(3) Tuning Knobs. Two concentric tuning
knobs, located on the right side of the NAV/TACAN
control panel, are used to set the frequency or TACAN
channel shown on the digital display, depending on the
mode being used.
Standby Entry Mode. When the unit is in the
frequency or TACAN channel standby entry mode, the
larger concentric knob is used to increase or decrease
the first two digits to the left of the decimal point from
08 to 17 MHz (frequencies) or 01 to 29 (TACAN
channels) of the standby digital display. When the
larger concentric knob is turned to increase the digits
above 17 (frequencies) or 29 (TACAN channels), the
display will start over at 08 or 00 respectively.
Conversely, when the knob is turned to decrease the
digits below 08 (frequencies) or 00 (TACAN channels)
the display will start over at 17 or 29 respectively.
When in the frequency mode, the smaller concentric
knob, placarded PULL Y, is used to set frequencies
with 50 kHz spacing (i.e., .75, .80, .85, .90, etc.).
When in the TACAN mode with the smaller concentric
knob turned in the pulled-out position, the TACAN X
designator will be changed to Y.
When in the active entry mode, the tuning knobs
operate the same as they do in the standby entry
mode, but will change the upper digital display
frequency or TACAN channel rather than the standby
(4) MODE Switch. A momentary push-
button switch, placarded MODE, located on the lower
portion of the NAV/TAC control unit, is used to put the
unit into the TACAN mode. Momentarily pressing the
MODE switch while in a frequency mode puts the unit
into the TACAN mode.
(5) OFF /VOL / PUSH TST Control. A
control knob on the front of the NAV/TACAN control
unit, placarded OFF / VOL / PUSH TST, controls the
operation of the unit. Turning the knob in the
clockwise direction from the OFF position (detent)
applies power to the unit and audio volume output is
increased as the knob is turned further to the right.
Pressing PUSH TST overrides the automatic squelch
circuitry. Turning the knob clockwise past the
automatic squelch threshold, while the automatic
squelch circuitry is overridden, will allow background
audio to be heard through the headphones or speaker
and demonstrate whether the receiver is working or
not, and allow setting of audio volume. To return the
unit to automatic squelch control, press the PUSH TST
control knob again.
c. Modes of Operation. The NAV/TACAN
control unit may be operated in TACAN or frequency
mode in either standby entry or active entry mode.
(1) Standby Entry Mode (Frequency or
TACAN Channel). When the unit is operated in the
standby entry mode, a new frequency or TACAN
channel is set on the standby digital display, using the
tuning knobs. When the operator is ready, the
frequency or channel is transferred to the active
display by pressing the transfer switch.
Channel). When the unit is operated in the active
entry mode, a new frequency or TACAN channel is set
on the active digital display using the tuning knobs.
The active entry mode is entered from the standby
entry mode by pressing the transfer switch for longer
than 2 seconds. The standby digital display will be
blank while the unit is in the active mode.
(3) TACAN Mode. Enter the TACAN mode
by momentarily pressing the MODE switch. While in
this mode, the tuning knobs change the TACAN
(1) Turn On Procedure.
1. Avionics Master Switch (overhead
control panel, Figure 2-15) ON.
2. OFF / VOL / PUSH TST Knob Turn
clockwise out of detent, then press to
turn off automatic squelch circuit.
Continue turning knob clockwise until
headphones or speaker, assuring that
receiver is operating, then set audio
volume to desired level. Press knob
again to return unit to automatic
(2) Receiver Operating Procedure.
1. MODE Push-Button Switch As
2. Tuning Knobs Set desired frequency
3. NAV I Receiver Audio Switch (audio
control panel, Figure 3C-1) ON (up).
4. VOL Control Adjust as required.