CESSNA AIRCRAFT COMPANY FOR TRAINING USE ONLY
MODEL 152 7-29
The transmitter selector switch is labeled TRANS, and has two positions. When two transmitters are
installed, it is necessary to switch the microphone to the radio unit the pilot desires to use for
transmission. This is accomplished by placing the transmitter selector switch in the position
corresponding to the radio unit which is to be used. The up position selects the upper transmitter and
the down position selects the lower transmitter.
The installation of Cessna radio equipment provides certain audio back-up capabilities and transmitter
selector switch functions that the pilot should be familiar with. The audio amplifier in the NAV/COM
radio is required for speaker and transmitter operation. The amplifier is automatically selected, along
with the transmitter, by the transmitter selector switch. As an example, if the number 1 transmitter is
selected, the audio amplifier in the associated NAV/COM receiver is also selected, and functions as the
amplified for ALL speaker audio. In the event the audio amplifier in use fails, as evidenced by loss of all
speaker audio and transmitting capability of the selected transmitter, select the other transmitter. This
should re-establish speaker audio and transmitter operation. Since headset audio is not affected by
audio amplifier operation, the pilot should be aware that, while utilizing a headset, the only indication of
audio amplifier failure is loss of the selected transmitter. This can be verified by switching to the
speaker function.
The speaker-phone switches determine whether the output of the receiver in use is fed to the
headphones or through the audio amplifier to the speaker. Place the switch for the desired receiving
system either in the up position for speaker operation or in the down position for headphones. The
center OFF position will remove receiver output to either headphones or the speaker.
Figure 7-10. Audio Control Panel
Airplanes equipped with any radio other than the Cessna 300 Nav/Com (Type RT-385A) will not have
sidetone capability (monitoring of the operator’s own voice transmission). If the airplane is equipped
with a Cessna 300 Nav/Com (Type RT-385A), the radio will have sidetone capabilities and the audio
control panel will include a speaker sidetone volume control knob as illustrated in figure 7-10. Sidetone
will be heard on either the airplane speaker or a headset as selected with the speaker-phone selector
switches. When the speaker position is selected, sidetone audio volume may be controlled by rotating
the SIDETONE VOL control knob clockwise to increase audio volume and counterclockwise to decrease
it. When headphones are in use, sidetone volume cannot be adjusted.
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