Definition
A range of radio frequencies used in aviation navigation, where low frequency (LF) covers 30 to 300 kHz and medium frequency (MF) covers 300 to 3,000 kHz. These bands are used by non-directional beacons (NDBs) and automatic direction finder (ADF) equipment because their long wavelengths follow the curvature of the Earth and travel beyond line of sight.
Plain English
A slice of the radio spectrum at the lower end of the dial. Aviation uses these frequencies for older-style navigation beacons that an aircraft's ADF needle points to.
Context Anchor
Seen in instrument navigation discussions when a pilot reads or tunes the frequency for certain ground-based navigation signals.
Derivation
Frequency comes from a Latin word meaning repeated occurrence. In radio, it means how many times a radio wave repeats each second. Low and medium identify the lower ranges of that radio scale.
Why Pilots Care
These signals travel farther than higher-frequency signals and can be received over water or remote areas where line-of-sight navigation is unavailable.
Grounding Statement
If a navigation station is listed at a number such as 365 kilohertz, it is operating in the low or medium frequency range.
Intuition Check
Low or medium frequency does not mean the signal is weak or only moderately useful. Here it names a specific radio-frequency range: 190 to 535 kilohertz.
Example Sentence 1
The NDB the pilot was tracking transmitted on a low or medium frequency, so the ADF needle was susceptible to thunderstorm interference.
Example Sentence 2
Over remote terrain, low or medium frequency signals provided reliable navigation when other aids were out of range.