_________________________________________________________________
GMA
347
Maintenance
Manual
Page
2
‐
1
190
‐
00325
‐
02
Rev.
A
SECTION
2
AUDIO
PANEL
DESCRIPTION
The
GMA
347
is
a
horizontally
oriented,
panel
‐
mounted
audio
control
panel
and
marker
beacon
system.
Microcontroller
circuitry
processes
front
panel
key
commands,
controls
annunciator
operation,
and
processes
input/output
and
communication
information.
A
prominent
design
feature
of
the
audio
panel
is
MASQ™
(Master
Avionics
Squelch)
processing.
When
no
airplane
radio
activity
is
detected
by
the
GMA
347,
the
amount
of
ambient
background
noise
is
reduced
by
MASQ™.
2.1
UNIT
FEATURES
2.1.1
Intercom
System
The
audio
panel
features
a
six
‐
position
intercom
system
(ICS)
with
electronic
cabin
noise
de
‐
emphasis,
two
stereo
music
inputs,
and
combined
pilot,
copilot,
and
passenger
volume
controls.
The
intercom
provides
four
selectable
modes
of
isolation
(All,
Crew,
Pilot,
Copilot).
A
pilot
‐
selectable
cabin
speaker
output
can
be
used
to
listen
to
the
selected
aircraft
radios
or
to
broadcast
PA
announcements.
The
PA
function
is
pilot
selectable.
2.1.2
Digital
Voice
Recorder
The
audio
panel
contains
a
digital
voice
recorder
with
playback
capability
providing
up
to
two
and
a
half
minutes
of
recording.
The
playback
feature
is
controlled
by
pressing
the
PLAY
button
or
a
remote
mounted
switch.
Recording
is
automatic
when
a
COM
signal
is
received.
The
recorder
can
be
disabled
using
an
external
switch.
2.1.3
Marker
Beacon
Receiver
A
marker
beacon
receiver
with
dual
sensitivity,
audio
muting,
and
automatic
re
‐
arming
is
incorporated
in
the
audio
panel.
Receiver
operating
voltage
range
is
14/28
VDC.
2.1.4
SmartMute™
The
marker
audio
is
selected
initially
by
pressing
the
MKR/MUTE
button.
If
no
marker
beacon
signal
is
being
received,
then
pressing
button
2
again
will
deselect
the
marker
audio.
This
operation
is
similar
when
selecting
any
other
source
on
the
GMA
347.
However,
if
the
second
button
press
occurs
when
a
marker
beacon
signal
is
being
received,
then
the
marker
audio
is
muted
muted
but
not
deselected.
The
button’s
LED
will
remain
lit
to
indicate
that
the
source
is
still
selected.
The
GMA
347’s
SmartMute™
function
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.
