TM 11-5826-225-35
excitation and MC1, is derived from a dc-to-ac
transformer T18 and the collector of second
resolver servoamplifier Q18. Terminal 2 of
voltage inverter located in the receiver mount.
All electrical connections between the control
T18 is then used as the servoamplifier input
Phase 1 of the 110-cps signal applied to push-
unit and receiver are made through the re-
pull resolver servoamplifier Q24 and Q25
ceiver mount and airframe cabling.
causes clockwise rotation (to right) of resolver
B3 functioning as a goniometer, and phase 2
1-29. Manual Loop Control
of the 110-CPS signal causes a counterclockwise
rotation (to left). Synchro transmitter B4 and
a. The direction finder set uses a servo-driven
the aircraft bearing indicator follows resolver
resolver functioning as a goniometer instead of
B3.
the conventional rotating loop antenna used
c. When manual goniometer rotation is de-
in some adf systems. A goniometer generates a
sired while operating in adf mode, the control
r o t a t i n g figure-eight loop antenna pattern
unit function switch is set to ADF position.
identical to that produced by a rotating loop
Switch S1L, operating through the control
antenna. The aircraft bearing indicator follows
unit and receiver autopositioner circuit (para
the goniometer rotor position and indicates the
127), removes the ground from the collector
azimuth or direction in which a loop antenna
of Q18 (fig. 514). Normally in adf operation,
would point to if it could rotate. A loop switch
the collector voltage and current path of Q18
on the control unit enables the operator to posi-
is through grounded LOOP switch S303 and
tion the goniometer and bearing indicator
the primary winding of T18. Positioning LOOP
manually for either manual direction finding or
switch S303 either right or left opens the col-
to check the precision of bearing indication in
lector circuit and thus disables adf operation.
adf operating mode. This is accomplished by
The resistance of R133 is sufficient to prevent
observing the precision in which the bearing
Q18 from receiving collector voltage while pro-
indicator pointer returns to its original bearing
viding a ground return for T18. These circum-
indication after the goniometer rotates past a
stances permit manual goniometer rotation in
null position. When manual direction finding
adf operating mode. All electrical connections
mode is desired, the operator sets the control
between the control unit and receiver are made
unit function switch to LOOP position.
t h r o u g h the receiver mount and airframe
b. In figure 514, two phases of 110-CPS sig-
cabling. For resolver servo amplifier circuit
nals derived from the receiver 110-CPS oscilla-
details refer to paragraph 118.
tor Q22 are applied to LOOP switch S303.
Switch S303 has two positions right or left,
130. Manual Audio and RF Gain Control
with spring return to its center or grounded
When the direction finder set is operated as
position, In the first position left or right, the
an automatic direction finder (adf), audio gain
magnitude of the 110-CPS signals are attenuated
is controlled by dual gain potentiometers in the
by resistors R306 and R307. These two switch
control unit. The RF gain cannot be varied
positions are slow speed positions, providing a
manually. In antenna and manual direction
slower speed of goniometer rotation than the
finding modes, RF gain is controlled by a po-
second switch position left or right. When
tentiometer ganged to the audio gain poten-
switch S303 is in its center position, the servo-
tiometers. Audio gain cannot be varied.
arnplifier manual loop control signal path is
a. Manual Audio Gain Circuit (fig. 5-15).
grounded, preventing spurious signals from
affecting adf operation. Positioning switch
The receiver audio output from transformer
S303 either right or left applies either phase
T20 is applied through connections in the re-
1 or phase 2 (180 out-of-phase with phase 1 )
ceiver mount and airframe cabling to control
to servoamplifier input transformer T18, When
unit function switch S302, which is shown in
the control unit function switch is set to LOOP
ADF position. Variable resistors R301A and
position, switch S1-L grounds terminal 1 of
R301B, in conjunction with resistors R304
Change 1 1-27
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