BENDIX ADF-T12B Maintenance Manual page 14

D E S C R I P T I O N A N D O P E R A T I O N
The optional speaker amplifier is connected to the output of push-pull audio amplifier Q12 and Q13.
The output of the push-pull amplifier circuit in the optional speaker amplifier is reproduced in the
s p e a k e r .
C C .
The output of the 1st audio amplifier in the servo amplifier-indicator is applied to three additional
stages of audio amplification where the signal is brought to the necessary amplitude required to drive
t h e s e r v o m o t o r .
D D .
The output of the 4th audio amplifier is also applied to the input of the filter. The filter is designed
and adjusted to reject the 47 cps component while feeding back the higher frequency audio components.
Consequently, the original 47 cps signal applied to the input of the balanced modulator from the output
of the power oscillator is recovered at the output of the 4th audio amplifier in the servo amplifier-
indicator and applied to the control windings of the servo motor through motor control amplifier stage
Q5 and Q6.
E E .
The low-frequency power oscillator produces anominal 47 cps signal. This signal, besides being
applied to the balanced modulator stage in the ADF receiver, is also applied to the motor control
amplifier as areference voltage. The recovered 47 cps at the 4th audio amplifier output is compared
in phase and amplitude with the 47 cps reference voltage. The resultant signal serves to drive the
servo motor in the proper direction.
F F .
8 . P H A S E R E L A T I O N S H I P S
A. The phase relationships that exist between the loop r-f, sense r-f and the low frequency (47 cps) modu¬
lating signals during ADF mode of operation are indicated in Figure 4.
B. Normally, the modulated voltage waveforms shown in the illustration, if observed on a"scope", would
appear as square waves. The sine waves depicted are shown for clarity and ease of understanding.
TTie numbers in parentheses listed below correspond to the numbers to the left of each waveform in
the illustration. The explanation follows the corresponding number for each of the waveforms illustrated.
(1)
The output of the sense antenna is of constant phase.
The output of the resolver rotor coil (loop antenna input signal) is 90-degrees out-of-phase with
the sense antenna r-f input signal and either leads or lags the sense r-f (by 90 degrees) depending
on whether the resolver rotor coil is to the right or left of the "true" null position.
(2)
(3) The resolver rotor signal is shifted in phase an additional 90 degrees. This results in the output
of the loop r-f amplifier being in phase or 180 degrees out-of-phase with the incoming sense antenna
s i g n a l .
The resolver rotor coil output signal is applied to the input of the balanced modulator. (4)
The low-frequency output (47 cps) of the power oscillator is also applied to the input of the balanced
modulator. The modulation voltage (47 cps) causes the four diodes of the balanced modulator
circuit to be switched (as pairs) on and off in phase opposition during each half-cycle of the modu¬
lating voltage.
(5) and (6)
The balanced modulator produces a47 cps modulated loop r-f output signal in which the phase of the
r-f component undergoes a180 degree phase reversal during each half-cycle of the modulating signal
(47 cps). The phase of the loop r-f output of each pair of diodes in the balanced modulator with
respect to the resolver rotor input voltage is afunction of the position of the rotor coil with respect
to the "true" null position.
The sense antenna signal (1) is illustrated again, below the output of the balanced modulator (7 and
8 ) f o r c l a r i fi c a t i o n .
(7) and (8)
(9)
When the resolver rotor coil is to the left of "true" null, the sense and loop r-f signals combine
in the sense antenna transformer and reinforce the output of one pair of diodes in the balanced
modulator circuit and reduces that of the other pair. When the rotor coil is to the right of "true"
null, the same effect occurs but in opposite sequence.
(10)
A P R I L 1 9 6 5
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