radio signals in the low to medium
frequency band of 190 Khz. to 1750
Khz. It was widely used today. It has
the major advantage over VOR
navigation in the reception is not limited to line of sight distance. The
ADF signals follow the curvature of the
earth. The maximum of distance is
depend on the power of the beacon.
The ADF can receives on both AM radio
station and NDB (Non-Directional Beacon). Commercial AM radio stations
broadcast on 540 to 1620 Khz. Non-
Directional Beacon operate in the
frequency band of 190 to 535 Khz.
ADF COMPONENTS
• ADF Receiver : pilot can tune the station desired and to select the mode
of operation. The signal is received,
amplified, and converted to audible
voice or morse code transmission and
powers the bearing indicator.
• Control Box (Digital Readout Type) : Most modern aircraft has this type of
control in the cockpit . In this
equipment the frequency tuned is
displayed as digital readout. ADF
automatically determines bearing to
selected station and it on the RMI.
• Antenna : The aircraft consist of two antennas. The two antennas are called
LOOP antenna and SENSE antenna. The
ADF receives signals on both loop and
sense antennas. The loop antenna in common use today is a small flat
antenna without moving parts. Within
the antenna are several coils spaced at
various angles. The loop antenna
sense the direction of the station by
the strength of the signal on each coil but cannot determine whether the
bearing is TO or FROM the station. The sense antenna provides this latter information.
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