Radio Wave Propagation. Ionosphere Layers. Radio Waves are Bent by the Ionosphere. F1 and F2 Ionosphere Layers Combine at Night. Critical Angle. Ground Wave, Sky Wave and Skip Zone. Great Circle Route. MUF is the highest frequency that allows a radio wave to reach the desired destination.
Stay below the Maximum Usable Frequency for the best chance for a successful contact.
MUF is affected by all of these:
Path, distance and locations
Time of day and seasons
MUF: Maximum Usable Frequency
All signals below LUF are absorbed.
When LUF exceeds MUF – No HF radio frequency will support communications along an ionosphere signal path.
LUF: Lowest Usable Frequency
We are at the bottom of Cycle 23.
Higher bands like 15 meters and 10 meters are not very good.
Sunspot Number: Daily index of sunspot activity.
Higher Sunspot Numbers = Better HF Propagation
Above 100 is good
SFI= Solar Flux Index .
“A” Index = A daily measurement of the state of activity of the Earth’s magnetic field. Based on yesterday’s K Index.
“K” Index = Readings of the Earth’s geomagnetic field updated every 3 hours.
Sometimes caused by a coronal mass ejection. These particles can take 20 to 40 hours to reach Earth.Geomagnetic Disturbance
Sometimes creates a visible aurora.
Coronal holes also disrupt HF communication.Geomagnetic Disturbance