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Amateur Radio Frequency Propagation Presented by Jerry VerDuft, ADØA.

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Presentation on theme: "Amateur Radio Frequency Propagation Presented by Jerry VerDuft, ADØA."— Presentation transcript:

1 Amateur Radio Frequency Propagation Presented by Jerry VerDuft, ADØA

2 Let’s review the basics  The sun influences all radio communication beyond ground-wave or line of sight ranges  Conditions vary with the time of day, season, and latitude/ longitude  REFLECTION occurs at any boundary between materials with different dielectric constants  Radio waves may be reflected by buildings, trees, vehicles, the ground, water, ionized layers in the outer atmosphere, or different air masses having different temperatures and moisture content

3 The Basics Continued  Some radio energy will be absorbed by the medium it passes through, some passes on through the material  REFRACTION is the bending of a wave as it passes through one medium into another  Bending occurs because the wave is at a different speed in the new material  Amount of bending increases at higher frequencies  Speed of waves through the atmosphere change as the temperature, air density and levels of ionization are different  Most HF bands depend upon refraction

4 Refraction If waves were not bent:

5 The Ionosphere  Affects frequencies below 30 mhz  miles above the earth’s surface  Contains free ions and electrons  Ionization depends on ultraviolet radiation from the sun  Skip distances depend upon frequency used, time of day, and density of the ionosphere  Several layers of varying distances at various heights

6 Ionospheric Layers  HF Communications: D, E, F1, F2 layers  D layer (45-55 miles): Acts as an RF sponge with maximum absorption during daylight hours thus dictates the LUF  E layer (65-75 miles): Effective refraction only during daylight hours  F layer ( miles: During daylight, there are two layers, F1 and F2  F1 is not an important propagation medium; the F2 region is the primary medium supporting HF communications (200 miles); F1 and F2 combine onto one layer at night

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8 Types of Propagation  Ionospheric waves (sky waves): Main portion of the radiation that leaves the antenna at angles above the horizon  Tropospheric waves: Radiation kept close to the earth’s surface due to bending in the lower atmosphere (higher HF or lower VHF)  Ground waves (surface waves): Radiation directly affected by the earth’s surface - Earth-guided surface wave - Vertically polarized and absorbtion increases with freq - Travels much further over water than over land

9 The Blessings of Sky Wave  The medium for most all amateur radio communication below 30 mhz  The ionosphere refracts the radio wave and returns it to earth  The maximum usable frequency (MUF) is a function of how highly ionized the F region is  The lowest usable frequency (LUF) is a function of obsorbtion, signal-to-noise ratio, power and transmission mode; Correlates with movement of the sun and peaks at noon

10 The Main Inhibitor: Solar Cycles  Sunspot cycles average 10.7 years in length  At solar maxima, the ionosphere is capable of refracting radio signals up to 40 mhz or higher  At solar minimum, refraction is reduced and frequencies above 20 mhz become unreliable  We are currently in the downward slope of cycle 23

11 100 Year Solar Cycles

12 Solar Radiation  Electromagnetic: X-rays, Ultraviolet (UV), Extremely Ultraviolet (EUV)  During solar flares, UV and X-ray emissions increase causing increased signal loss on HF  X-ray flares: C (smallest), M (medium size), X (the largest) – in 1-8 Angstrom range

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14 Solar Indices  SOLAR FLUX is the basic indicator of solar radiation - Solar Flux Units (SFU) is the amount of solar noise or flux that is emitted at 2800 mhz (10.7 cm) - SFU equates to the level of ionization in the F2 layer thus is a good indication of conditions for HF com - SFU values run from about 50 to as high as Low values indicate low MUF; high values indicate good ionization to support long distance communications at higher than normal frequencies

15 Sunspot Numbers  SMOOTHED SUNSPOT NUMBERS (SSN) reflect the level of sunspot activity  Calculated using 6 month of data before and 6 months of data after the desired month + the desired month  Vary from 0 to 200 with an average of 100 at max  High SSNs are best for HF propagation  Low SSNs are best for LF propagation

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17 Coronal Mass Ejections  High particle emissions (protons and alpha particles) cause higher absorption in polar regions  Low particle emissions cause magnetic field disturbances, auroras, and sporadic E  Sporadic E propagates 50 and 144 mhz signals

18 Transequatorial Spread-F  Long distance VHF communication for stations equidistant from the geomagnetic equator  Hypothesized to be a result of an intensified F2 layer during high sunspot activity  Signals have a rough aurora-like note

19 Geomagnetic Activity  Natural variations in the geomagnetic field are classified into quiet, unsettled, active, and geomagnetic storm levels  K index (0-9) is a quasi-logarithmic local index of 3- hourly range in magnetic activity relative to an assumed quiet-day curve for a single geomagnetic observatory site  A index (0-400) is a daily average of the K index values  Generally, an A index at or below 15 and a K index at or below 3 is best for propagation

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21 HF Band Prediction Characteristics  80 & 40 mtrs – good bands for distant communication especially during sunspot minimum  30 mtrs – allows greater distances than 40 mtrs at night  20 mtrs – most popular long haul band during all phases of the sunspot cycle but closes down at night during winter and sunspot minimum  15 mtrs – during sunspot minimum few stations heard day or night  10 mtrs – with low absorption allows good communication with relatively low power during daytime

22 Propagation Information Websites  ARRL propagation page:  NOAA propagation report:  QRZ Solar Report:  Eham Propagation:  DX Summit: oh2aq.kolumbus.com/dxs/oh2aq.kolumbus.com/dxs/  Solar Terrestrial Activity Report:


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