SECTION 7
CESSNA
AIRPLANE & SYSTEMS DESCRIPTIONS
MODEL 172RG
selector switch in the PHONE position) to be heard on both
the airplane speaker and the headset simultaneously.
AUTO AUDIO SELECTOR SWITCH
The audio control panel used with three transmitters incorporates a
three-position toggle switch, labeled AUTO, which is provided to automat-
ically match the audio of the appropriate NAV/COM receiver to the
selected transmitter. To utilize this automatic feature, leave all NAV/ COM
audio selector switches in the center (OFF) position, and place the AUTO
selector switch in either the SPEAKER or PHONE position, as desired.
Once the AUTO selector switch is positioned, the pilot may then select any
transmitter and its associated NAV/COM receiver audio simultaneously
with the transmitter selector switch. If automatic audio selection is not
desired, the AUTO selector switch should be placed in the center (OFF)
position.
NOTE
If the NAV/COM audio selector switch corresponding to
the selected transmitter is in the PHONE position with the
AUTO selector switch in the SPEAKER position, all audio
selector switches placed in the PHONE position will
automatically be connected to both the airplane speaker
and any headsets in use.
ANNUNCIATOR LIGHTS BRIGHTNESS AND TEST SWITCH
The audio control panel used with either one or two transmitters
incorporates a three-position toggle-type switch to control the brightness
level of the marker beacon indicator lights (and certain other annunciator
lights associated with avionics equipment). When the switch is placed in
the center (DAY) position, the indicator lights will show full bright. When
this switch is placed in the up (NITE) position, the lights are set to a
reduced level for typical night operations and can be further adjusted
using the RADIO LT dimming rheostat knob. The down (TEST) position
illuminates all lamps (except the ARC light in the NAV indicators) which
are controlled by the switch to the full bright level to verify lamp opera-
tion.
SIDETONE OPERATION
Cessna radios are equipped with sidetone capability (monitoring of
the operator's own voice transmission). While adjusting sidetone, be
aware that if the sidetone volume level is set too high, audio feedback
(squeal) may result when transmitting.
7-44
1 July 1979
CESSNA
SECTION 7
MODEL 172RG
AIRPLANE & SYSTEMS DESCRIPTIONS
When the airplane has one or two transmitters, sidetone is provided in
both the speaker and headset anytime the COM AUTO selector switch is
utilized. Placing the COM AUTO selector switch in the OFF position will
eliminate sidetone. Sidetone internal adjustments are available to the pilot
through the front of the audio control panel (see figure 7-11). Adjustment
can be made by removing the appropriate plug-button from the audio
control panel (left button for headset adjustment and right button for
speaker adjustment), inserting a small screwdriver into the adjustment
potentiometer and rotating it clockwise to increase the sidetone volume
level.
When the airplane has three transmitters, sidetone will be heard on
either the speaker or a headset as selected with the AUTO selector switch.
Sidetone may be eliminated by placing the AUTO selector switch in the
OFF position, and utilizing the individual audio selector switches. Adjust-
ment of speaker and headset sidetone volume can only be accomplished by
adjusting the sidetone potentiometers located inside the audio control
panel.
NOTE
Sidetone is not available on
HF
Transceivers (Types PT10-
A and ASB-125), when installed.
MICROPHONE-HEADSET INSTALLATIONS
Three types of microphone-headset installations are offered. The
standard system provided with avionics equipment includes a hand-held
microphone and separate headset. The keying switch for this microphone
is on the microphone. Two optional microphone-headset installations are
also available; these feature a single-unit microphone-headset combina-
tion which permits the pilot to conduct radio communications without
interrupting other control operations to handle a hand-held microphone.
One microphone-headset combination is offered without a padded headset
and the other version has a padded headset. The microphone-headset
combinations utilize a remote keying switch located on the left grip of the
pilot's control wheel. The microphone and headset jacks are located on the
left side of the instrument panel. Audio to all three headsets is controlled
by the individual audio selector switches and adjusted for volume level by
using the selected receiver volume controls
.
NOTE
When transmitting, the pilot should key the microphone,
place the microphone as close as possible to the lips and
speak directly into it.
1 July 1979
7-45
