TM 11-6625-821-45
ability to remove this ground which, in turn,
reduces the gain of the servoamplifier that
.
drives the servoamplifier that drives the servo-
A regulated +15 volts dc from voltage reg-
driven goniometer. With ground removed, a
ulator Q30 and Q31 in the receiver is con-
constant error can be applied to the servo-
nected through rear switch wafer S4C in the
amplifier with the receiver in ADF mode.
test set to the control unit. When function
When LOOP switch S303 is rotated to R
switch S302 in the control unit is set to either
(right), phase 1 of the 110-cps signal is con-
ANT or LOOP position, the + 15 volts dc is
nected to the manual loop control circuit in
attenuated by variable resistor R301C. This
the receiver. This signal drives the servo-
voltage is applied through front switch wafer
driven goniometer clockwise. When LOOP
S4C in the test set to the receiver where the
switch S303 is rotated to L (left), phase 2 of
voltage is used to bias transistors Q2, Q4, Q7,
the 110-cps signal is connected to the manual
and Q8. In the LOOP position of function
loop control circuit in the receiver. The phase
switch S302, resistor R303 is added to the at-
2 signal is 180 out of phase with the phase
tenuating circuit and decreases the receiver rf
1 signal and, therefore, drives the servo-driven,
gain to compensate for the increase in gain
goniometer counterclockwise.
When LOOP
caused by switching out certain signal attenuat-
switch S303 is in the first position, left or
ing networks in the receiver rf stages during
right, the magnitude of the two 110-cps sig-
loop operation. Thus, receiver rf gain is prac-
nals is attenuated by resistors R306 and R307.
tically the same in either antenna or loop op-
These two switch positions are slow-speed po-
erating modes for the same rf GAIN control
sitions, providing a slower speed of gonio-
setting. In ADF mode, variable resistor R301C
meter rotation than the second switch position,
is bypassed through rear switch wafer S302A,
left or right.
applying + 15-volt dc bias without attenuation.
Note that turning the GAIN control clockwise
rotates R301 counterclockwise.
Circuit
Circuits
The audio output from the receiver is con-
nected through front and rear switch wafers
a. Bfo Switching Circuit. The control unit
S4B in the test set to control unit function
BFO-OFF switch controls operation of bfo Q21
switch S302, which is shown in the ADF posi-
in the receiver by supplying or removing emit-
tion. Variable resistors R301A and R301B, in
ter and base-bias voltages. A regulated source
conjunction with resistors R304 and R305,
form a bridged-T attenuator, which presents a
of + 15 volts dc from the receiver is connected
through rear switch wafer S4C in the test set to
constant 600-ohm output impedance to the test
set, When function switch S302 is set to either
one side of BFO-OFF switch S301 in the con-
trol unit. Setting switch S301 to BFO connects
ANT or LOOP position, the variable resistors
the +15 volts dc through front switch wafer
are shorted out by contacts 4 on the front and
rear wafers of S302A. Note that turning the
S4A in the test set to Q21 in the receiver, caus-
GAIN control clockwise rotates R301 counter-
ing the bfo to oscillate, When the BFO-OFF
clockwise. The audio signal from the control
switch is in the OFF position, the + 15 volts dc
unit is applied to AUDIO OUT terminals J1
is removed from Q21 and bfo cannot oscillate.
and J2 on the test set through rear switch
b. Tuning Meter Circuit. The intermediate
wafers S4B and S4C. When a headphone plug
frequency (if. ) signal in the receiver is recti-
is connected to PHONE jack J5, the PHONE
fied and applied to tuning meter M301 in the
jack connects itself to the audio output sig-
control unit through rear switch wafer S4A in
nal and disconnects the AUDIO OUT termi-
the test set. The rectified if. signal is propor-
nals from the signal. This eliminates the possi-
tional to the if. amplifier signal and reaches
bility of double loading the audio output cir-
maximum amplitude when the receiver is tuned
cuit of the receiver.
to the rf carrier of a radio station.
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