Lowest usable high frequency
The lowest usable high frequency (LUF), in radio transmission, is that frequency 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. The amount of energy absorbed by the lower regions of the ionosphere (D region, primarily) directly impacts the LUF.
|This article related to telecommunications is a stub. You can help Wikipedia by expanding it.|