It’s really not Witchcraft
28 - Radio Propagation28 - Radio Propagation
QQ - What happens to Radio- What happens to Radio
Waves during the dayWaves during the day
and during the night?and during the night?
AA –– It’s all about sunspots, the greatIt’s all about sunspots, the great
Ionospheric sponge and ReflectionsIonospheric sponge and Reflections
You Need to Know about Angle of RadiationYou Need to Know about Angle of Radiation
Angle of radiation is not just a theory…Angle of radiation is not just a theory…
It’s real – if you want to work DXIt’s real – if you want to work DX
High angle of radiation – Little or no reflection and no DXHigh angle of radiation – Little or no reflection and no DX
Low angle of radiation – good reflection and you work the DX!Low angle of radiation – good reflection and you work the DX!
Skip Zone TerminologySkip Zone Terminology
The Skip Zone is the far end of the ground wave to
where the refracted wave first returns to earth
The Skip Distance is from the transmitter to where
the refracted sky wave first returns to earth
Waves and Ionospheric LayersWaves and Ionospheric Layers
Are signals that travel on the surface of the earth for short distances
Are signals that reflect off the Ionosphere layers. It is the primary mode of
long distance communication.
The F1 and F2 Layers - are the highest and separate during the day and
combine during the night
The E Layer - lower and more dense. Densest at noon and disappears
when the sun goes down
The D Layer – Only exists during the day and absorbs all signals below 4
Waves and Ionospheric Layers 2Waves and Ionospheric Layers 2
The D and E layers absorb signals below 4 Mhz during the day
The highest frequency at which reflections are return to earth from a vertical
MUF (Maximum Useable Frequency)
• If the frequency used is too high, it will pass through the layers and
disappear into space.
• The MUF varies with solar activity and time of day.
• The MUF is the highest frequency that will reflect off the Ionosphere.
Other Propagation TermsOther Propagation Terms
Sporadic E Skip
When the E layer becomes highly charged permitting reflection of signals up
to 200 Mhz for a few minutes to a few hours
Where waves get trapped between layers and goes long distances. Usually
happens over water.
The angle at which radio waves leave the earth and reflect off the Ionosphere
and back to earth. The angle determines the skip distance
Fading happens when signals return to earth by two or more separate paths
and cancel each other out. Aircraft, Mountains andionospheric layers may
also reflect part of a signal while the other part of the signal takes a more
You Should Know!You Should Know!
OWF = Optimum working frequency
MUF = Maximum Working Frequency
CRITICAL Frequency = The highest frequency reflected
back to earth at vertical incidence
The polarization of an electromagnetic wave is determined by the “E” field
Maximum sunspots (and radio activity) occur every 11 years
The ionization level of the ionosphere reaches it’s minimum just before
VHF or UHF signals transmitted towards a tall building are often reflected
We Are Done !We Are Done !
73 de Lee, ZL2AL73 de Lee, ZL2AL