Garmin GNC 420 - Manual (Page 29)

GNC 420(A) Pilot’s Guide and Reference 2-1
SECTION 2
COM
190-00140-20 Rev. K
SECTION 2: COM
2.1 COMMUNICATING USING THE GNC 420
The GNC 420 features a digitally-tuned VHF COM radio
that provides a seamless transition from communication
to navigation, bringing the two most important functions
in flying together in one panel-mounted unit. The GNC
420’s COM radio operates in the aviation voice band, from
118.000 to 136.975 MHz, in 25 kHz steps (default). For
European operations, a COM radio configuration to allow
for 8.33 kHz steps is also provided (Section 9.5, Setup 2
Page: COM Configuration).
Volume
COM radio volume is adjusted using the COM Power/
Volume Knob. Turn the COM Power/Volume Knob
clockwise to increase volume, or counterclockwise to
decrease volume.
Squelch
The COM radio features an automatic squelch,
providing maximum sensitivity to weaker signals while
rejecting many localized noise sources. The pilot may
wish to override this automatic squelch function when
listening to a distant station or when setting the desired
volume level. The COM Power/Volume Knob allows the
pilot to disable the automatic squelch and keep the COM
audio open continuously.
Overriding the automatic squelch:
1) Press the COM Power/Volume Knob
momentarily.
2) Press the COM Power/Volume Knob again
to return to automatic squelch operation.
COM Window and Tuning
Communication frequencies are selected with the
tuning cursor in the standby COM frequency field (Figure
2-1), using the small and large left knobs to tune the
desired frequency. The standby frequency always appears
below the active frequency. The active frequency is
the frequency currently in use for transmit and receive
operations.
Figure 2-1 ‘RX’ Receive Indication
‘RX’ Receive Indication
Standby COM Frequency Field
A frequency may also be quickly selected from the
database by simply highlighting the desired frequency on
any of the main pages and pressing the ENT Key. This
process is referred to as auto-tuning. Once a frequency is
selected in the standby field, it may be transferred to the
active frequency by pressing the COM Flip-flop Key.