Propagation
of Specific Signals
o The type of propagation used in radio
transmission depends upon the frequency of the
signal
o Each frequency is suited for a specific
layer of atmosphere and is most efficiently
transmitted
and received by technologies adapted to that layer
™ Very Low Frequency (VLF) (Figure)
o VLF waves are propagated as surface waves
through air
o Do not suffer much attenuation in TX but
are susceptible to high levels
of
atmospheric noise I.e. electricity and heat
o Used for Long-range radio navigation and
Submarine Communication
 |
™ Low Frequency (LF) (Figure)
o Also propagated as surface waves
o Used for Long-range radio and for
navigational locators
o Attenuation is greater in the day time
when absorption of waves by
natural
obstacles increases
 |
™ Middle Frequency (MF)
o Propagated in the Troposhere
o These frequencies are absorbed by
Ionosphere
o The distance they cover is limited by the
angle needed to get the signal
reflect
from the troposhere and not enter ionosphere
o Absorption increases during the day time
o Used for AM Radio
 |
™ High Frequency (HF) (Figure)
o Use ionospheric propagation
|
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