Help & Advice

the different frequencies are refracted differently by the D,E and F layers of the Ionosphere, resulting in different skip distances (think light refracted and split by a prism into a rainbow), WSPR on band hop shows this wonderfully 

also time of day affects propagation of the various bands, higher frequencies wake up later and drop of earlier than lower frequencies, also time of year affects bands and propagation as the ionosphere over the UK gets more solar radiation during the summer keeps the higher bands open for longer each day

you will learn more about the ionosphere layers etc in the intermediate and full exams

you don't need to understand exactly how it all works, just the general trends for time of day and seasonal effects

the things to look up are MUF (max usable frequency) and LUF (lowest usable frequency),

the final thing is solar flares release material from the sun (correct name is coronal mass ejection (CME)) and if these are in our direction and the impact the earths ionosphere they can lead to HF blackouts and problems with powergrids etc CME's also cause aurora as well :)

look at Radio Communications Dashboard | NOAA / NWS Space Weather Prediction Center 

73 

Peter 

M0PWX (not pete M0PSX who runs EssexHam)