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Single hop distance is the maximum distance between transmitting antenna to first receiving antenna measured along the surface of the earth after propagation through the ionosphere.

Ionosphere is the layer of ions at a height of 50 km to 400 km formed due ionisation by ultraviolet radiations from the sun.

D layer of ionosphere is at a height of 70 km which has a thickness of 10 km. It disappears at night and reflects VLF and LF waves.

E layer of ionosphere is at a height of 100 km and has a thickness of 25 km. It disappears at night and helps MF and HF wave propagation.

F layer is at a height of 150 km and extends upto 400 km. It remains during both day and night . time. During day time, it splits into two layers F₁ and F₂ and combines to form a single F layer during night time.

F₁ layer or kennelly-Heaviside layer is at a height of 200 km with a thickness of 20 km. reflects HF waves.

F₂ layer or Appletion layer is at a height of 300 km and has a thickness of 20 km. It is usefull in HF wave propagation.

Ground waves are the waves transmitted along or reflected from the surface of the earth. These can exist when the transmitting and receiving antennas are close to the surface of the earth.

The ground wave is vertically polarised and will transmit most effectively at a frequency less than 2 MH_Z. The AM broad cast signals travel as ground waves. The strength of the ground wave is reduced due to energy absorption by the earths surface.

Space waves are the waves that travel from the transmitting to receiving antenna in the earths troposphere (first 18 km from earths surface). Space waves have two components.One of them is line of sight ray which travels directly from transmitting to receiving antenna.The other is ground reflected wave, which reaches the receiver due to reflection from the surface of the earth. Radio transmission at frequencies above 30 MHz, TV, FM, radar use space wave propagation.

Ultraviolet radiation from the sun cause the upper atmosphere to ionize i.e. to become electrically charged. Hence a thick layer of ions formed at heights of 50 km to 400km. The ionosphere supports MF and HF wave propagation.
Its three layers are:

D layer: It is at a height of 70 km and has an average thickness of 10 km. It disappears in the night time. It reflects VLF and LF waves and absorbs MF and HF waves.

E layer: It is at a height of 100 km with a thickness of 25 km. This layer disappears at night. It helps in MF and HF wave propagation.

F layer: It is at a height of 150 km and extends upto 400 km. This layer exists during both day and night time. During day time, it splits into two layers F₁ and F₂, and combines to form a single F layer during night time.

Fading is fluctuations in the strength of radio signal. Fading occurs due to absorption in the layers of the atmosphere, loss during refraction, loss due to scattering of signals. Fading can be reduced by using repeater stations which boost up the signal strength satisfactorily to reach the receiving.

(i) l.D layer

(ii) E layer.

(iii) F layer.

Fading is the fluctuation in the strength of the radio signal.

VHF (very high frequency) (30 MHz to 300MHz).

Very high-frequency VHF (30 MHz to 300 MHz).

The paths that a radio signal can take through the space are:

(i) The ground wave

(ii) The space wave

(iii) The sky wave.