The following image is a recent high-resolution map of Maximum Usable Frequencies (MUFs) for 3,000 kilometer radio signal paths. It is also a map showing the current location of the auroral ovals, the sunrise/sunset terminator and the regions of the world where the sun is 12 degrees below the horizon (which estimates the gray-line corridor where HF propagation is usually enhanced). This is map is similar to the plethora of constructable maps that is produced by PROPLAB-PRO Version 2.0, a very powerful radio propagation software package for IBM or compatible computers, ideal for amateur or professional radio communicators. Instructions on how to use this map follow below.
Click on PROPLAB-PRO Version 2.0 for additional map samples.
RED contour lines will appear superimposed on the MUF map if x-rays reach levels capable of producing short wave fadeouts on sunlit paths. When this occurs, the red contour lines represent the highest frequency (in MHz) that may be absorbed by the enhanced solar flare x-rays. Use this information together with our new X-ray Absorption Map to determine what frequencies and paths may avoid affects of radio signal absorption during x-ray flares.
The MUF for any 3,000 kilometer path can be determined by finding the midpoint (or half-way point) of the path and examining the MUF at that midpoint on the map by finding the labelled MUF contour value. All contours are given in MHz.
For 4,000 kilometer paths, multiply the given contoured MUF values by 1.1. The MUF for the given 4,000 km path is then determined at the midpoint of the desired path.
For longer path lengths, divide the path into
equal 3,000 or 4,000 km segments and compute the MUFs corresponding to
the two midpoints that are 1,500 or 2,000 km from each end of the
path. Then select the lower of these two MUFs.
The map shows the radio auroral zones as green bands near the northern and southern poles. The area within the green bands is known as the auroral zone. Radio signals passing through these auroral zones will experience increased signal degradation in the form of fading, multipathing and absorption.
The radio auroral zones are typically displaced equatorward from the optical auroral zones (or the regions where visible auroral activity can be seen with the eye).
The great-circle signal path from the Eastern United States to Tokyo Japan is shown along with the distance of the path (in km) and the great-circle bearing from the U.S. to Tokyo (in degrees from north).
If this signal path crosses through the
green lines indicating the position and width of the radio auroral zones,
propagation will be less stable and degraded compared to if the signal
never crossed through the auroral zones. Using your mouse, PROPLAB-PRO
will let you plot the great-circle paths and azimuths between any two points
while this display is continually updated.
The yellow Sun symbol near the equator indicates the location where the Sun is directly overhead.
The regions of the world where the Sun is exactly rising or setting is known as the Grayline and is shown as the solid gray-colored line that is closest to the Sun symbol.
The second solid gray-colored line defines the regions of the world where the Sun is exactly 12 degrees below the horizon. This line defines the end of evening twilight. Everything inside of this second line is experiencing night-time conditions.
The area between the two lines (shaded a lighter shade than the night-time sector) is known as the grayline and has special significance to radio communicators. Signals which travel inside the grayline region often experience significant improvements in propagation because of the loss of ionization in the D-region as the Sun sets. However, because the higher F-regions of the ionosphere remain strongly ionized for longer periods of time, signals with higher frequencies are able to travel to greater distances with less attenuation when they are within the grayline.
The great-circle path from the eastern U.S. to Japan is also shown with the accompanying distance (in kilometers) and bearing (clockwise from north). Notice how this path may occassionally pass into the influential auroral zones if geomagnetic activity increases or during the night-times.
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