DESCRIPTION AND OPERATION
Durinf,' the next half-cycle of the incoming switching voltage, diodes CR2 and CR3 are "shut-off" or
non-conducting while diodes CRI and CR4 are conducting in the direction shown in figure 7. The
polarities of the fr'ur diodes therefore reverse themselves from that of the first-half cycle of switching
voitage. In this case, the conducting path through the circuit is now 180 degrees out-of-phase with the
conducting path of the first half-cycle as can be seen by comparing the simplified equivalent circuits
below each figure in the illustration.
G.
11. DETAILED CIRCUIT DESCRIPTION: MOTOR CONTROL AMPLIFIER
A.
The motor control amplifier stage consists essentially of transistors Q5 and Q6, the secondary wind¬
ing of transformer T-1, alow-pass filter network and the d-c servo motor.
The purpose of the motor control amplifier is to amplify and compare the relative phase and amplitudes
of both the 47 cps power oscillator reference voltage and the incoming 47 cps variable ADF voltage.
This is necessary in order to arrive at aresultant voltage that will control the direction of rotation of
the servo motor. Consequently, this will enable the r-f resolver rotor coll to stop rotating upon
reaching the "true" null position.
B.
C.
The output of the 47 cps power oscillator is applied to the Input of the motor control amplifier through
the secondary winding of transformer T-1 (See Figure 403). As aresult, asquare-wave voltage exists
at the bases of transistors Q5 and Q6 that are 180 degrees out-of-phase due to the center-tapped
secondary winding of transformer Tl. The two signals are of equal amplitude.
The recovered ADF signal is coupled through capacitor C8 to the center tap secondary of Tl and applied
in-phase to the bases of transistors Q5 and Q6. Therefore, upon receipt of aloop r-f signal, two
signals, algebraically added will exist at the bases of transistors Q5 and Q6. One signal being the
recovered 47 cps variable ADF signal from the output of the ADF receiver and the other signal being
the 47 cps reference output signal from the power oscillator. The ADF variable signal is the same phase
at both transistor bases. The power oscillator reference signal is 180 degrees out-of-phase at both
t r a n s i s t o r b a s e s .
D.
E.
Figure 8Illustrates the operation of the circuit when the relative bearing of the aircraft from the
station is 45 degrees (right). Figure 9illustrates the operation of the circuit when the relative bearing
of aircraft from the station is 225 degrees (left). Figure 10 Illustrates the operation of the circuit when
the relative bearing of the aircraft from the station is zero degrees; that is, the aircraft pointing
directly to the transmitting station.
F.
Referring to Figure 8it is Indicated by the position of the aircraft in relation to the transmitting station
that the ADF indicator pointer should rotate in aclockwise manner and stop at the 45 degree mark on
the calibrated dial.
G.
It will be assumed that the output at the collector of transistor Q5 causes clockwise rotation of the servo
motor armature while the output at the collector of transistor Q6 causes counterclockwise rotation of
t h e m o t o r a r m a t u r e .
H.
It will further be assumed, for the sake of clarity, that the amplitude of the 47 cps oscillator output
signal Is 5vac and the amplitude of the ADF signal at the bases of Q5 and Q6 Is 10 vac. The Incoming
ADF signal will either add to the 47 cps oscillator signal at the base of Q5 and subtract from the 47
cps oscillator signal at the base of Q6 or vice versa.
I.
Due to the action of the mixed loop r-f and sense r-f signals at the output of the balanced modulator
isolation amplifier, the ADF signal (in this case) adds (or aids) the oscillator signal at the base of Q5
and subtracts (or opposes) the oscillator signal at the base of Q6. This is indicated in (a) and (c) of
Figure 8. The resultant signal derived from the algebraic summation of the two signals is indicated
in (b) and (d) of the figure.
J.
Consequently, during the fir.st half-cycle of the resultant signals ((b) and (d)), the bases of transistors
Q5 and Q6 are positive enough with respect to their emitters to cause astate of reverse-bias in both
transistors. I n other words, n e i t h e r transistor is c o n d u c t i n g during this first half-cycle of resultant
voltage. As aresult, there is no output at the collectors of both transistors. Hence, the servo motor
a r m a t u r e d o e s n o t r o t a t e .
Page 17
(Revised October 1969)
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General