Can also occur above the Earth’s surface. It occurs when a mass of air with high refractive index has

a mass of air with a lower refractive index underneath and above it as a result of the movement of air

Signals may be confined within the elevated area of air and cannot escape and return to earth

They travel for several hundred miles and creates a skip or dead zone.

THANK YOU :)