MUF - Maximum Usable Frequency
LUF - Lower Usable Frequency


Although ionosphere can reflect radio waves, this does not happen always, for every frequency or trasmiting angle.
 
At a given time we could see the radio waves of a certain frequency absorbed by ionosphere, while others, of higher frequency, are reflected and others pass through and are lost in space.
 
In order to usefully plan radio comunications, it is thus very important to know what minimum and maximum frequencies permit usable ionosphere reflections, for a given time and distance. These two values are defined as LUF, Lower Usable Frequency, and MUF, Maximum Usable Frequency.
 
The part or ionosphere of utmost interest for radio amateurs is layer F, with a single jump distance of about 4000 km.
 
Some university institutes, worldwide, periodically produce MUF maps taking into account the actual state of ionosphere, which is alto tested by transmitting radio pulses.


A typical MUF map, click to enlarge

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