1. The Sun and HF Propagation
Lu Romero – W4LT
1/2018

2. Here is what we are going to discuss:
Basic HF Propagation principles
How solar activity influences band conditions
Sunspots, Flares and CME’s (Oh My!)
Which band should I use to reach an area?

3. And a Quick Disclaimer:
People spend lifetimes studying this stuff! I have less than an hour to explain the basics to you. This presentation will be a 50 thousand foot view of the subject.

4. Basics of Wave Propagation:
There are two basic ways
Groundwave
Skywave

5. Propagation Basics:
The Sun influences all communication modes beyond Ground Wave or line of sight.
HF Conditions will vary with time of day, season and location on the face of the earth.
All wave reflection happens at any boundary between two materials with different properties.
Radio waves can be reflected by any and all physical objects they encounter.
Some energy is ALWAYS lost as a radio wave propagates through any medium.

6. Propagation Basics:

7. Propagation Basics:

8. Propagation Basics:
REFRACTION (Not Reflection) is what causes a wave to “bend” in the ionosphere.
REFLECTION is what causes a wave to “bounce off” objects in the “Physical World”
Waves bend because they enter and exit the “medium” at different speeds.
The higher the frequency, the more the wave bends.
Reflection causes “multipath” additive and subtractive effects (fading) mostly on ground and line of sight waves

9. Propagation Basics:
Depending on the frequency and power…

10. Propagation Basics:

11. Propagation Basics:
Traversing every boundary takes its toll…

12. Solar Radiation and Propagation:
Affects the physical properties of the ionospheric layers
Influences refraction of frequencies below 30-50MHz
Ionization (amount of free electrons and ions) depends on Ultraviolet and X-Ray radiation from the sun
“Skip” distances are influenced by fequency, ionization levels (ion density) and ionospheric layer height, along with angle of radiation of the skywave
Higher ionization refracts more dense wave fronts… Wave front density influences received signal strength

13. Solar Radiation and Propagation:
Solar Radiation is not constant, and varies:

14. Solar Indices that “count”:
Solar Flux (SFU)
Smoothed Sunspot Number (SSN)
X-Ray Flux
Geomagnetic Activity

15. Solar Indices – Solar Flux (SFU)
Amount of “Solar Noise” at 2.8GHz (10.7 cm band)
The level of ionization in the F2 layer = Good approximation of HF wave refraction coefficient.
SFU will run from a low of around 50 to a high of around 300 units.
Low numbers reflect low Maximum Useable Frequencies; High numbers indicate good ionization
Higher the SFU – Better HF conditions

16. Solar Indices – Sunspot Number (SSN):
SSN reflects the level of sunspot activity
Is calculated using a 6 month sliding record(6 months before and adjusted data for the current activity)
Varies from 0 to 200 with an average of around 100 at its maximum
High SSN means great HF propagation and not so good LF propagation
Low SSN means not so good HF propagation and great LF propagation
High band ops like High SSN – Low band ops are the opposite

17. Solar Radiation and Propagation:
Current Solar Cycle:

18. Solar Indices – X-ray Flux
Impacts the amount of absorption in the ionosphere
Defines how Solar Flares impact HF propagation on the SUNLIT side of the planet
Is a measure of the strengths of solar flares.
Takes 8 minutes to affect the earth (relativistic speeds)
Indexed via letter indications
High Flux = Radio Blackouts due to absoption usually in the D-Layer

19. Solar Indices – X-ray Flux
Solar X-ray flux (flare strength)
Level
Flux (watts/sq meter)
Description A
less than 10-8
Very Low Background
between 10-8 and 10-7
Low Background B
between 10-7 and 10-6
Moderate Background C
between 10-6 and 10-5
High Background/Low Flare M
between 10-5 and 10-4
Moderate Flare X
between 10-4 and 10-3
High Flare Y
greater than 10-3
Extreme Flare

20. Solar Indices – X-ray Flux
Solar X-ray flux (flare strength)

21. Solar Indices – Geomagnetic Storms
Different from Radio Flux
Associated with Coronal Mass Ejections
Variable speed – Particulates – Not relativistic
Influences Magnetic Field of earth
Associated with Aurora events

22. Solar Indices – Geomagnetic Storms
Coronal Mass Ejections
Lots of “atomic particles” like free protons and alpha particles (ions, stripped atoms) cause absorption to be increased especially in the polar regions (Auroral Absorption)
Magnetic Field disturbances enhance Sporadic E propagation especially from 28 to 144MHz (especially 50MHz)
Impart a “rough” or “watery” sound to HF signals, especially those that have to traverse the “Auroral Oval” at higher angles.

23. Solar Indices – Geomagnetic Storms

24. Solar Indices – Geomagnetic Storms

25. Solar Indices – Geomagnetic Storms
Variations in the earth’s magnetic field are classified as QUIET, UNSETTLED, ACTIVE and STORM
The K index: A number over a 3 hour range of magnetic activity. Range is 0 to 9 – Lower is better conditions
The A index: A number standing for the daily average of K index values Range is 0 to 100 – Lower is better
Remember, what is good for high band HF (20m – and up) is inversely proportional for low band HF (30m and below). Usually, bad high band = good low band condx

26. Conclusions and Theories
Propagation predictions are both Art and Science
They are PREDICTIONS. Conditions change dynamically
When the band is capable of propagation and no one is using it, is it really dead?
New digital modes are revealing that “dead” bands are not really dead!
The amount of variables in this subject is immense! Practice makes perfect – Get on the radio and see what you can work!

27. Conclusions and Theories
160 (and below) Generally night time winter bands – best under low SSN conditions for DX
Generally: 80 and 40 meters are good bands for communication – Short distance during the day – Long distance at night. Less QRN in winter (fewer Thunderstorms)
30 meters – allow greater distance communication at night than 40 meters

28. Conclusions and Theories
20 meters – Bread and Butter band – usually open intracontinentally during the day and intercontinentally in the morning and evening – closes early in low sunspot times, stays open all night in higher sunspot times
15 meters – Daytime band only during low sunspot times – Great DX potential during high sunspot times
10 meters – Great DX propagation with low power during high sunspot times – usually daytime only during low sunspots
6 meters – considered a VHF band, but acts like 10 in high SSN periods

29. More information on Propagation
QRZ Solar Report –
NOAA Space Resources –
Solar Activity Report –
Australian AF -
HFLink -
Absorption -
ARRL –

30. The Sun and HF Propagation
Questions and Comments
Lu Romero – W4LT –