Radio Selector Switches; Transmitter Selector Switch - Cessna 177 Cardinal Owner's Manual

power source can not be used as a source of power when checking
electronic components.
Just before connecting an external power source (generator type or battery
cart), the master switch should be turned "ON."
The ground service plug receptacle circuit incorporates a polarity reversal
protection. Power from external power source will flow only if the ground service
plug is correctly connected to the airplane. If the plug is accidentally connected
backwards, no power will flow to the airplane's electrical system, thereby
preventing any damage to electrical equipment.
The battery and external power circuits have been designed to completely
eliminate the need to "jumper" across the battery contactor to close it for charging a
completely "dead" battery. A special fused circuit in the external power system
supplies the needed "jumper" across the contacts so that with a "dead" battery and
an external power source applied, turning the master switch "ON" will close the
battery contactor.
STATIC PRESSURE ALTERNATE SOURCE VALVE
A static pressure alternate source valve may be installed below the left side
of the instrument panel in the static system for use when external static source is
malfunctioning. This valve also permits draining condensate from the static lines.

RADIO SELECTOR SWITCHES

RADIO SELECTOR SWITCH OPERATION
Operation of the radio equipment is normal as covered in the respective radio
manuals. When more than one radio is installed, an audio switching system is
necessary. The operation of this switching system is described below.

TRANSMITTER SELECTOR SWITCH

The transmitter selector switch (figure 6-1) 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
6-2