4. Propogation Of Radio Waves Flashcards
Which layer in the ionosphere reflects HF radio waves?
In the ionosphere, the F layer reflects HF radio waves.
What phenomena can cause deterioration of HF communication quality?
HF communication quality can be deteriorated by
- magnetos storm,
- Dellinger phenomena, and
- fading depending on the strength of the Sun’s activity.
Also by echo
What happens to the energy of ground service waves
The energy of ground service waves is adsorbed by the earth’s surface.
Which frequencies attenuate more?
VHF and higher frequencies attenuate more than lower frequencies.
Which frequencies are limited to line of sight?
Propagation range of VHF and higher frequencies is limited to line of sight.
How are VHF signals affected by weather phenomena?
In the troposphere, weather phenomena affect radio signals of VHF and higher frequencies causing fading and scattering.
What affect do temperature inversions have on radio wave propagation?
A temperature inversion may form a radio duct that may cause duct fading
Are MF radio waves restricted to LOS?
No
MF radio waves follow the curvature of the earth.
MF radio waves are used for broadcasting stations and NDB stations.
What effect reduces NDB night coverage?
MF night effects reduce NDB’s reliable coverage due to disappearance of D layer at night and the subsequent reflection of MF radio waves at the E layer. These reflections may cause interference.
What determines the frequencies used for HF communications?
Frequencies applicable to HG communications are between the lowest frequency that penetrates the D and E layers (LUF) and the highest frequency that reflect off the F layer (MUF).
What happens to HF radio signals close to the MUF?
HF radio signals with frequencies close to the MUF alternate penetration and reflection at the F layer
Dillenger Phenomenon
An increase in the ionisation of the D layer due to intense solar flare causes attenuation of HF signals in the D layer leading to possible communications blackout
