Radio Wave Propogation Flashcards
what can variation in density between the layers within the ionosphere do to radio waves?
can bend and alter the paths of certain radio waves to such an extent they return to the earth’s surface as sky waves.
what does the ionosphere do to sky waves?
turn skywaves back into the lower atmosphere.
Radio waves in HF band are particularly susceptible to what process?
ionospheric refraction.
the amount of refraction on a particular radio signal is dependent on what?
frequency of the radio waves and the state of the ionosphere itself.
the strength of the signals for any given HF frequency can vary to what?
from hour to hour and even minute to minute
sky waves in the HF frequency band to a larger extent are the cause of what?
great range of signal reception, hence its suitability for long-distance comms.
In the HF band where are increasing ranges obtained?
from multiple-hop returns of the skywave. Aerial systems may still need to be large especially in the lower segment of HF.
what are the disadvantages of the HF band?
- susceptibility of signals to bending, reflection, atmospheric and manmade interference.
- constant presence of static
- fading is caused in port by out-of-phase reception of the skywave and the surface wave.
VHF and UHF are generally clear of what? but rely on what?
generally clear of interference but rely largely on the line-of-sight + 10% principle. meaning that signals can be received slightly below the line-of-sight path. Aerials can be small which is ideal for aircraft use.
Line-of-sight improves with what?
height of both transmitter and receiver.
what is the typical saying of line-of-sight improvement?
follows that the higher the transmitter above sea level and or the higher altitude of the aircraft. the greater the range of VHF signals.
