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The stations known as NDB (Non-Directional Beacon)
are widely used in aeronautical and maritime services.
The transmissions are realized continuously in continuous wave (CW),
There were allocated two frequency ranges for these stations:
190-535 kHz and 1600-1800 kHz.
It is determined a tone for the note to be emitted by the identifier, with its
value varying depending on the country (in Brasil, the tone is 1020 Hz).
The NDB represents a "mark" of radio signals in CW.
In radioshipping a NDB determines a relative position or a objective.
In the first case the ship or airplane passes over a reference
(being reported as "passing through" or "passing over").
In the second case, the mark is the end point of the route.
NDB's are operated by several entities:
Air Force, Navy, petroleum companies, particulars, etc.
Unless in certain cases (as in militar operations) NDB's operate continuously.
The signals are received in the aircraft or ship by a specified on-board system,
as a AM receiver with VFO.
The signals consist basically of letters identifying the station,
having up to four characters.
In Brazil aeronautic stations are usually identified by three characters,
while maritim stations utilize two characters.
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Click here
if you wish to hear a sample audio from a Brazilian NDB
(in this case, the aeronautic station CAX,
located in Duque de Caxias, RJ, Brazil).
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