Amateur Radio Current Conditions

First of all, many variables are involved in predicting DX landing zones and very few them are exact.  The calculator below along with the maps above can give you a pretty good idea of where, when and how well you will be able to communicate using skywave communications.   

a) Knowing the radiation takeoff angle (angle of elevation) of the antenna in use is very helpful for accurate projections.

b) The height of the ionosphere (you can estimate 200 mile altitude as none of this is exact).

c) I know my 10m 4 element yagi has a TO angle of about 20 degrees.

Given the above, I know that my first bounce off the ionosphere F layer will be about 600 miles from my home.  On its way back down from the ionosphere it should meet up with the earth at about 1,200 miles from my transmission point.  If I'm on 10m using the yagi following the Great Circle path, all refractions off ionosphere must have a minimum maximum usable frequency of 29 mhz.  With each hop, the hops tend to elongate but I know that from Atlanta to Europe I will need to hop 3 or 4 times depending on destination.  Also keep in mind you will have dead spots on the ground between the hops.

The foF2 map above is referred to as the critical frequency. Critical frequency is the highest frequency at which a signal broadcast straight up in the air (90 degrees to the earth's surface) will bounce back to earth.  For DXing a signal is more parallel to the earth and will typically refract off the ionosphere somewhere around 3.5 to 4 times the critical frequency.  3.5 to 4 times the critical frequency is what's referred to as the maximum usable frequency as it relates to skywave propagation.

I like using the Australia Space Weather map (shown above) as it depicts the ionosphere more like a storm weather radar and intensity along with movement.  This type of graphical depiction allows me fairly accurately predict, for instance, when Europe will come in for skywave on 10 meters each morning.

The D Layer absorption map estimates the impact the D Layer will have on various frequencies during the day.  The scale of the right shows the amount of attenuation on each band/frequency.  The map itself depicts which frequencies are affected by at least one db of absorption.     

Select elements = height and base

Height h = 200 (varies in miles ea. day) for ionosphere

Base angle 0 = 20 (varies based on degrees of antenna radiation angle)

Output = element of "base a" is length of skip (in miles)

see link in hyperlink section below for an isosceles triangle calculator