.
NAV 1, NAV 2, MKR (marker), ADF, AUX (auxiliary), and DME latch in to select the related audio when you press them. The button un-latches when you press it again.

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) Speaker amplifier. The SPR (speaker) is a 'latched' type switch. When the button is 'latched', it will place all selected audio on the cockpit speaker. The button un-latches when you press it again.
) Key Click. You can select a ‘click' to occur over the audio system when you press a button. Press and hold both the COM 1 and COM 2 buttons for 5 seconds to select the key click. Press and hold both the COM 1 and COM 2 buttons again for 5 seconds to de-select the key click.
Each button has a green LED. The green LED comes ON when you select the button.
% (3) KMA 28 Intercom Functions
) VOX-Squelch. The system has an automatic volume control for each microphone. The circuit only operates when the system detects speech in the microphone. The system blocks continuos tones.
) VOL Control. The VOL control knob adjusts the loudness of the intercom for the pilot and co-pilot. It has no effect on the radio levels.
) Intercom Modes. The lower switch on the left side is a three-position mode switch. It has the following positions:
.
ISO (up position). The pilot is connected only to the airplane radio. He is isolated from the intercom. The co-pilot can communicate with the passengers but the co-pilot can not make or hear transmissions on the airplane radio.

.
ALL (mid position). The pilot, co-pilot and passengers can all hear the radio. Both the pilots and the passengers can communicate on the intercom.

.
CREW (down position). The pilot and co-pilot are connected on one intercom channel while the passengers are on a separate and independent channel. The pilot and co-pilot are connected to the airplane radio. Passengers can continue to communicate with themselves without disturbing the pilot and co-pilot.

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% (4) KMA 28 Marker Beacon Receiver Operation
The marker beacon receiver has visual and audio indicators to show when the airplane passes over a beacon transmitter. Select the MKR push-button to hear the audio from the marker beacon receiver.
A three-position switch sets the receiver sensitivity. It also has a test function:
) HI (high sensitivity, up position). The receiver will detect the outer marker beacon approximately 1 mile out.
) LO (low sensitivity, middle position). The receiver will detect the marker beacon more accurately.
) T/M (test, momentary down position). The spring-loaded down position tests all 3 lights. If you push the switch down while receiving a beacon signal, it mutes the marker tone temporarily.
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% C. Garmin GMA 340 Audio Panel
% (1) GMA 340, General
% Figure 3 shows the Garmin GMA 340 Audio Panel. It is mounted above the COM/NAV/GPS #1 % set in the avionics rack in the instrument panel, see Chapter 31.
% The GMA 340 provides flexibility in switching up to three microphone and audio transceiver % communication inputs plus NAV 1, NAV 2, ADF, DME and marker audio. The GMA 340 % includes a voice activated (VOX) intercom system and a three lamp marker beacon receiver % and display.
% The VOX intercom uses rotary knobs for volume and squelch adjustment while selection of all % other functions is accomplished with the use of push-buttons.
% If the power to the system fails, (or if the selector panel is turned off), an Emergency Mode % connects the pilot's headset to COM 1.
% Marker HI and LO and button annunciation is accomplished with LED devices. Front panel % backlighting of button function, squelch and volume control knobs is provided by LED's % controlled by the airplane lighting bus.
　
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