Garmin 340, Pilot'S Manual

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8
Marker Beacon Receiver
The marker beacon is used as part of an ILS approach, and in certain instances, to identify an airway.
In addition to the normal marker beacon functions, the GMA 340 provides an audio muting function. The
lamps illuminate, and an associated keyed-tone is heard when MKR audio is selected, when the aircraft
passes over a 75 MHz marker beacon transmitter.
The lamp and audio keying for ILS approach operation are summarized below:
The marker beacon audio level is aligned at the factory to produce its rated audio output. However,
the output level is adjustable by your avionics installing agency.
The GMA 340’s marker beacon receiver controls are located on the left side of the front panel (1
through 4). The SENS button selects either high or low sensitivity as indicated by the HI or LO LED
being lit. Low sensitivity is used on ILS approaches while high sensitivity allows operation over airway
markers or to get an earlier indication of nearing the outer marker during an approach.
The marker audio is selected initially by pressing the MKR/mute button (2). If no marker beacon
signal is received, then pressing again will deselect the marker audio. This operation is similar to
selecting any other audio source on the GMA 340. However, if the second button press occurs while a
marker beacon signal is received, then the marker audio is muted but not deselected. The button’s LED
will remain lit to indicate that the source is still selected.
The GMA 340’s
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function then monitors the marker signal and automatically unmutes
the audio when the current marker signal is no longer being received.
In all cases, the marker beacon lamps operate independently of any audio selection and cannot be
turned off. The GMA 340 can drive external marker lamps if required.
Audio
Frequency
Audio Keying Lamp Actuated
400 Hz
Blue (Outer)
1300 Hz
Amber (Middle)
3000 Hz White (Airway/Inner)