Cessna 172S Pilot Operating Handbook page 190

SECTION 9 - SUPPLEMENTS
SU PPLEM ENT 20 - FAA APPROVED
In this stereo installation, all headset locations are wired in
parallel. If a monaural headset is plugged in at any
location, one intercom channel will be shorted. Although no
damage to the intercom will result, all stereo headset users
wil l lose one audio channel.
perform normally.
A crystal-controlled superheterodyne marker beacon receiver
with 3-light presentation is incorporated within the unit.
circuitry for the marker beacon lamps automatically adjusts
brightness appropriate to the cockpit ambient light level. HI and LO
sensitivity and lamp test/receiver audio m ute (T/M) functions are
also provided.
Light dimming for the audio control panel is manually controlled
by the RADIO light rheostat knob.
MARKER
Inner,
Continuous 6 dots/sec (3000 Hz)
&
AilWay
Fan
M iddle
Alternate dots and dashes ( 1 300 Hz)
Outer 2 dashes/sec (400 Hz)
"'When the identifying tone is keyed, the
respective indicating light will blink
accordingly.
S20-4
N OTE
The monaural headset will
M A R K E R FACI LITI ES
I D E NTIFYI N G TONE
C ESSNA
MODEL 1 72S
Dimming
L1G HT*
White
Amber
Blue
Dec 30/00