automatic direction finder · like rdf units, most adf ... -the loop antenna sense the direction of...

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COMSOFT

COMSOFT GmbH | AMHS/AIS Qatar | April 2008

Automatic Direction Finder

COMSOFT GmbH | AMHS/AIM Qatar | April 2008

HOW DO I GET FROM HERE TO THERE?


Automatic Direction Finder

What is Automatic Direction Finder?

Automatic Direction Finder is navigational instrument use to point in

the direction of whatever station you tune-in that automatically and

continuously displays the relative bearing from the ship or aircraft to a

suitable radio station.

It is used as a means of identifying positions, receiving low and medium

frequency voice communications, homing, tracking, and for navigation

on instrument approach procedures.

ADF receivers are normally tuned to aviation or marine NDBs operating

in the LW band between 190 – 535 kHz. Like RDF units, most ADF

receivers can also receive medium wave (AM) broadcast stations.

The low/medium frequency navigation stations used by ADF include

non-directional beacons, ILS radio beacon locators, and commercial

broadcast stations.


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)

- the frequency tuned is displayed as digital readout.

- ADF automatically determines bearing to selected station and it on the RMI

- .


ADF COMPONENTS

Antenna

- The aircraft consist of two antennas

- LOOP antenna and SENSE antenna

- The ADF receives signals on both loop and sense antennas

- 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.

Bearing Indicator

- displays the bearing to station relative to the nose of the aircraft.

- Relative Bearing

- Magnetic Bearing


Non-directional Beacon

Ground equipment consists of a simple a.m. radio station

The NDB is the station on the ground that emits the signal that the ADF

tunes to. Its signal is emitted in all directions so it doesn’t matter where the aircraft's position is relative to the station, the ADF will still pick up

its signal.

the ADF always points to the NDB station.

NDBs may be located on the surface of airports, or may be within a few

miles from an airport. Sometimes they are co-located with the Outer

Marker in ILS approaches.


TYPE OF ADF INDICATOR

Fixed Compass Card

- It is fixed to the face of instrument and cannot rotate. 0 degree is

always straight up as the nose of aircraft.

Rotatable Compass Card

- The dial face of the instrument can be rotated by a knob


TYPE OF ADF INDICATOR

Single-Needle Radio Magnetic Indicator

- Radio Magnetic Indicator is an instrument that combines radio and

magnetic information to provide continuous heading , bearing ,

and radial information.

Dual-Needle Radio Magnetic Indicator

- the dual needle RMI is similar to single needle RMI except that it

has a second needle.


OPERATION of ADF

ADF operate in the low and medium frequency bands.

By tuning to NDB station or commercial AM radio stations.

NDB frequency and identification information may be obtained from

aeronautical charts and Airport Facility Directory.

The ADF has automatic direction seeking qualities which result in the

bearing indicator always pointing to the station to which it is tuned.

The easiest and perhaps the most common method of using ADF , is to

" home " to the station .


Purpose of ADF

The ADF may be in its design and function it is used by the pilot in flight for at

least five different purposes:

1. Position Fixing i.e. determining the aircraft's position

2. Enroute navigation

3. Instrument approaches

4. Holding

5. Indication on the commencement point of a more sophisticated instrument

approach


LIMITATIONS AND BENEFITS

Radio waves reflected by the ionosphere return to the earth 30 to 60

miles from the station and may cause the ADF pointer to fluctuate.

Mountains or cliffs can reflect radio waves, producing a terrain effect.

Shorelines can refract or bend low frequency radio waves as they pass

from land to water.

electrical storm is nearby, the ADF needle points to the source of lightning rather than to the selected station because the lighting sends

out radio waves.

The ADF is used for primary navigation over long distances in remote

areas.


Quiz

1. Define ADF? Answer. Automatic direction finder

2-3. What are the two common use of ADF? Answer. Homing to a station and Tracking from a station

4-7. What are the components of ADF?

Answer. ADF receiver, control box, antenna, bearing indicator

8. What is the allocated range frequencey band for ADF receiver?

Answer. 190-1750 Khz

9. Which of the following factors could cause an error of an ADF bearing of an NDB?

Answer. Night effect

a. Atmospheric scatter b. Phase interference

c. Night effect

d. None of the above

10. What gives the greatest error in ADF? Answer. Static interference from thunderstorms


Assignment

What is ADF system?

The ADF/NDB navigation system is one of the oldest air

navigation systems still in use today. It works from the most simple radio

navigation concept: a ground-based radio transmitter (the NDB) sends an

omnidirectional signal that an aircraft loop antenna receives. The result is a

cockpit instrument (the ADF) that displays the aircraft position relative to an NDB station, allowing a pilot to "home" to a station or track a course

from a station.

automatic direction finder · like rdf units, most adf ... -the loop antenna sense the direction of...

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