To return to the preset frequency selection mode,
push the ACT switch again for 2 seconds. As a safety
feature, the ADF receiver control unit automatically
switches to the active frequency selection mode when a
frequency select knob is operated while the STO, TEST,
or XFR/MEM switches are actuated, or the memory recall
inputs to the control are grounded.
(4) Frequency storage. Up to four preset
frequencies can be stored in the memory in the ADF
receiver control unit for future recall. To program the
memory, select the frequency in the preset frequency
display using the frequency select knobs and push the
STO switch once. One of the channel numbers (CH 1
through CH 4) will appear in the active display for
approximately five seconds. During this time the channel
number can be changed without changing the preset
frequency by momentarily positioning the XFR/MEM
switch to the MEM position. After the desired channel
number has been selected, push the STO switch again to
store the frequency.
When storing a frequency, the second actuation
of the STO switch must be done within 5
seconds after selecting the channel number or
the first actuation of the STO switch. If more
than 5 seconds elapse, the control will revert to
the normal modes of operation and the second
store command will be interpreted as the first
After a frequency has been stored in memory, it will
remain there until changed by using the STO switch
Memory is retained even when the unit is turned off for an
extended period of time.
Power and mode switch - ANT, ADF, or
Tuning knobs - Set desired frequency.
ANT function - Position power and mode
switch to ANT. Select ADF on audio
system and adjust volume.
ADF function - Position power and mode
switch to ADF. Bearing pointer will
indicate relative bearing to tuned station.
When the ADF system is not receiving a reliable
signal, bearing pointer will be removed from
momentarily blank during station crossings
because of signal loss.
TONE function - Position power and
mode switch to TONE (BFO). A 1000-Hz
tone will identify keyed CW stations.
Power and mode switch - ADF.
Tuning knobs - Tune a nearby NDB,
compass locator, or broadcast station.
TEST switch - Depress. Bearing pointer
will rotate 90 degrees from the previous
valid indication. Release TEST switch
and verify that the bearing pointer returns
to previous valid indication.
If the signal received is weak or of poor quality,
bearing pointer rotation will be slow.
ADF receiver fault codes are listed in table 3-8.
TACAN/DME SYSTEM (AN/ARN-154).
a. Description. The TACAN/DME system (fig. 3-26)
operates in conjunction with TACAN and VORTAC ground
stations to provide distance, groundspeed, time to station,
and bearing to station. The TACAN/DME system
electronically converts elapsed time to distance by
measuring the length of time between the transmission of
a radio signal to a selected DME/TACAN station and the
reception of the reply signal. The distance is measured
on a slant from the aircraft to the ground station and is
commonly referred to as slant-range distance. Slant
range approximates actual ground distance. The
difference between slant-range distance and ground
distance is smallest at low altitude and long range, and
greatest when in close proximity to the selected ground
station. The system is capable of tracking the range of up
to four stations and the bearing of two stations
simultaneously. The system will operate on any one of
252 preselected frequencies (126 X mode and 126 Y
mode channels). Course deviation, bearing to station,
and distance to TACAN or VORTAC stations are
displayed on the EHSI. Distance, time to station, bearing,
station identifier, and groundspeed may be displayed on
the TACAN digital display. The TACAN/DME also
provides distance information to the inertial navigation
system (INS). The system is protected by a 2-ampere
circuit breaker placarded TACAN, located on the
overhead circuit breaker panel (fig. 2-7).
TACAN Control Unit Controls and Functions (fig.
(1) TACAN channel display. Indicates selected