Locator Beacons are low powered NDBs used for terminal procedures and approaches, with useful ranges of between 10 and 25 nm. NDBs are non-directional beacons that transmit a simple carrier wave with a modulation to overlay the morse code identifier. The ADF (Automatic Direction Finder) is the equipment in the cockpit which points a needle directly towards the NDB in question, by finding out which direction the radio wave arrived from.
NDBs operate between 190 and 1750 kHz, which spans both the LF (Low Frequency, 30 - 300 kHz) and MF (Medium Frequency, 300 - 3000 kHz) frequency bands.
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