From International Dictionary of Marine Aids to Navigation
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A continuous wave, medium frequency (300 kHz region) long range directional radio beacon producing a number of radial equi-signal zones which shift in azimuth at a fixed rate and are separated by zones of dot and dash signals.

The bearing of a mobile station with respect to the beacon is determined by a count of the dot and dash signals within each respective zone.

The ambiguity can be resolved by the use of a D.F. receiver.

Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)


diameter at the waterline (m)

change in the value of a term

Solar declination angle (in degrees)

Forward amplitude




International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM