The KC2G MOF/LOF Map

Sep 11, 2023

The KC2G ionospheric data website is best known in the amateur radio world for its MUF (Maximum Usable Frequency¹) contour map, which is used by many radio amateurs to determine which bands to use for long-distance (DX) contacts. But the MUF doesn't tell the whole story: it's only valid for long-distance communications, and in any event interpreting the MUF map for amateur radio use is more of a vibes-based art than an exact science. But it doesn't have to be that way: an undocumented feature of the KC2G propagation site allows one to generate on demand a contour map that gives the highest usable frequency for communications between a specified point and every point on the map. The website calls these maps Maximum Operating Frequency (MOF) and Lowest Operating Frequency (LOF) maps. This makes determining the feasibility of and frequency for a desired contact as simple as reading a contour map. As with the MUF map, the data used to generate each MOF/LOF map are updated every five minutes, allowing for amateur radio operators to get both up-to-date and location-specific propagation maps. A map can be accessed at https://prop.kc2g.com/api/moflof.svg?grid=cn84ql&metric=mof_sp; replace cn84ql with your grid locator and mof_sp with lof_sp to get the LOF map instead of the MOF map.

An example MOF map for Portland, OR is given below. The transmitter location is marked by a star; surrounding the star is the area roughly in line of sight to the transmitter location; communications within this area can use any frequency. Surrounding that area are concentric circles of steadily-increasing frequency; this reflects the fact that, if a signal at steeper angles of incidence to the ionosphere is to be reflected, that signal must have a lower frequency than one with a shallower angle of incidence (all else being equal). The LOF map is similar in nature.

A MOF contour map for communications between the grid
square CN84ql and any point on the globe; the map itself contains an
equirectangular projection of the world, upon which is overlaid a
contour map with a range of frequencies mapped to a color spectrum.
The map has a color key on the bottom.

Below, you can easily retrieve the MOF/LOF map for your grid square. If you don't know your grid square, there are several tools available online (such as this one from QRZ and this one from AMSAT) to help you calculate it from your coordinates; to find your coordinates, use a good mapping app on your cellphone or look up your address on OpenStreetMap

The Maximum Usable Frequency (MUF) is the highest frequency that supports ionospheric propagation between two points. The MUF and its counterpart LUF (Lowest Usable Frequency) vary throughout the day and year because the ability of the ionosphere to reflect radio waves at a certain frequency depends on its exposure to solar radiation. MUF is typically quoted as the maximum frequency supported by the ionosphere at that particular point for a radio wave traveling a distance of 3000 km; the distance traveled is significant because the ability of the ionosphere to reflect radio waves depends on the angle of incidence of the wave, which in turn depends on the distance between the origin of the radio wave and the point at which the wave is reflected, which in turn depends on path length.

This is in contrast to the critical frequency (\(f_{0F2}\)), which measures the highest frequency of a vertically-incident wave that will be reflected by the ionosphere. That quantity is lower than the MUF for 3000 km path lengths due to ionospheric dynamics. While MUF is useful for long-distance communications, \(f_{0F2}\) is useful for local near-vertical incident skywave (NVIS) communications, where HF signals are aimed at the ionosphere and reflected off at a nearly-vertical angle (hence the name) to provide local communications without interference by local topography.