28 Radio Propagation

It’s really not Witchcraft 28 - Radio Propagation28 - Radio Propagation

Q Q - What happens to Radio - What happens to Radio Waves during the day Waves during the day

and during the night? and during the night?

AA – – It’s all about sunspots, the great It’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

Ground WaveAre signals that travel on the surface of the earth for short distances

SkywaveAre signals that reflect off the Ionosphere layers. It is the primary mode of long distance communication.

Ionospheric Layers 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 Mhz

Waves and Ionospheric Layers 2Waves and Ionospheric Layers 2

AbsorptionThe D and E layers absorb signals below 4 Mhz during the day

Critical FrequencyThe highest frequency at which reflections are return to earth from a vertical incidence

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 SkipWhen the E layer becomes highly charged permitting reflection of signals up to 200 Mhz for a few minutes to a few hours

Tropospheric DuctingWhere waves get trapped between layers and goes long distances. Usually happens over water.

Wave Angle The angle at which radio waves leave the earth and reflect off the Ionosphere and back to earth. The angle determines the skip distance

FadingFading 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 direct path

You Should Know!You Should Know!

OWF = Optimum working frequencyMUF = Maximum Working FrequencyCRITICAL Frequency = The highest frequency reflected back to earth at vertical incidence

PolarizationThe polarization of an electromagnetic wave is determined by the “E” field

SunspotsMaximum sunspots (and radio activity) occur every 11 years

IonizationThe ionization level of the ionosphere reaches it’s minimum just before sunrise

ReflectionVHF or UHF signals transmitted towards a tall building are often reflected

We Are Done !We Are Done !

73 de Lee, ZL2AL73 de Lee, ZL2AL