A Non-Directional Beacon (NDB)
is a simple radio transmitter operating slightly below the AM
broadcast band, or in the Long-wave band. It sends out a continuous
signal, a "carrier," which is often modulated with
the station's identification, in Morse code. In this case, the
identification is LHI, or dit-dah-dit-dit dit-dit-dit-dit dit-dit
( .-.. .... .. ). This code helps the pilots confirm that they
are tuned to the right frequency. The pilots have on their flight
deck an instrument called the ADF or Automatic Direction Finder,
which simply consists of a needle which points toward the NDB.
Thus, the pilots can locate and track towards one. This is very
useful for a place, which during inclement weather can often
be very hard to visually pinpoint.
The NDB transmits medium frequency
band (190-540 kHz). It can be said that NDB is a Homing
Device. By plotting lines of position from two NDBs, the
pilots could find their direction. Using this information along
with the magnetic compass and the NDB receiver, the pilot could
determine the aircraft's bearing from the NDB.
The range of the beacon will
depend on the type of antenna used, the location of the installation;
the RF power supplied to the antenna, and the operating frequency
and ground conductivity. Effective coverage also varies according
to the time of day and the season of the year.
A NDB is classed according to its power output and usage:
The Low power radio beacon has a power of less than 50
watts (W),
The Medium power radio beacon has a power of 50 watts up
to 2,000 W;
The High power radio beacon has a power output of 2,000
W or more;
Navigation
is defined as the science of getting from one place to another
by continually determining position, course, and distance
covered. Of all the tasks the pilot has to perform during
a flight, navigation should be the least of concerns. Fortunately,
today’s pilot can rely on NAVigational AIDS. NAVAIDS
relieve the pilot of the navigation workload by providing
navigational data. NAVAIDS range from satellite positioning
systems such as Global Positioning Systems (GPS), to sophisticated
Very high frequency Omni Range (VOR), to the basic and most
widely used NAVAID, the Automatic Direction Finder/Non-Directional
Radio Beacon (ADF/NDB) systems.
An ADF/NDB system consists of two subsystems.
The first is the Automatic Direction Finder set. The ADF set
is used in an aircraft, or sometimes in a ground vehicle and
consists of a receiver that will pick up a radio signal in
the 190 KHz to 1800 KHz radio band. The ADF receiver utilizes
two antennas to intercept the radio signal and determine the
direction of that signal. This directional information is
displayed on an instrument that points to a compass heading
indicating the direction from the receiver to the source of
the radio signal.
The second subsystem of the ADF/NDB NAVAID
is the Non-Directional radio Beacon transmitter station. The
NDB produces the radio signal to which the ADF points. The
radio signal is broadcast in every direction at once, hence
it’s name, non-directional beacon.
Pilots can find out from an aeronautical
chart what radio station they should tune to in a particular
area. They can then tune their radio navigation equipment
to a signal from this station. A needle on the navigation
equipment tells the pilot where they are flying to or from
station, on course or not. Below is a sample of a pre-flight
plan chart detail.
Navigation
is defined as the science of getting from one place to another
by continually determining position, course, and distance
covered. Of all the tasks the pilot has to perform during
a flight, navigation should be the least of concerns. Fortunately,
today’s pilot can rely on NAVigational AIDS. NAVAIDS
relieve the pilot of the navigation workload by providing
navigational data. NAVAIDS range from satellite positioning
systems such as Global Positioning Systems (GPS), to sophisticated
Very high frequency Omni Range (VOR), to the basic and most
widely used NAVAID, the Automatic Direction Finder/Non-Directional
Radio Beacon (ADF/NDB) systems.
