Marker Beacon

Function

• The marker beacon system is a radio navigation aid which determines the distance between the aircraft and the runway threshold.

• The system provides visual and aural indications of the passage of the aircraft over the marker transmitters located on the ground.

 Operation

•       MKR beacon system consists of 3 transmitters on ground (outer, middle and inner markers) and a receiver at the aircraft.

 

•        All marker stations transmit on a basic radio frequency carrier of 75 MHZ. The thing that distinguishes one from the other is the frequency of the audio tone which modulates the carrier frequency (AM modulation).
•       The outer marker transmits 400 HZ tone, 
•      The middle marker transmits 1300 HZ tone and
•      The inner marker transmits 3000 HZ tone.

 

•      When the aircraft passes through the beam of a marker, the modulating frequency is detected.

•       Then, the system provides aural and visual indications to the flight crew to indicate passage over a marker beacon transmitter.

 

• Appropriate light will flash and an audible sound may be heard.

1- Antenna.

2- 75 MHZ filter.

3- RF amplifier and detector : comes whatever audio tone has

 modulated the carrier.

4-  Audio filters : to discriminate audio tones.

5- Audio amplifier : the tones with the Morse code for identifying a station are available through the audio amplifier to the cockpit interphone system.