The lowest usable high frequency (LUF), in

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

transmission, is a

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

in the HF band at which the received field intensity is sufficient to provide the required signal-to-noise ratio for a specified time period, e.g., 0100 to 0200 UTC, on 90% of the undisturbed days of the month. Any frequency lower than this is not able to fulfill those requirements, while higher frequencies usually yield better result until the maximum usable frequency is reached. The amount of energy absorbed by the lower regions of the

ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...

(D region, primarily) directly impacts the LUF.

Sources

Federal Standard 1037C Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms, is a United States Federal Standard issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, ...

Radio frequency propagation {{telecomm-stub

See also

Sources