Editing Very low frequency (section)

=== Navigation beacons and time signals ===
Due to its long propagation distances and stable phase characteristics, during the 20th&nbsp;century the VLF band was used for long range [[hyperbolic navigation|hyperbolic]] [[radio navigation]] systems which allowed ships and aircraft to determine their geographical position by comparing the phase of radio waves received from fixed VLF [[navigation beacon]] transmitters.

The worldwide [[Omega (navigation system)|Omega]] system used frequencies from 10 to 14&nbsp;kHz, as did Russia's [[Alpha (navigation)|Alpha]].

VLF was also used for [[standard time and frequency signal|standard time and frequency]] broadcasts. In the US, the [[time signal]] station [[WWVL]] began transmitting a 500&nbsp;W signal on 20&nbsp;kHz in August&nbsp;1963. It used frequency-shift keying ([[Frequency-shift keying|FSK]]) to send data, shifting between 20&nbsp;kHz and 26&nbsp;kHz. The WWVL service was discontinued in July&nbsp;1972.