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MUF is a median frequency, defined as the highest frequency at which skywave communication is possible 50% of the days in a month, as opposed to the lowest usable high frequency (LUF) which is the frequency at which communication is possible 90% of the days, and the frequency of optimum transmission (FOT). Typically the MUF is a predicted number.
The usable frequencies change from day to night, because sunlight causes the lowest layer of the ionosphere, called the D layer, to increase, causing attenuation of low frequencies during the day [4] while the maximum usable frequency (MUF) which is the critical frequency of the F layer rises with greater sunlight.
The maximum usable frequency regularly drops below 10 MHz in darkness during the winter months, while in summer during daylight it can easily surpass 30 MHz. It depends on the angle of incidence of the waves; it is lowest when the waves are directed straight upwards, and is higher with less acute angles.
Frequencies above 10 MHz (wavelengths shorter than 30 meters) typically propagate most efficiently during the day. Frequencies lower than 3 kHz have a wavelength longer than the distance between the Earth and the ionosphere. The maximum usable frequency for skywave propagation is strongly influenced by sunspot number.
This technology allows meteorologists to detect the highest frequency that can be vertically returned [31] 24 hours in advance with accuracy of 8-13% periods with limited disturbance. PropMan, created by K. Davies in the early 1970s is a program that contains the ionospheric prediction code (IONSTORM), to forecast maximum usable frequencies ...
During the daytime when sunspot activity is at a maximum, the F2 layer can become intensely ionized due to radiation from the sun. When solar activity is sufficiently high, the maximum usable frequency (MUF) increases, hence the ionisation density is sufficient to reflect signals well into the 30-60 MHz VHF spectrum. Since the MUF progressively ...
Seasonal flu activity is elevated across most of the country, according to the latest reports from the Centers for Disease Control and Prevention, and experts say this is expected to continue for ...
Frequency of optimum transmission (FOT), in the transmission of radio waves via ionospheric reflection, is the highest effective (i.e. working) frequency that is predicted to be usable for a specified path and time for 90% of the days of the month. The FOT is normally just below the value of the maximum usable frequency (MUF). In the prediction ...