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“COMM 1 and COMM 2 control heads”, are installed on the cockpit center
pedestal. The COMM 1 and COMM 2 control heads form the
communications portion of what is commonly known as the “six pack”
configuration. Four other Gables digital frequency control units, two for
navigation control (NAV 1 and NAV 2) and two for automatic direction
finding control (ADF 1 and ADF 2), complete the six pack concept.
C. VHF Antennas:
The two VHF antennas (No. 1 and No. 2) are blade-type antennas that
operate throughout the frequency range. The VHF No. 1 antenna is located
on the bottom of the fuselage along the centerline. It provides full
hemispherical coverage. The VHF No. 2 antenna is located on the upper
portion of the fuselage. It provides coverage for communication on the
ground.
3. Controls and Indications:
(See Figure 2.)
A. Display Window:
Each control head has a two-section display window. The upper section
display consists of a five digit display indication referred to as the active
display. The lower section display consists of a five digit display indication
of the preselected frequency that is available for interchange with active
display. It is referred to as the preselect display.
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-23-00
Page 5
May 30/02
Revision 7
B. Power ON Switch / Volume Control:
A rotary switch is located within the frequency selector knobs that is used
to apply power to the control head and control volume.
C. Frequency Selection Knobs:
Dual concentric control knobs provide control of the preselect display and
frequency / code information encoded into data sent to the radio
equipment. A feature of the knob is variable rate tuning, which makes the
tuning process much faster. When a single control knob has a wide range
to control, the more rapidly the knob is rotated, the more range per detent
is covered. Clockwise rotation increases the frequency while
counterclockwise rotation decreases the frequency.
The tunable range is from 118.00(0) to 151.97(5) MHz (inclusive) in 25 kHz
steps. The 0.001 MHz digit is not displayed.
The 0.1 and 0.01 MHz digits are controlled by the smaller frequency
selector knob. Each detent of the knob will vary the display in 0.02(5) MHz
increments. The digits range from 0.00(0) to 0.97(5).
The 100 MHz digit is a constant 1. The 10 and 1 MHz digits are controlled
by the larger knob with each detent altering the display by 1 MHz. The
digits range from 118 through 151 MHz.
D. Active / Preselect Frequency Interchange Switch:
A push button switch located on the left of the display window provides a
means of exchanging active and preselected frequencies.
E. MEMORY 1 / 2 Switches:
Push button MEMORY switches provide additional preselected frequency
storage. Activation of these switches will illuminate / extinguish the
MEMORY 1 / 2 indicators. When depressed from an extinguished state, the
previously stored frequency will be transferred to the preselect display. This
frequency is now available for ready interchange with the active display.
Depressing the switch from an illuminated state causes storing of the
current preselect frequency and extinguishing of the indicator. The
indicators (white) are located in the push button switches and indicate
which memory location is active and displayed on the lower display.
With one MEMORY switch active (illuminated), depressing the other
MEMORY switch or the frequency interchange switch will extinguish the
currently illuminated indicator and store the displayed frequency. This
frequency is stored in the memory location that corresponds to the
indicator just extinguished.
F. 121.5 Switch:
A two position recessed toggle switch provides direct access to the VHF
guard frequency of 121.50 MHz when placed in the 121.50 position.
Provided a COMM control head failure has not occurred, the active display
will indicate a frequency of 121.50 MHz. This access discrete is also used
by the VHF transceiver to cause direct radio channeling of 121.50 in the
event of a COMM control head failure.
When the 121.5 switch is placed back in the TUNE position, the COMM
control head will again transmit the previous active frequency displayed in
the upper display before 121.5 was selected.
OPERATING MANUAL
2A-23-00 PRODUCTION AIRCRAFT SYSTEMS
Page 6
May 30/02
Revision 7
For aircraft with 8.33 kHz channel spacing capability, the TUNE /
121.50 switch is relabeled and reprogrammed to enable either 25 kHz
spacing or 8.33 kHz spacing tuning capability. To switch between either
kHz spacing, the flight crew should:
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湾流4操作手册 Gulfstream IV Operating Manual 1(49)
