P i l o t’s G u i d e
Front Panel Controls
1.Marker Beacon Lamps
2.
Marker Beacon Receiver Audio Select/Mute Button 3.
Marker Beacon Receiver Sensitivity Indicator LED.4.
Marker Beacon Receiver Sensitivity Selection Button
5.
Unit On/Off, Pilot Intercom System (ICS) Volume 6.
Pilot ICS Voice Activated (VOX) Intercom Squelch Level 7.
Copilot and Passenger ICS Volume Control (Pull out for Passenger Volume)8.
Copilot/Passenger VOX Intercom Squelch Level 9.Crew Isolation Intercom Mode Button 10.Pilot Isolation Intercom Mode Button
11.Passenger Address (PA) Function Button
12.Speaker Function Button
13.Transceiver Audio Selector Buttons (COM1, COM2, COM3)
14.Transmitter (Audio/Mic) Selection Buttons 15.Split COM Button
16.Aircraft Radio Audio Selection Buttons (NAV1, NAV2, DME, ADF)
17.Annunciator Test Button
18.Locking Screw Access
19.  Photocell - Automatic Annunciator Dimming
1
MKR
BCN ICS
COM/
NAV
On, Off, and Fail-Safe Operation
The GMA 340 is powered off when the left small knob (5) is rotated fully CCW into the detent. To turn the unit on, rotate the knob clockwise past the click.  The knob then functions as the pilot ICS volume control.  A fail-safe circuit connects the pilot’s headset and microphone directly to COM1 in case power
is interrupted or the unit is turned off.
Lighting
LED button annunciator and marker beacon lamp intensity are controlled automatically by a built-in photocell on the front panel.  Nomenclature backlighting is controlled by the aircraft dim-mer buss.
Transceivers
Audio level is controlled by the selected COM radio volume controls.
Selection of either COM1, COM2, or COM3 for both MIC and audio source is accomplished by pressing either COM1 MIC, COM2 MIC, or COM3 MIC (14).  The active COM audio is always heard on the headphones.
Additionally, each audio source can be selected independently by pressing COM1, COM2, or COM3 (13).  When selected this way, they remain active as audio sources regardless of which trans-ceiver has been selected for microphone use.
When a microphone is keyed, the active transceiver’s MIC button LED blinks approximately once per second to indicate that the radio is transmitting.
Split COM
Pressing the COM 1/2 button (15) activates the split COM function.  When this mode is active, COM1 is dedicated solely to the pilot for MIC/audio while COM2 is dedicated to the copilot for MIC/audio.  The pilot and copilot can simultaneously transmit in this mode over separate radios. Both pilots can still listen to COM3, NAV1, NAV2, DME, ADF, and MKR as selected.  The split COM mode is cancelled by pressing the COM 1/2 button a second time.
When in the split COM mode the copilot may make PA announcements while the pilot contin-ues using COM1 independently.  When the PA button is pressed after the split com mode is acti-vated, the copilot’s mic is output over the cabin speaker when keyed.  A second press of the PA but-ton returns the copilot to normal split COM operation.
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If the COM radios utilize a “transmit interlock” system, the split COM function
may require that this feature is enabled.  Refer to the radio installation manual
for guidance.  GARMIN makes no expressed or implied guarantees regarding
the suitability of the split COM feature in a given installation.
COM Swap Function
The GMA 340 allows the use of a remote mounted switch (typically on the yoke) to alternately transfer the active microphone back and forth between COM1 and COM2.  Pressing the remote switch will have no effect if COM3 is the active transceiver.  Ask your installing agency for details. Aircraft Radios & Navigation
Audio level is controlled by the selected NAV radio volume control.
Pressing NAV1, NAV2, DME, ADF (16), or MKR (2) (see MKR Beacon Receiver) selects each audio so
urce.  A second button press deselects the audio.  In addition, the GMA 340 provides inputs for an unswitched aircraft radio (TEL RINGER) and an un-muted, unswitched aircraft radio (ALT WRN).
Speaker Output
Pressing the SPKR button (12) selects the aircraft radios over the cabin speaker.  The speak-er output is muted when a COM microphone is keyed.  The GMA 340 speaker output level can be adjusted by your installing agency.
PA Function
The PA mode is activated by pressing the PA button (11).  Then, when either the pilot’s or copilot’s microphone is keyed, the corresponding mic audio is heard over the cabin speaker.  If the SPKR button is also active, then any selected speaker audio is muted while the microphone is keyed. The SPKR button does not have to be previously active in order to use the PA function.  Pilot and copilot PA microphone speaker levels are adjustable by your installing agency.
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Auxiliary Entertainment Inputs
The GMA 340 provides two stereo entertainment inputs: MUSIC1 and MUSIC2.  MUSIC1 is soft-muted during all aircraft radio activity and normally during ICS activity.  MUSIC2 is a non-muted input.  These inputs are compatible with popular portable entertainment devices such as cas-sette tape or CD players.  The headphone outputs of these devices are used and plugged into MUSIC1 or MUSIC2.  T wo 3.5 mm stereo phone jacks should be installed in a convenient location for this purpose.  MUSIC1 and MUSIC2 have characteristics that are affected by the active intercom mode.  Refer to the table on page 5.
Intercom System (ICS)
Intercom volume and squelch (VOX) are adjusted using the following front panel knobs:
• LEFT SMALL KNOB—Unit ON/OFF power control and Pilot ICS volume.  Full CCW detent position is OFF.
• LEFT LARGE KNOB—Pilot ICS mic VOX squelch level.  CW rotation increases the amount of mic audio (VOX level) required to break squelch.  Full CCW is the “HOT MIC” position (no squelch).
• RIGHT SMALL KNOB—IN position: Copilot ICS volume. OUT position: Passenger ICS volume.
• RIGHT LARGE KNOB—Copilot and passenger mic VOX squelch level.  CW rotation increases the amount of mic audio (VOX level) required to break squelch.  Full CCW is the “HOT MIC” position.
Each of the six microphone inputs have dedicated VOX circuits to ensure that only the active microphone(s) is/are heard when squelch is broken.  This represents a vast improvement over the party-line systems and reduces the amount of background noise in the headphones during cockpit communications.  After the operator has stopped talking, the intercom channel remains momentar-ily open to avoid closure between words or normal pauses.
The GM A 340 provides three intercom modes: PILOT, CREW and ALL.  M ode selection is accomplished using the PILOT and/or CREW buttons.  Pressing a mode button activates the corre-sponding ICS mode.  Pressing again deactivates the mode.  The ALL mode is active when neither PILOT nor CREW LEDs are lit.  To switch from PILOT to CREW mode, press the CREW button; from CREW to PILOT, press the PILOT button.  An LED ON indicates the isolation mode is active.
headset
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