General description General
The marker beacon system has an antenna and a VOR/marker beacon (VOR/MB) receiver. The marker beacon function only operates in the VOR/MB receiver 1 position.
Operation
The marker beacon antenna receives the marker beacon signals. The signals go to the VOR/MB receiver 1. The VOR/MB receiver 1 supplies this data:
Marker beacon audio to the remote electronics unit (REU)
Marker beacon data to the common display system (CDS) display electronics unit (DEU)
Marker beacon data to the flight data acquisition unit (FDAU).
The displays show marker beacon data.
COMPONENT LOCATIONS
General
The marker beacon antenna is on the bottom of the fuselage. The VOR/MB receiver 1 is in the electronic equipment compartment E1-2.
The marker beacon data shows on these display units:
Left outboard display unit
right outboard display unit.
INTERFACES
Power
The VOR/marker beacon (VOR/MB) receiver 1 uses 115v ac power from the standby bus.
Antenna Interface
The marker beacon antenna sends radio frequency (RF) signals to the VOR/MB receiver 1.
PSEU
The proximity switch electronics unit (PSEU) supplies an air/ ground discrete signal to the VOR/MB receiver 1. The VOR/MB receiver uses this signal for these functions:
Prevent a test in the air
Count flight legs.
Audio Interface
The VOR/MB receiver 1 sends marker beacon audio to the remote electronics unit (REU). The REU supplies marker beacon audio to the flight compartment.
Marker Beacon Data
The VOR/MB receiver 1 supplies marker beacon data to the 1 and 2 common display system (CDS) display electronics units (DEU). The receiver also supplies marker beacon data to the FDAU.
VOR/MARKER BEACON RECEIVER
General
The VOR/marker beacon (VOR/MB) receiver has these two parts:
VOR receiver
Marker beacon receiver.
The marker beacon system operates in the VOR/MB receiver 1 position. The marker beacon receiver receives 75 MHz signals.
Test and Indications
You do a test of the these VOR/MB receiver 1 functions at the same time:
VOR function
MB function.
There is a test switch and two light emitting diodes (LEDs) on the front panel of the VOR/MB receiver.
Flight Fault Memory
The VOR/MB receiver has a nonvolatile flight fault memory.
Only shop personnel can read the memory.
MARKER BEACON ANTENNA
General
The marker beacon antenna receives signals from marker beacon ground stations.
Six screws hold the antenna to the fuselage.
DISPLAYS AND AUDIO OUTPUTS
General
When the airplane goes above a marker beacon transmitter, marker beacon data shows on the primary flight display (PFD).
If you want to hear marker beacon audio, you select the marker beacon audio on the audio control panel (ACP).
Display Types
OM shows when the airplane goes above the outer marker. The OM letters are cyan.
MM shows when the airplane goes above the middle marker.
The MM letters are yellow.
IM shows when the airplane goes above the inner marker, backcourse marker, or an airways marker. The letters IM are white.
NCD/Fail Display
If marker beacon data fails or is no computed data (NCD), the display does not show.
Audio General
The ACP supplies control signals to the remote electronics unit (REU). The REU uses the control signals to select the audio that goes to the flight interphone speakers and headsets.
Use the ACP to listen to marker beacon audio.
Audio Operation
You make these ACP selections to listen to marker beacon audio:
Push the marker beacon receiver volume control to make the marker beacon audio come on
Turn the marker beacon receiver volume control to change the volume level.
Audio Outputs
These are the marker beacon audio outputs:
Outer marker (OM) is 400 Hz, continuous dashes (- - - -)
Middle marker (MM) is 1300 Hz, alternate dots and dashes (-.-.-.-.-)
Inner marker (IM) is 3000 Hz, continuous dots (......)
Backcourse marker is 3000 Hz, continuous paired dots (.. .. .. ..)
Airways marker is 3000 Hz with the morse code. identifier for that station.
FUNCTIONAL DESCRIPTION
Marker Beacon Signal
The marker beacon antenna receives the 75 MHz signal and sends it to a 75 MHz filter in the VOR/marker beacon (VOR/MB) receiver 1. This filter tunes and rejects unwanted signals. The output goes to a radio frequency (RF) amplifier. A detector receives the amplifier output and sends the demodulated signal to three bandpass filters.
The bandpass filters are at 400 Hz, 1300 Hz, and 3000 Hz. The filters send the signals to an audio amplifier and to an input/ output (I/O) card. The audio amplifier sends audio tones to the REU. The I/O card sends data to the DEU and the flight data acquisition unit (FDAU).
The DEU shows marker beacon data on the PFDs.