Garmin GMA 340 Pilot's Manual - Page 7

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Garmin GMA 340 Pilot's Manual

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.
Audio
Frequency
400
1300
3000
The marker beacon audio level is aligned at the factory to produce its rated audio output.
However, the audio output level is adjustable by your
The GMA 340' s marker beacon receiver controls are located on the left side of the front panel
(1-4). 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 initially selected by pressing the MKR/mute button (2). If no marker bea-
con signal is received, then a second button press 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 deselect-
ed. The button' s LED will remain lit to indicate that the source is still selected. When the current
marker signal is no longer received, the audio is automatically un-muted. While in the muted state,
pressing the MKR/mute button deselects the marker audio. The button' s LED will extinguish to indi-
cate that the marker audio is no longer selected.
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 Keying
installing agency
Lamp Actuated
Blue (Outer)
Amber (Middle)
White (Airway/Inner)
.
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