SECTION 7
CESSNA
AIRPLANE & SYSTEMS DESCRIPTIONS
MODEL 172RG
operational features of both audio control panels are similar and are
discussed in the following paragraphs.
TRANSMITTER SELECTOR SWITCH
When the avionics package includes a maximum of two transmitters, a
two-position toggle-type switch, labeled XMTR, is provided to switch the
microphone to the transmitter the pilot desires to use. If the airplane
avionics package includes a third transmitter, the transmitter selector
switch is a three-position rotary-type switch, labeled XMTR SEL. The
numbers 1, 2, or 1, 2 and 3 adjacent to the selector switches correspond to
the first, second and third (from top to bottom) transmitters in the avionics
stack. To select a transmitter, place the transmitter selector switch in the
position number corresponding to the desired transmitter.
The action of selecting a particular transmitter using the transmitter
selector switch simultaneously selects the audio amplifier associated with
that transmitter to provide speaker audio. For example, if the number one
transmitter is selected, the audio amplifier in the number one NAV/COM
is also selected and is used for ALL speaker audio. In the event the audio
amplifier in use fails, as evidenced by loss of all speaker audio, selecting
an alternate transmitter will reestablish speaker audio using the alternate
transmitter audio amplifier. Headset audio is not affected by audio
amplifier operation.
AUDIO SELECTOR SWITCHES
Both audio control panels (see figure 7-11) incorporate three-position
toggle-type audio selector switches for individual control of the audio
from systems installed in the airplane. These switches allow receiver
audio to be directed to the airplane speaker or to a headset, and heard
singly or in combination with other receivers. To hear a particular
receiver on the airplane speaker, place that receiver's audio selector
switch in the up (SPEAKER) position. To listen to a receiver over a
headset, place that receiver's audio selector switch in the down (PHONE)
position. The center (OFF) position turns off all audio from the associated
receiver.
NOTE
Volume level is adjusted using the individual receiver
volume controls on each radio.
A special feature of the audio control panel used when one or two
transmitters are installed is separate control of NAV and COM audio from
the NAV/COM radios. With this installation, the audio selector switches
labeled NAV, 1 and 2 select audio from the navigation receivers of the
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1 July 1979
CESSNA
SECTION 7
MODEL 172RG
AIRPLANE & SYSTEMS DESCRIPTIONS
NAV/COM radios only. Communication receiver audio is selected by the
switches labeled COM, AUTO and BOTH. Description and operation of
these switches is described in later paragraphs.
When the audio control panel for three transmitters is installed, audio
from both NAV and COM frequencies is combined, and is selected by the
audio selector switches labeled NAV/COM, 1, 2 and 3.
COM AUTO AUDIO SELECTOR SWITCH
The audio control panel used with either one or two transmitters
incorporates a three-position toggle switch, labeled COM AUTO, which is
provided to automatically match the audio of the appropriate NAV/COM
communications receiver to the transmitter selected by the transmitter
selector switch. When the COM AUTO selector switch is placed in the up
(SPEAKER) position, audio from the communications receiver selected by
the transmitter selector switch will be heard on the airplane speaker.
Switching the transmitter selector switch to the other transmitter auto-
matically switches the other communications receiver audio to the
speaker. This automatic audio switching feature may also be utilized when
listening on a headset by placing the COM AUTO switch in the down
(PHONE) position. If automatic audio selection is not desired, the COM
AUTO selector switch should be placed in the center (OFF) position.
COM BOTH AUDIO SELECTOR SWITCH
The audio control panel used with either one or two transmitters
incorporates a three-position toggle switch, labeled COM BOTH, which is
provided to allow both COM receivers to be monitored at the same time. For
example, if the COM AUTO switch is in the SPEAKER position, with the
transmitter selector switch in the number one transmitter position,
number one communications receiver audio will be heard on the airplane
speaker. If it is also desired to monitor the number two communications
receiver audio without changing the position of the transmitter selector
switch, place the COM BOTH selector switch in the up (SPEAKER)
position so that the number two communications receiver audio will be
heard in addition to the number one communications receiver audio. This
feature can also be used when listening on a headset by placing the COM
BOTH audio selector switch in the down (PHONE) position.
NOTE
The combination of placing the COM AUTO switch in the
SPEAKER position and the COM BOTH switch in the
PHONE position (or vice versa) is not normally recom-
mended as it will cause audio from both communications
receivers (and any other navigation receiver with its audio
1 July 1979
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