Amateur Radio Frequency Propagation Presented by Jerry Ver

Amateur Radio Frequency Propagation Presented by Jerry Ver. Duft, ADØA

Let’s review the basics The sun influences all radio communication beyond ground-wave or line of sight ranges v Conditions vary with the time of day, season, and latitude/ longitude v REFLECTION occurs at any boundary between materials with different dielectric constants v 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 v

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

Refraction If waves were not bent:

The Ionosphere Affects frequencies below 30 mhz v 30 -260 miles above the earth’s surface v Contains free ions and electrons v Ionization depends on ultraviolet radiation from the sun v Skip distances depend upon frequency used, time of day, and density of the ionosphere v Several layers of varying distances at various heights v

Ionospheric Layers HF Communications: D, E, F 1, F 2 layers v D layer (45 -55 miles): Acts as an RF sponge with maximum absorption during daylight hours thus dictates the LUF v E layer (65 -75 miles): Effective refraction only during daylight hours v F layer (90 -250 miles: During daylight, there are two layers, F 1 and F 2 v F 1 is not an important propagation medium; the F 2 region is the primary medium supporting HF communications (200 miles); F 1 and F 2 combine onto one layer at night v

Types of Propagation Ionospheric waves (sky waves): Main portion of the radiation that leaves the antenna at angles above the horizon v Tropospheric waves: Radiation kept close to the earth’s surface due to bending in the lower atmosphere (higher HF or lower VHF) v 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 v

The Blessings of Sky Wave The medium for most all amateur radio communication below 30 mhz v The ionosphere refracts the radio wave and returns it to earth v The maximum usable frequency (MUF) is a function of how highly ionized the F region is v 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 v

The Main Inhibitor: Solar Cycles v Sunspot cycles average 10. 7 years in length v At solar maxima, the ionosphere is capable of refracting radio signals up to 40 mhz or higher v At solar minimum, refraction is reduced and frequencies above 20 mhz become unreliable v We are currently in the downward slope of cycle 23

100 Year Solar Cycles

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

Solar Indices v 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 F 2 layer thus is a good indication of conditions for HF com - SFU values run from about 50 to as high as 300 - Low values indicate low MUF; high values indicate good ionization to support long distance communications at higher than normal frequencies

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

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

Transequatorial Spread-F v Long distance VHF communication for stations equidistant from the geomagnetic equator v Hypothesized to be a result of an intensified F 2 layer during high sunspot activity v Signals have a rough aurora-like note

Geomagnetic Activity Natural variations in the geomagnetic field are classified into quiet, unsettled, active, and geomagnetic storm levels v 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 v A index (0 -400) is a daily average of the K index values v Generally, an A index at or below 15 and a K index at or below 3 is best for propagation v

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

Propagation Information Websites ARRL propagation page: http: //www. arrl. org/tis/info/propagation. html v NOAA propagation report: http: //www. sec. noaa. gov v QRZ Solar Report: www. qrz. com v Eham Propagation: www. eham. net v DX Summit: oh 2 aq. kolumbus. com/dxs/ v Solar Terrestrial Activity Report: http: //www. dxlc. com/solar v