(c) Time of year - During the summer months the ionosphere layers receive more radiation from the sun. From this it follows that the upper HF bands will stay open for longer hours. Also, it is not unusual to find that some bands remain open all night during the summer (particularly 20 meters). See also (e) below.

(d) Geographic location - What parts of the world you can work at any one time is heavily influenced by (a), (b) and (c) above. Let's take a few examples to illustrate this. Suppose you want to work from the UK to USA on 80 meters. We see that 80 meters is basically a night time band, so you will need to pick a time when both countries are in darkness. You can see that winter is therefore the best time of year for this as the hours of darkness are longer. Also the noise levels are considerably lower on 80 meters during the winter (during sunspot maxima noise will also be higher on this band).

The next example is UK to New Zealand on 10 meters. This is a considerable distance and the signals would need several reflections from the ionosphere to do the job. This would normally only happen near or at the sunspot maxima on this band. Next, both countries would have to be in daylight, so we are looking at times of around 0700 UTC and 12-1400 UTC assuming winter in the northern hemisphere and summer in the south.

(e) Beam headings - If you look at a world map from an atlas the earth appears flat. Say if you wanted to point your beam from the UK to Japan, such a map would show the heading as roughly south east. Such a map does not take into account the curvature of the earth and the true heading would be more north-north-east.

For accurate beam headings use a Great Circle world map which does take into account the spherical nature of the earth.

It can be seen that although this heading covers greater distance, it is mostly over open sea which can be more effective for multiple reflections from the ionosphere possibly resulting in stronger signal strengths than the short path. Short and long paths will normally occur at different times of the day, for instance UK to new Zealand on 40m in the morning will be short path, with the long path open in the evening. Such paths are also effected by time of year. For instance it may be possible to work Fiji from the UK on the higher bands in the winter by beaming south over Antarctica, which will be in the full daylight of summer. The North pole however will be in darkness due to winter and there will probably be no propagation in that direction.

A guide to the state of propagation can be gauged from the SFI (solar flux index) which can be found on DXclusters on packet radio and the internet, and also in ham radio news bulletins etc. As a rough guide the higher the SFI the better the propagation. At the bottom of the sunspot cycle SFI's will be around the 100 mark. Recently as we approach the peak of the latest cycle, SFI's over 200 have been recorded. So in summary, during sunspot maxima concentrate on the higher bands (particularly 10 meters), and during minima seek DX on the lower bands.