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Revision 1, June 2009
202-780-0429
Note: Because the telephone uses an intercom circuit, all stations on
that circuit will lose intercom capability when the telephone is in use.
Marker Beacon
The Marker Beacon Receiver uses
visual and audio indicators to alert
you when the aircraft passes over a
75 MHz transmitter.
The Blue lamp, labeled "O," is the
Outer Marker lamp and has an asso-
ciated 400-Hertz 'dash' tone. The lamp and tone will be keyed at a rate of
two tones/flashes per second when the aircraft is in the range of the Outer
Marker Beacon.
The Amber lamp, labeled "M," is the Middle Marker lamp and is coupled
with a 1300-Hertz tone. It is keyed alternately with short 'dot' and long
'dash' bursts at 95 combinations per minute.
The White lamp, labeled "I," is the Inner marker and has a 3000-Hertz 'dot'
tone. The lamp and tone will be keyed at a rate of six times per second.
The audio from the Marker Beacon Receiver can be heard by selecting the
"MKR" push-button switch. To adjust the volume level, there is a service
adjustment located on the top of the unit.
A three-position switch is used to set the receiver sensitivity and to test the
indicator lamps. Use "
HI
" sensitivity initially. This allows you to hear the
outer marker beacon about a mile out. Then select the “
LO
” sensitivity to
give you a more accurate location of the Outer Marker. The momentary
down switch position is marker test, labeled "T/M" and illuminates all three
lamps simultaneously to assure the lamps (internal and external) are in
working order. TST does not activate MM sense output.
Pressing the marker mode select down (to “T/M”) will cause the marker
audio to mute for that beacon. The next beacon received will re-activate the
audio.